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"Landforms and Weathering on McKeen Ridge, -*CatfiedralPark, B C. " ' ~ITLEOF THESISITITRE DE LA TH~SEJ .
DEGREE FOR WHICH THESIS WAS FESENTEDI Master of ARts , GRADE POUR LEOUEL CETTE THESE FUT PR~SENT~E rl YEAR THIS DEGREE CONFERRED!ANN~DrOBTENTlaY DE CE DEG~ tQ76 Professor F.F. Cunningham NAME OF SUPERVISOR/NOM DU DIRECTEUR DE TH.!?SE -- -r--
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Canadian Thes Division Division des theses canadiennes Cataloguing Br7 nch Di rection* du catal ogage National Librar"y of Canad? Bi bliotheque nationale du Canada Ottawa, Canada KIA ON4 Ottawa, Canada . KIA ON4
Y- BAKons,, University ef California, Berkeley, NU
. %. A THESIS SUBMITTED LN PARTIAL FULFIL- OF
THE REQUIREMENTS FOR THE DEGREE OF 7 MASTER OF ARTS
in the Department
Geography
@ PAUL ZENOPE MELOOW 1975
SIMON WSER UNIVERSITY
All rights reserved. This thesis my not be .reproduced in whole or in part, by photocopy - 7 or other means, without permission of the author. APPROVAL
Name : Pau 1 Zenope Melcon
Degree : Master of Arts
Title. of ~hesis: Tors and Weathering on ~cKeenRidge, Cathedral
Provincial Park, British cbldia
-- -
Examining CommitQe: ~ , -, P,
Chairman: R.B. Horsf all.
- --r,. - - - ,- V F.F. (Cunningham Senior 'Supervisor
I
. - . C. B, Crampton
-, F - -.-, -- L.K. Peterson External Examiner Associate Professor Chbistry Departmen? - Simon Fraser Universiq -.
Date - Approved : .+ .+ .% ' . PARTIAL COPYRIGHT LICENSE , --- - -
4
4 I hereby grant to Simon Fraser University the right to lend
.I my thesis or dissertation (the title of which is showd beiow) to users
of the Simon Fraser University Library, BW to make dartial or single
copies only for 'such users or in response to a requcst from the library
- of any other university, or other educational institution, on its'own I I , -& A ---- - beha16 or for one of its users. I further agree that permission for
multiple copying of this thesis for scholarly purposes may be granted
by me or the Dean of Graduate Studies. It is understood that copying
or publication of this 'thesis for financial gain &hall not be allowed .- without my written permission.
Title af Thesis/~issertation:
, Author : , ,-_--, ,-- , , ,, ?
,- PAUL Z. MEXON --
7 (name ) . . - # August 20, 1975 .
(date)
= 4: Abstract
This the;is, titled Tors and Weathering on ?&een Ridge, Catheiral , Provincial Park, British ~olumbi~,is an analysis of the morphogenesis of'a * tor landscaie located on an alpine ridge in the interior of British Columbia
-- 4 in the light of a critical review of the scientific literaturewconcerned with tors and related topics. Tors are a bedrock landform having an unusual and
- - -- - distinctive appeara ce which have been investigated by geomo~pbologistssince - 7- the middle part of the nineteenth century. Despite the considerable scrutiny
.-a to which tors have been subjeebd, major questions regarding the origin and f. development of these landforms remain to be resolved, Specific problems inclu'de the age of particular tors, the climate and geomorphic conditions " under which they evolved, the effect of Pleistocene ice sheets and peri- glacial conditions on tors in middle and polar latitudes, and the changes 9 , occurring in tors exposedcto subaerial weathering conditions, Although many tors are regarded as havgng been produced by chemical deco&mition inva subsurface environment, this single explanation cannot be extended to all
.tors. Tors have been attributed to either slope retreat or fmst action, and they have also been regarded as structural landforms or relict features.
I I
I The tors on McKeen Ridge were examined during field work in the summer and fall of 1974, and the surnmer of 1975. The field work consisted of geo-
logic mapping, the collectionnf rock and fossil specimens, examination $2 . ..;- - of the landforms and geomorphblogy of the ridge, a seis&c,survey, and a
thorough study of fie tors themselves. It was augmented by. laboratory
examination of the rock specimans and residual materials, Experiments * testing ae- reaction of certain samples to simulated weathering conditions
were conducted. A conc~usionof thisP€Fesfs is thXtFt6rs piissessing morphological characteristics .de,scribed-inthe text are azonal landforms having their origin by chemical weathering in a subsurface environinent and-are exposed at the sur,face by removal of @e unconsolidated products of weathering by -*. - erosional process&. ~lthou~~~chernicalweathering, deep regolsths and tor
formation are often regarded as tropical phenomena, it is proposed that-deep
that the rate of chemical decomposition of rock material is.greater than the . . rate of removal of the products of' decompositign by erosional processes, '- Tors -cannot, therefore, be regarded as indicators of paleoclimatic conditions. The capacity of tors to survive periglacial conditions and subrergence
beneath continental ice sheets has also been discussed. It is proposed that . . deep weathering landscapes may 'have been present over wide areas in northern
latitudes during the Tertiary. >
Evidence obtained from field and laboratwy74 investigatians of,the tors - ..*e' on McKeen Ridge supports many conclusions reached in the literature review,
The tors-are shown to be paleo-landforms having their origin in a subsurface
environment by chemical weathering of quartz monzo&$te bedrock, The tors , were exhumed and then buried beneath lava flows an3 a fossiliferous sediment
during the Eocene. Indirect evidence suggests that the tors my be as old - as' the beginning of the Tertiary, Paleoclimatic evidence from local 'fossils . in the Eacene sediment indicate the presence of a w , ,mist and equable "6" -- - - climate which was neither tropical nor subtropical, A low relief "peneplainH t - . 3 - g* - surface was present in this British Columbia during the Early .A C * 5 ? Tertiary. The combination of low relief (and therefore slow rates of denu- a r dation) agd an equable, mist climate fulfills the conditions necessary I
------7 for deep weathering to occur. Factors establishing the subsurface origin
-of the tors include the morphologfc characteristics of the tots themselves, B * the degree o-f chemical alteration of the-quartz monzonite bedrock in which , the ,tors"are formed, and the pr5sence of weathered materials derived fiom .
the quartz monzonite in the Eocene sediment. The tors were re-exhumed during s - * the Pliocene or Pleistocene and have sutvived submergence beneath Pleistocene , - + ice sheets. A new mechanism responsible for the origin of weathering pits s., s., -
on tors is described. :-..., 2 - . The major contribution of the field work is the documentation of the r -6 age, climatic conditions and geomorphic environment under which these tors evolved. The tors constitute the oldest tor landscape tb e brigin of which 1 has been conclusively established, and the first tor landscape in which , direct evidence was 'present indicating that the tors evolved under-bid-
latitude climatic conditions. - K 'I wish to thank Professor F.F. Cunningham, my thests supezvisor, r t - gr. C. B . Crampton, and Dr-. L. *K. Peterson *for their valuable criticism an& assistance in the preparation of this thesis.
I wish< to acknoklede'Z. P. Melcon, M. C.cMelcon, D. J'. Uelcon,
.B. A. Popelak,.E. M. Leonard, and W. A. Wetzel for their assistance in the
field, I am particulakly 'indebted to &of essor-~unnin~&amfor k~-xf&alAs- -
comments in the field, and-his enthusiasm and'interest in this thesis.
, ,. . I wish to thank my wife, &errill, for her unwavering assistance and
'loving support in the preparat ion of this thesis.
art TABLE OF CONTENTS
LIST OF FIGURES ...... :...... -...... ,...... ,..,...... ,.. x
- - - A -- - LIST OF PR(5FGRMI-G ...... -.....,.-- -&.-. xi .<
r?
Introduction ...... ,...... ,,.,...... ,.....-..-* r 1 Tr Physiography ...... ,...... -.... 3 Location ...... 3 Access ...... ,..,,...... ;...... -...... 5 *, Climqe ...... :...... ,...... r.,,...... 7 soil k...... 9 vegetaGion ...... ,...... ; ...... 11 ~ekog~...... ,,..,.,.; ...... '13 . Bradshaw, Iqdependence, Shoemaker and Old Tom Formations ...... 15 Nicola Group ...... 19 Jurassic and Cretaceous ...... 22 Tertiary ...... 28 fl.~' Pleistocen'e 36 ..,,,...,...,,...... ,...... ~...... , 15 andf forms ...... 41 Tors ...... /...... '...... ,...... -.... 43 Literature Review .;...... -...... 55 Introduction I; ...... 55r Tor and Inselberg ~heories...... 57 Two Sta9 e or Multicyclic Morphogentsis ...... 58 heStage Morphogenesi? ...... ,...... ,,...... -...... 63 Fluvial Erosion .,~.,&~...... ,.....,..s...... 65 , =, Structural ~heoiiks 67 - :...... ,...,...... ,....- - Chemical Weathering ...... : .. ..ie-...... 69 Spheroidal Feathering .;.,...... ,...... -..< I 74 Non-meteor* Alteration ...... :,...... ,..-...... < 78 - Petrology ...... -.....,....~...,,...... 82 Deep Weathering ...... ;..-..., 90 Climate ...... ~.....,...... 92 Jointing ...<...6...... 8...... 103 Subaerial ~mlution...... 112 C Table-cd Gknttents Page .. Glaciation ...... ;...... L...~...... --.....- 120 Dating -...... -.....-...'>.....,.:....---.---- I 127 Analysis of Cathedral Park Tors ...... :...-....- ~orp'h~~enesis...... : ...... ,.:. i.: ...... Current Weathering ...... -:...... Micro-forms ...... I A. Concluding Remarks ...... 9...... ;....-... , Bibliography ...... e...,...... ,,...... viii ' t - 1 0 - -, ~~ ---- -~ -- - 2. - - -.. . I 2:: J 9' 9' -. ' 4 ------~ - - - f LIST OF TABLES ,' i ! -,..$ d Table I Page *. - I.-Selected Climatic' Data ...... "-8 ,-s . 11. -Chemfical. Analysis of the Cathedral - quartz monzonite ...... ,....t...... ,.....,...... 2 4 111,-Recent ashfalls in the NW U.S.A. and SW Canada .....,..,.,...,...,.,...... 2...... -...... *...,35 J & - 1V.-&wen's reaction series ...... z...... ;...... ,...... -- 83 V.-Relative dissociation of water with temperature ...... 9 3 ,' " > . 5. *i: -- < **LIST OF FIGURES Page f 1.-Location of the study area 'in British Columbia 4...... , ...... /. .+ 3 -Loaatibrr of the study area on McKeen Ridge ...,.,.....'i;y..,.. - 6 J .\C/ 4 3.-Geologic map of the study area ...... 16' 4 4. -stratigraphic column and synopsis of geologic history ...... ,...... ,.....,...+...... 17* .. . 6- .5.-Location of the tor area ...... 46 ,,-. ' 6a,-Dist~ibution of tor types in the tor area ...... 47a I *& 6b.--~ir photograph of the tor area ...... l...... 47b C' c- 7.-Zones in a deep weathering profile and a schematic portrayal of Ehe two stagq morphogenesis theory ...... 75 8,-The formation-of weathering mantles in ~ectonicallyinactive areas ...... 98 0 * 9.-SeAematic portrayal of the'morphogenesis " lo•’-the tors on McKeen- ...... -...... 138 -8%- r & V . Photographs Page 1.-Geologic units in Ladyslipper cirque ...... 18 .i-'. 2.-Princeton sediment filling a joint ...... ,G,...... 18 - 3. -Recently exh~edtors' -west of . Ladyslipper Lake ...... :,...... ,.. 45 4.-Truncation OF the tor area by cirque walls ...... 45 . - - A -- - 5.-Single tor on the west side of'Mqeen Ridge ...... 6.. 49 if \ 6.-Single tor on the smit of McKeen Ridge ...... 49 7,----Massive-tor on &Keen Ridge ...... ,....',...... 50 8.-Ridge tor on McKeen Ridge .;:.,...... *...... 50 9. -Corestone with concentric indurated layers ..?...... , .... 53 la.-Weathering pits south of Ladyslipper Lake ...... '53 + 11.-Decomposed quartz monzonite and grus on * McKeen Ridge ...... 134 ...- ..L' 12,-Weatheri'ng penetration on the side wall - of a cleft on Giant's Cleft dome ...... 140 13.-Etching of joint planes on tors ...... '140 14.-Giant's Cleft dome .....~...... ~...... ,....:..,...... 144 15.-Decapitated tors south of Ladyslipper Lake ...... 144 - IntrhtForr - A- -~ ------This thesis combines an analysis of the morphogenesis of a tor dand- scape locat-ed on an alpine ridge in the'southern interior of ~ritishColumbia . .- . .. - .. '1 with a critical- review-of the scientific literature concorned with tors and related topics, The thesis is divided- into three major sections entitled ;I FA physiography, literatureA-reviewand analysis of Cathedral Park tors. r a - The fkst~ect~onis concerned with the physiography of the field+area on &-&en kidge and iLcludes sbbsections on the location, access, climate, soil, vegetation, geological history and laqg$oms of the field area, The -. . - current environment ~ and geologic history of the field area are examined and %* "C $ descriptions of the tors and other landforms are presented, This section -. is a straightforward appraisal of the physiography of ifc~eenRidge and no ihterp+tation of the material presented :is included. This section provides the factual material used in the analysis of the tor'landscape contained in the third (final) major section of the.thesfs. The second section is a critical review of the literature concerned with tors and related topics. Subsections within this middle portion of the h Pl ' thesis include an assessment of theories proposed for the origin of tors, t: 'A %. an examination- of the role of chemical weathering processes, spheroidal weathering attack, non-meteor ic alteratiion, petrqlogy , deep weathering, -d, climate and jointing in the production of tors, a detail of changes occurring in tors under subaerial conditions (including a separate section on ppp -- -- glaciation), and-a short'sec_tion concerned with-the problems inherent in . J - - the dating of tors. Eachpof these subsections is a discussion of a topic frequently mentioned in literature accounts of. tors. The roles postulated T, by geomorphologists for each of these factors in the mrphogeneais of tbr landscapes throughout the world.are compared and contrasted, allowing an 1 assessment to be made of the characteristic influence of the various factors -- in tor landscapes. This section provides a body of knowledge specifccally --, concerned with tori and is frequently referred to in the analysis of the tors on McKeen Ridge tontained in €he final section ~f the thesis, The final section of the thesis is an analysis of the morphogenesis +' ? - of the tors on McKeen Rtdge. It contains three subsections, morphogenesis, current weathering and micro-forms. This section is an interpretation of the' - - tors present in the field area utilizing both information directly concerned -. with the field area, and mate-rial developed in the review of the sc'ientific - literature concerned with tors. Special emphasis is pfad on detailing I' 6 how the proposed morphogenesis of these tors is in agreemelit with and ,- augments other literature accounts of tors. A smary and bibliography are presented at the end of the thesis. . .+-. Physiography Location The field site investigated in the preparation of this thesis is Q located on the sumnit and side slopes of an alpine ridge in the southern 'interior of British Columbia, Canada.f?~he site lies near the ~anada-U.S.A. I. border at 49'03'1 latitude and 1209Wlongitude.. This places the site within the confines of Cathedral Provincial Park. The Park and field area ------are located in the,,Okanagan Range, an extension of the Cascade Hountains L into British Columbia, The Park area lies in the transitional zone between the plateaus of the British klrrmbia Interior and the Cascade Bbuntains of Washington State, and between the Rocky Hountains to the east and the Coast - , 4 2ange to the west (see figure 1). The major portion of Cathedral Provincial Park lies in the basin X drained by Lakeview Creek, a mountain stream having its origin in a rugged s6ries of peaks situated on the 49th parallel and flowing for l3 dles to the north before joining with the Ashnola River, The area within the Park boundary includes th8 glacially sculptured ~akeviewvalley in which elevations 5 range from 2800-8600 fb The sokhern alpine portion of the Park is rimmed .- by the Sawtooth Mountains at the 49~hparallel, McKeen Ridge to the west and Lakeview Ridge to the east. Peaks located on this rim rise to 8500- 8600 ft with the highest being Lakeview Mountain (8622 ft) on the eastern c-~; side of the valley and Hount HcKeen (over 8600 ft) on the western side, The "i + the Park. Principal features include alpine meadows, alpine lakes and a P '. series of seven cirques cut into the easzern side of McKeen Ridge. In addition to these fe=tures found on the valley floor, principal attractions are Giant's Cleft, Smoky the Bear, Devil's Wwdpile, and Stone City, all of !em' om Inch equal8 fllteon mlh8 I Figure 1.-Location of the study area (enclosed by the emall~~tangle) in Cathedral Provincial Park, British Columbia. ' 4, . -8 I fl* -r .- / which are The of I,adyslipp& Lake and norzh of Mount McKeen, at elevations ranging from #, 7600-8600 ft. Its bundaries include the p?eviously mentioned landforms ,''* &' located on McKeen Ridge. The site can be reached by trails cut and main- tained by parks service personnel which lead to the sumnit of'the ridge I. from Scout, Quinoscoe and Ladyslipper Lakes (see figure 2). Cathedral ~&kis- approximately 140 air miles east of Vancouver and 45 air miles southwest of Penticton, ~ritishColumbia. Vehicle access to the area is provitled by the Hope-Penticton highway (B.c. Higby #3). Five miles west of Keremeos one must leave this highway to cross the . r Sirnilkameen River and drive 15 miles up the Ashnola RivqJ9 a parking ro' - area provideq'by the parks service at the northern en$ of the' Park. This latter road is unpaved, although usually well graded. All vehicles'must Y- be left at this point as no private vehicles are pdrmitted'into the Park 1 */ -d -. proper. At this point oae must hike 10 miles along a dirt rod or trail to reach the core (alpine) area 6f the Park. This initial climb is from 2800-6800 ft, and it must be, followed by an additional climb of 2000 ft along 4 miles of the previously mentioned trails before the study area itself is reached. An alternative to the initial climb from the Ashnola River is hiring Cathedral Lakes Resort Ltd. to transport person and gear from their - - -- base camp on the Ashnola River to Quinoscoe Lake. This private concession also operates a lodge at Quinoscoe Lake during the sumner months. Camp- * grounds are provided and maintained by the parks service near Quinoscoe Lake, Pyramid Lake and Lake of the Ws. Although the Park is open to year Figure 2.-Location of study area (enclosed by the.recfangle) in Cathedral Provinci?l Park. The contour interval is 500 feet. , - I - round use, thcpresence of a heayy snw pack mumally r~strirtn~~- . four or five months during the smer season. ' -2. 'Y* -< ,,.$ *, Climate i' The field site lies at latitude 49O03'~and longitude 1200- 12 r W in the 8 dry interior of British Columbia. The cllmate present in the study area is best understood, however, as a function of the altitude and exposure-of-Qe '- - - - t - site rather than being re13ted to the dry, hot surmner and cold vinter climate (~Se~penBsk) that characterizes low paits of the southern interior. The strong relationship of altitude and climate can be seen in the data of Table I, in which the stations are listed by ascending el&vation. From - this table it is evident that increases in elevation are associated with sharp increases in precipitation and decreases in temperature. This can be appreciated best .in the case of Hedley and Nickel plate Mine, which have strikingly different temperature and precipitation regimes although they are only two linear miles apart. It is important to note that although the C interior is in the rainshadow of both the Coast and Cascade Mountains, moderate precipitation does fall at the higher elevation. The Old Glory station is '&e highest meteorological site in British Columbia and lies over 100 miles east of the field area on the western flank of the Monashee Mountains. Although this station is physically distant ' from the study area, its elevation, position in the southern interior and ------location above the timberline are similar to those of the field area, The data from this station best represents the climate found on ~&een Ridge. It must be stressed, however, that the conditions present on Hdleen Ridge, which lies 800 ft higher than Old Glory station, are probably Bore severe Z& -2 ' + than those measured at Old Glory station (foe., higher precipitation, lower T 1 Table I.-Selected ciimatic data for stations in the southern interior of British Columbia. Copper Ni*ckel Prince ton "QSd Glory McKeen Ridge Stat ion Keqemeos Hedley Mountain Plqte 49O09 ' 0 Longitude . w 119~50' 120•‹05 ' 117O55 rt 9 ~ltitudc(ft) 1410 1720 7700 Mean bnuol I Temp. (OF) 49.3 45.8 28.4 Mean Jon. Temp. (OF) 25.9 23.1 11.6 Moan July Tcmp. (OF) ? 49.1 Mean An~ual . , Prec.ip. ('in. W.& Mean Dec. Pfecip. (in.) 2.7 I Mean June r Precip. (in.) 1.3 1.4 3.3 Mean frost free I period (days) I 184 158 . 17 i \ ,'t6: Mom latoat I .A spring frost -'' 12 April 4 May 11 J~ne 4 June i 6, July 4 July P Mean earliest fall frost 14 Oct. 9 Oct. 4 Sept. ' -19 Sept. 7 Aug. I 21" July I From Britiah ~olurnbiaDept. Agri. (19631, Conner (1949), Canada Dept. Trans (1967) lsnd Kendrew and Kerr (19 a temperatures, fewer frost free days), HcKeen Ridge is a north-south ridge lying over 8300 ft above sea level and l&YTVft above the local timberxine. It has a mid-tatitude alpine climate * f wicha wide range of conaitions encountered during the year, ,.*'recipitat - 1 is year round with a probable June maximum and secondary ~e6eGbermaxirmun. Po" t No month averages less than 1 inch of rainfall. Despitedthis precipitation; -- d moistme stress may be a sfgntficant and limiting factur ftsr +eg& cm . parts of the ridge, Thisq-occurs because the strong winds often present at ' I . this high and exposed alpine area blow much of the winEer snowfall off of Y' , 'C the narrow ridge, No permanent snow banks occur on the ridge and only one snowpatch was found on August 1st after a winter of above average precipi- bation and duration (winter 1973-1974). Spring-and summer runoff derived :a--.I from residual snow is qutte limited, The shallow snow accumulation suggests that frost penetration is substantial (frost penetration is inversely related to the depth and duration of snow cover because of the insulating effect of snow). At a similarly exposed site on Lakeview Mountain (at 8140 ft.), remnant ice crystals were found in a soil profile at a depth of 70 inches on August 8, 1965 by Van Ryswyk (19691, AR important facet of the climate is that frost may occur on any night 'even during the smer months, and probably -. -. less than 14 frost free days per year occur on the ridge itself. Using data from the Old elory station as a guide, it is probable that over 90 days of frost cycling (in which temperatures pass both above and below OOC) occur - - - each year, A poorly developed soil is present in the field area, The parent material of the soil is partially weathered, coarse-grained quartz mnzonite (see geology section), in which individual crystals h+ve been separated by chernical.veathering along intercrystalline surfaces .and then displaced, forming3 coarse, sandy material. This coarse soil material, consisting of - '. partially weathered crystals and lacking a fine sift or ~lay~fxaction,is e cormonly termed grt's. It is prewt throughout the field area, whi@ is ) *- entirely underlain by quartz monknite. It must be noted that the profile &:'be described below is not dependent upon lithologic coritrol because the . . - - - -+ rock has undergone a chemical alteration and mechanical weakening (described in the geology section) making it susceptible to disaggregation by current weathering process~,.resultfng in the,formation of the griis cover present today, Soils on the same quartz monzonite bedrock in areas outside the field site do not have this digtinctive griis component, reflecting the fresh, rather than weathered, state of the quartz mnzonite there. The origin, distribution and characteristics of the weathered bedrock in the field area are: discussed at Len+th in a later section of the thesis. ,+ A typical profile to be found'in the study area would include three hpfizons. The uppermost horizon is a gray to white griis mantle of individual 1 mineral crystals, 118-114 inch long, the source of which lies either in the --' weathered rock material lying below, or in a nearby area of similarly ' . weathered bedrock, This layer is 2-4 inches thick. There is no cohesioq.ip; . - w J the granular matrix, Fine materials have been removed by either percolation or runoff, leaving a homogeneous coarse layer, Individual crystals are occa- sionally covered by an lron oxide stain, and bgotite' is often partZally 4 weathered. This upper gayer is extremely porous. ~i~erpoured on t:o the surface from a one quart canteen percolated immediately into the gtomd. The pH of this granular upper horizon wae 5-6, - 6 The second horizon consists of 6-11 inches of material similar to the uppermost h& zon but including considerable amounts of sand and finer ------particles. While some fines were determined to be volcanic ash materials, most fine material proved to be smaller fragments of unweathered cryst.als or c .a weathering productg of the bedrock material. Little silt or clay is present. The fine material either:fb-d in situ or was deposited by percolating 6. groundwafer. The color is light olive brown (2.5 ~1514)and acidity 5.2. .i This zone was damp even during the late smer after a'dry period of two - weeks., being from desiccating winds and insolation by theAupper- most horizon. The color is traced to the ubiquitous iron oxide stain. The boundary between these first two horizons is quite marked. < . he third horizon is similar to the second and the boundary beween hem is quite irregular. This horizon includes sonic material similar to the second horizon in its upper portion.)ut is mainly incoherent rock. This +a -< layer was impossible to penetrate with a shovel. Occasional chunks of rotted rock cound, however, be detached (4-6 inches long). Mica is incompletely weathered. The zone is best described as a weathered rock horizon of irregular depth, probably not exceeding 6 feet. Its color and pH are 10YR/4/3 and 5.4. Underlying this horizon of rotted rock is ffesh quartz monzonite which extends for a considerable, though unknoyn distance into the earth's crust. The characteristics of the underlying bedrock are 'c described in the geology section of this thesis. e -F Vegetation - The vegetation succession encowtered in Cathedral Park from the - Ashnola River to the alpine areas' issimilar to that found in other parts * of the Sirnilkameen Valley and has been examined in detail by McLean (1969). .I t. In addition, the alpine vegetation on Lakkviewh~ountainhas been studied by ' .. e. i Van Ryswyk (1969) in his study of the alpine soils present on that mountain. * Y - t -- r: - - - -- On: porti'ons of McKeen Ridge north of the study area (on basalt' bedrock) a complex'alpine1 comnunity is present. A comparison of this corkunity ,with the * - alpine vegetation present on Lakeviewwuntain- showed them to be of similar - ,.i compdsiti,on. In view of this-similarity, the index of vegetation present a in the tundra-like upper alpine area on Lakeview Mountain as developed by . -ij3 - -9- I = Van Ryswyk (1969) will be adopted fdr McKeen Ridge. - On dry, windswept, stable sites the most common species ina tundra-like comnunity were Carex sczrpoidea, Carex hepburnii, Carex pyrenacia, Carex albonigra, Kobresia mysuroides, Festuca ovina var- brachyphylla, Luzula spicata, Trisetum spicatum, -Pea al~ina,Juncus brumnondii,-Juncas parryii, Penstemon procerus, Antennaria al+na,' Silene acaulis, Potentilla nivea, Sibbaldia - procumberrs, a%tl many others. A rather dense cover of small mosses and foliose and crustose lichens was generally preeent. * On coarser textured soils and disturbea sites Dryas octop"ctala, Salix nivalis, Salix canadensis and Lupinus lepidus var lobbii 2ncreased (van Ryswyk 1969 pg 9). * ,,,:-- .2( . - - Although members of this alpine comnunity occur in the study area, * there is a distinct visual 66ntrast as ode moves from the basalt bedrock % area and on to the quartz monzonite, Plants cover all non-rock areas on'the volcanic material. By contrast the quartz monzonite/grCs area is almost * .. devoid of vegetation. Individual members of the plant commmity occur 0 .. sporadically in the stay area at restricted sites where micro-climate and soil conditions are amenable to establishment and maintenance of plant growth. -The factors limiting the abundance of vegetation in *the stud? area * include moisture and nqtrient deficiencies in the grb, and the fact that- . it provides poor support for the characteristically- -shallow - - -- rooted- alpine plants. Plants were most often found in sheltered spofs on slopes where -a% the thickness of the uppemst horizon grt's was less..;bq three inches. t .i--. The paucity of vegetation must be ascribed to the ubiquitous presence of the griis. At similar elevations on the ?pa~t.z diorite and quartz mzonite -. - - - - - 2. t be@fbA$k,ofLakeview and l ox car Mouqtains,... the entire community is present. ;:------~o?l,qon ,wart= rnonzonite in areas other than this section of McKeen Ridge . ,* i - arq substantially similar to those described by Van Ryswyk (1969) oh c Z ' .tgpes of foliose and crustose lichen. ~ncludedin the latter we,rc ,&iden- -< t. tified varietie: of Rhizqcarpon and ~ezanora. Occurrence of these lichen , .. - r* in the study area was l&i.ted. More common and covering most eqosed rotkc' - 'P surfaces it^. the study area was the lichen Ephebe lanta. his lichen has a dull black, ha'irlike, fruticose thallus- and occurred 'in flat, thin' mats and tufts on the rock surfaces, giving the-a &k gray color when viewed-' from a distance. This lichen was*less commonly present on the gr% material, binding perhaps the upper 114 inch together. B CP It is unlikely that this area has had a substantially different vege- ' tation in post-Pleistocme times. Evidence from fos~ilpodzols ahd charcoal . - fragments o,n Lakeview Wwtain were interpreted by Van Ryswyk (1969) as /' indicatie'that the trkline (presently belo; 7500 ft) extended no higher than 8000 ft--duringme hypsithermal (6600 B.P.). Under non-forested /---- X / conditions the micro-climate of the study area bould not differ substantial-ly from-that which prevails today an& the current vegetation is probab-ly representative of the entire post-Pleisjocene period. ' Geology - - - 4. - i c The study area is located pn HcKeen Ridge in Cathedral Provinc r - British Colmbia. This places it in the/kanagan Range of. the cascadc -' I Mountains, a transition zone ,betwee the North ~askadesof Washington State 4 '/ ---- and the Thonpson Plateau of the southern interior of British Columbia. It 4 is centrally located be en"the Coast and Rocky Mountains of the$estern ------Cordilbera of Canada, The- majqr work on t-he &ologf of the area was done - P % > - ,. by H.M.A. Rice (1947; Geology and Mineral Depo.sits of the princeton Map- L I $&-' . area .$.G.S. Memoir #243), who mapped the area at scale of miles the _.r- . ' - a 4 t.2 r 2. 3 - 1 .,. - YS inch. 1nv6stigatibns of specific sites and m-ineral deposits in the map- *@. area hall6 deen d&ae by a variety of agencies and individuals. , -Y The principal geologic u~itspresent within the Park are unroofed * -- - -.granitic plutons. Limited a-as of pendgnt rocks and othcr,rninar sedtments , 1 * J - X 4- -a p '.i and volcanics are present. This contrasts.. with the &edominant sedimeqtary. t /- S + and metamorphip-ccamposition of the Cascade Mountains (~c~aggart1970) and . -= 9... I widsspread volca&Y:s of th2 British Colpmbia Interior (~olland1964). i Topographically the Park partiaLly bridges the gap between the rugged + "Y P- ~aseadeMountains of Washington State and plateaus of the British ~olumbi'a~f I 1 -a Interior. These two factbrs underscore the transitional nature of the area 1 4s-P- .. 3r . .>*? -and incidatk ;hat the geologic hi$.tbry of the park area differs significently 1 from that of surrounding- areas. The Park area would. be included by wheeler (1970) in the intermontan; , - zone at the British Columbia ~nterior,a broad zone of relatively immobile 2 crust ranging the length of British Columbia and ento northern Wa-shington .*. , - State; This zone is wehkly deformed and has undergone neglible crustal . :- * shortening when compared to +he folded and metamorphosed Shuswap complex to , 3 -P the east, Cascade Mountains to the south an& Coast Mountains to .the-west. 3 - r ,. Wheeler (-1970) suggests tliat the lack - of d&&m&&ion-may- bedue- to-the - - presence of eugeosynclinal materi?ls in the southern interlor, postulating. *- 8 that the thick, Mes'ozoic, volcanic assemblages were resistant to tectqnic dJ s stresses which produced great fo$.d6'belts and metaporphism to the eist and .$. , - w%s.t. In the Nicola Lake region to the north .of the princeton map-area, * .*,/ - - 4 9 ,-f Schau (1970)'emphasizes that the southern_portion of the intermontane zone .-- has undergone limited uplift and erosion (where compared with areas to the zez;- &* 4 . *+a south; west, and east) since the Jurassic, and was loc~lly..depressedfrom +- -L Late Jurassic through Early Cretaceous times. This great stability and . submergence during a period when most surrounding areas were emergent +- indicates t& geological history of the study area differs in many important ' a," + _r&pects from them. p --La a a - In Cathedral Park members from four geologic group: are exposed, in- ' ' eluding: sediments of the combined Bradsl~aw,Inde~gdence, Shoemaker and - . ' &+ Old Tom formations of Permian age, lava of the Upper Triassic Nicola grodp, -L Jurassic granitic pltitons, and sediments and volcanics of the Eocene Princgton group (see figures 3 and 4, and photographs 1 and 2). The r following sections deal'etl turn with each of these geologic units. Bradshaw, Independence, Shoemaker and Old Tom formatic& The earliest geologic record within the park is contained in the rocks P T of the combined Bradshaw, Independence, Shoemaker and Old Tom formations. These were identified and mapped by Bostock (1940) in the Hed.ley area and can be followed south into the Ashnola-Basin. Although these formations were separately identified in the area in which they were initially mapped, \ 4 \ Rice (1947) found them indistinguishable to the south and mapped them as a E single unit. The rocks consist principally of chert, argillite, limestone - andaandesite lavas. me fornations are younger-thaan~t:heeKozameenngroup.,< ,& of Upper Permian age (ffceugan et a'). 1964) (t+e Hozameen group is equitrifent to the CB&~ Creek series) wh6ch probably covered the entire Princeton map-area af'one time. Rice (1947) thought they may have been depoiited in part of the same basin as the Hozameen grbup but subsequent faulting, folding ,. ? 'I *. , gCw Princeton .~asalt Princeton Sediment -. Lakeview Granodiorite Cathedral Quartz Monzonite Nic :ola Andesite * Figure 3.-Geologic map of the study area ?-- t - - - -- w QUATERNARY A - pp - -A- Many advances ant5 retreats of continental ice sheets occurred in British Columbia during the Pleistocene. Only c' two advances, the Fraser and a pre- ,.Eraser glaciatipn, have been established in the interior regions. The ice _. D &- .- 'cap associated with the pre-Eraser advance submerged the field area while' the upper surface of the Fraser ice lay below the field area. In post-Pleis-e .; 1 tocene times.the area lras been characterized by alpine conditions similar to ' thdse present;%sday on McKeen Ridge. The area underwent a major uplift during the Late Pliocene and ,Pleistocene which may be continuing today. - - -- - TERTIARY Erosion had leveled the area by the start of the Tertiary and the peneplain . + associated with this denudation persisted throughout most of the period. - Volcanic and sedimentary members of the Princeton Group were deposited in the area during Mid-Eocene times. The sediment was deposited in a shallow freshwater lake and was i64 later buriedbeneath lava flows. ,- 2: w . , CRETACEOUS i.. No rock of cretaceous age is found in the field area. During the Cretaceous the park was part of a narrow marine basin situated between major areas of uplift to the east and .the west. Sedimentation in this basin was terminated 'P by a major Late Cretaceous orogeny. This orogeny was accompanied by substan- tial erosion, leaving a peneplain by the begining of the Tertiary. JURASSIC A number of granitic plutons were intruded and Cathedral quartz crystallized during the Jurassic. Two plutofls, the 3 Lak-eview granodiorite and the Cathedral quartz .I monzonite, are present in the study area. TRIASSIC Deepwater sediments and a thick laya sequence3ere deposit- -- - ed during the Triassic. Only q,small pendant of Nicola P andesite is present in the field area today. Figure 4.-Stratigraphic column and synopsis of ... the geologic history of the < - fi'eld area. 1 er basin of Ladyslipper cirque. The ing west from Ladyslipper Lake. idge crest on the left side of Photograph 2.-Princeton sediment filling a joint in the quartz monzonite. The photograph was taken near Smoky the Bear and looks to the west over Wall Creek Valley. Abbreviations for geologic units Pv-Princeton volcanic Ps-Princeton sediment C-Cathedral quartz monzonite N-Nicola andesite and ercsiorrhw? obscured the exact rezat- -ems-are+iL------.* .-- nitely older than the Upper Triassic Nicola group arrd are placed at the ~ermian/~riassicbouqfiry by Barss et a1 (1964). The combined=formations lie within the Park some four miles to the north of the field site and trend eastward in a narrow band across the lower portion of Lakeview Creek and into the Ashnola'Valley. Within the Park_ they are in contact only ~ithJurassic granitic rocks. These rocks are - , Lb the only remaining representatives of eugeosynclinal'deposition in the E'prmian Sea that covered most of the interior of British Columbia. ,Lower and Middle Triassic sediments are missing from the Princeton map-area and v Western cordillera. In other areas pre-Upper Triassic, post-Permian P unconformities have been mapped. This suggests a tectonic 1-andmass was present in Early and Middle Triassic times. The next geologic unit present and the oldest-. occurring in the study area is the Nicola group of e$eosynclinal Upper Triassic origin. Nicola Group k Members of the Nicola group are present in the study areb and are the A & . , only surviving femnants of the country rocks into which the.Jurassic plutons =.>' / were intruded. The group consists of a succession of andbsitic lava flows within which occur irregularly distributed lenses of tQffaceous and argillaceous material, and occasional limestone beds. The lava is an ------andesite porphyry with an aphantic groundmass of sdic plagioclase, pyroxene, -- actinolite, epidote and chlqrite. Phenocrysts are pyroxene (augite) and Y plagioclase ice 1947). i he group covers much of the Princeton map-area, D ,,- and Carr (1966) suggests a maximum thickness of over 6000 ft for the group in this area. The-Nicola group corresponds to the lower part of the Talka group &-- - the Talka-~aieltoncomplex of hitish Columbia (~arsset a1 1964) and has unconfo&le ++. k contacts with:-permian sediments and the Jurassic plutons in r ? . ,th&Princeton map-area, The group was formed durlng an epoch of subsidence, - A - The products of a widespread period of vulcanism were poured and ejey;ted -&at0 a'e~~eospnclineof a depth such that only fine sediments were deposited. i- t Schau (1970) suggests an environment similar to the volcanic akchipelagos of today with volcanoes alternately rising and subsiding, Sediment beds and occasional coral reefs formed around islands which reach&- tbe surface. Theyinternal structure of the group is imperfectly known as the 03casional sediment beds (which occur locally and are laterally discon$inuous) provide 1 the only recognizable units in the otherwise undifferentiated lava flows, In the type area of the Nicola group to the north in the Nicola Lake area, Sehau (1970) developed a stratigraphy for the group. The-major division he ,f. ' made was the separation of tde group into a lower feldspethic cyc1e"and'an upper augitic cycle,,*-distinction being made by noting the type of i V, phenocryst that was most comon, Fossil dating of the sedimentary units indicate a definite Upper Triassic age (cockfield 1948). The unit is extremely important economically as large mineral deposits occur within it U < (see Rice 1947). * In the study area the Nicola lavas form a 700 ft section on the north side of Ladyslipper Lake and a 400 ft section to the southwest. The group i s unconformab fy overlain by the Eucse1~ePri;rrc&olrgro~adi6fn - intrusive ce~tactwith tlte underlying Jttrassic+ukorr. It could not be - ascertained where within the stratigraphy the pendant liesi The predominance of pyroxene pheaocrysts in the hand specimen, however, indicates the section bglongs in the lower (~iddle~orian) part of,the group (following Schau 1970). The limited exposure of the lava, absence of sedimentally-- - strata - - --wiihin itt - I< and inability of determining the present orientation of the rock (it has undergone several episodes of folping) precludes more that this tenative assessment of what portion of the eriginal strata is present in the study area today. . 1% No 'sedimentary stratum of the groupoccursin the study area. No flow 9 structures could be discerned and the ex6sure is a series of undifferent- . -- iated, highly-fractured, lava flows. The base of the unit is a recrystal- lized aureole zone (due to contact with theJurassicL-plptonh-. which grades . slowly into .unaltered lava. Alteration could be diskinguished in hand specimens -over a 50 foot vertical section. Samples near the contact-have a gabbroic appearance and texture. The actual contact of the pluton and & * Y 'lava is obscured by talus material and 5ts location was estimated by noting a where granitic material disappeared from the talus. Two hand spe imens /!- /!- - taken from the talus ;bowed both granite and altered andesite, indicating a probable sharp cptact between the rock units. The unii om composition of the plutons, lacX of bassc inclusions and apparenz sharp contact suggests magmatic emplacement ('perhaps as a-hot plug) rather than granitization. The lava commonly has a dark gray to black aphanitic matrix, with pyroxene and plagioclase phenocrysts up to 1/16 inch-long, the former being the more common. The pyroxene (augite) phenocrysts have often been spb- stantially weathered on ekposed surfaces, leaving 6mall iron-stained cavities. Weathered surf aces have a-Eghf brownixTiieC color due -toTiiFn-p-p ff - continuous, mottled iron staining. Alteration .i;s-prcs&t m-af.5-exposed and joint surfaces,and to a depth of slightly over 118 inch. Only a few fresh faces were found on recently shattered mSteria1,and even these showed -. some signs of incipient weathering. - +The Nicola group has undergone three periods of folding, major intru------ % '. , - sion and major uplift. The rock is very closely jointed and exposures d , have a shattered appearance. The jointing is irregular although some major 0 0 lineamknts in the granite (striking N 60 W and N 25 E) werg traced through the lava. The Micola lava is the source of most of thg. talus material in 0. *. Ladyslipper cirque. Current exposures on cirque waUs and on the ridge > > 2' separating Ladyslipper Lake and Pyramid Lake are no older than the ------* -* - LL- - * t Pleistocene, --4. 't The Jura&s+icand the Cretaceous b I. .G~' No Jurassic strata occur in Cathedral Park or the Prineeton mapLarea. 5- Cretaceous deposits lie unconformably over the Triassic, Springer et a1 . *, (1964) indicate that epicontinental seas covered the present day British Columbia Interior through most of the Jurassic, Deposition was in a / .. * -. shallow sea marked by dirferential uplift and subsidence. Freebold and, Tipper (1970) sdthat areas of the present day interior and We~tern ' x Cordillera were Astable throughout the Jurassic and that there \?ere at -% least two major tectonic events. It is probable that some -Jurassic. . deposition did occur in the area but that all sediments were removed before the Cretaceous. The major geologic event during the ~utrassicwas the intrusion of granitic batholiths that began in the Middle Jurassic and continued into the Cretaceous. Uplift was doubtless concurrentA with Two different granitic plutons occur ik the fikld area. The contact of the two .runs slightly to ihe south of ~ad~sli~~erLake, trending west- northwest. To the north of Ladyslipper Lake is a fine-grained granodiorite A - - - named the Lakeview body by Rice (1947). Amphibole needles characteristically & ------occur in groups in this rock, giving it aglomeroporphyrytic texture and distknctive appearance. In the area near Ladyslipper Lake this body is , - pobrly exposid due to overlying Nicola lava and talus material. Some out- . . crops do oc=ur on the north shore 'ofj. the lake. The+contact of this unit d with the Cathedral quartz monzonite to the south is. obscured by the lake, talus and glacial deposits. ,For this ;eason the cokact shown on fi&e 3 7- is only.an estimate of the actual location. -Rice (19471 reports that to the east of the lake the contact is well exposed and that the Lakeview grano- diorite is apparently intrusive against the Cathedral quartz monzonite. 2 CI The other intrusive body was first recoghized and named by Daly (1412) I the Cazhedral body. Rice (1947) included this in his "redv1 granodioritd \ grouping. Daly. (1912) reported the body to be a coarse-grained biotite - 5 granite and found it to be +singularlyhomogeneous both in texturq and mineralogically. He collected a type speci,men on the Comission Trail near the top of Bauerman Ridge, about five miles to the southyest of Ladyslipper Lake in the U.S.A. A chemical analysis of the specimen was done by M.F. Connergf the Canada Geological Survey. The results of this analysis- are given in Table 11. This rock type is more accurately described as a quartz monzanite rather than a biotite'granite. The date of the emplacement of the Lakeview and Cathedral plutons cannot be determined stratigraphically because of the lack of Jurassic sediments. Near Hedley a potassium-argon date of 156 m.y. ------ B.P. has been obtained for the Similkameen batholith (~oddicket a1 1972). - This mi&-Jurassic date is probably close to that of the Cathedral body as the intrusion of these plutons is thought to .have been synchronous ice ~ablk11. -Chemical analysis of Cathedral quartz monzonite. Dominant phase a*ysis Calculated normal QTZ . 21.62% corundum Fe203 orthoclase i FeO albite ' - -- - MgO -anorthite CaO apatite IL 0.22 ilmenite MT 0.26 magnetite H20 above EN 0.92 enstatite FS 1.97 ferrosilite H20 below 1 .. Total 99.95 . *. --J - From Maxwell (et a1 1965) 0.16 The specific BfBvity'was 2.621 and modal composition; microperthite 40.3% quartz 35.7 r MnO oZigoclase 11.0 " &hoclase 7.0 '; biotite 5.0 Total minor amounts of apatite are ptesent along with rare zircon, * b Fzom Daly (1912 pg 466) - -. From Daly (1912 pg 460) .ti Daly (19129 noted a younger pha striking N 60O~from Bauerman Ridge into the Wall Creek basin. -The younger phase strikeas, parallel to a major joint set in the quartz monzonite, & suggesting it was intruded into a contraction joint of the main mass. The body is more silici'c than the mass of the Cathedral body and lies'at the closest 1,112 mile; f'rom the field area. .y- '.& .* :-* ------L - 1 -- - The quartz monzonite in the field area is a homogeneous, coarse-grai-ned - rock with individual crystals up to 3/8 inch long and of composition as given in Table 11. A basalt dyke striking N 25O~cuts through ;he *rakite r in the study area and is approximately 10 ft wide, ~a~idweathering of * this dyke -has resulted in a break in the granite forming the deep vertical * chasm (~iant'2 cleft) that is a major attraction of the ridge. NO-other basic 'dykes are present. Minor siliceous veins occur within verticiil joints in the field area and appear to be small-scale joint fillings. These veins - _I terminate in some casbs against other joiLtg while in others they disappear beneath the griis cover, All observed were 1eis.than., . 2 inches wide. \s /c Typically they were extremely fine-grained and lighter in color than the a * host rock. They of ten.'protrude from the general rock surface and apparenxly have a greater resistance to weathering than the host rock. . . - '~ The major jointing in the quartz monzonite.is an extremely well - :v developed set of vertical joints striking N 60'~and N 25O~. .These joints occur at iqtervals of 5 to 20 feet an expased_hedro&-onXcKeecRidge,-Ic-e -- - attack in the cirques of Ladysl ipper Lake and theSawtooth Range exploited these fissures and left near vertical faces of rock in-some cases over . 600 ft high. It is probablk these vertical joints are tensile fractures which developed during the Pliocene uplift of the area, Non-vertical joints are of two type~.~Mostcommon are planar low-angle joints of-irregular ------pp-p -- - - strike. he siliceous veins mentioned above a+hot occure in these joints. This indicates that the horizontal jointing is of later origin than the 3 vertical joint system, perhaps having formed subsequeqQto removal of the - overlying country rock in a near surface environment. Less conkon were curved joints in areas where the rock assumed the shape of a broad dome. -' &.' These occurred independently of the low angle planar joints -@gl appeared to die out both laterally and vertically in the case of the largePdorne that 6 is tru&ated by Giant's Cleft. No examples of post-Pleistocene extension (exfoliation) fractures on glacier-seufptured cliffs and yalley walls were observed. , e The incomplete exposure of bedrock precluded a detailed assessment h. @ of the densitpand brientation of joint systems in the field area as it was -ir- - 6= impossible t~festimatethese factors in griis mantled areas. A quantitative d. d. 8 1- ,1 4 analysis of j *irking would necessaril~have been hampered by the incomplete exposure of bedrpck and w&ld have been characterized by a biased sampling procedure, precluding useful interpretation of the results. In those apas where bedrock was exposed within gr$ covered areas, however, joint frequency I *- seemed to be substantially the same as in tor areas where the grk was entirely absent. '" * No Cretaceous sediments are present iq Cathedral Park, although they % * '- %A do occur at lower elevations in the l?rinSeton map-area. The earliest Cretaceous record in th_e_prieceton gap-area ik-that of marine deposition-in . ---- >. . ,A". - the Dewdney Creek group. The marp-area was apparently included in a narrow -t ------sea that existed between the Coast Range uplift - to the we&- and the Nelson X. uplift to the east during the Lower Cretaceous (~udkin1964). The deposition i' 8- became deltaic and then continental during latkr portions of the Lower 7 -. -.- Princeton map-area. ..Material contained in sedimentary strata indicates ' 5, that exposure of some Jurassic granitic plutons began at this time. The ,' 4 original extent Q•’ these Lower Cretaceous sediments is not known but they. are inferred-to have covered most of the Princeton map-area. No Upper Cretaceous haterials are present in the field or map-area,although a map P by Burke and Williams (1964) indicates that they believe limited con6inental - deposition may have occurred during this time. 1 -,f .:.a .:.a A major mid-Cretaceous orogeny terminated sedimentation in the map- .+.+ -- area ajd was marked ,by thrust faulting throughout the Cascade ~ountans -.^_'-p -3 1 . 3- -.* (~cTaggert1970). Twenty five miles to the east of Cathedral Park a-thiust fault brings the Permian Eozameerrstrata into contact with Lower Cretaceous Dewdney Creek sed.iner$s ice 1947). . .Erosion following this major orogeny removed most of the sediments from theftield area, exposing the underlying .- R - pluton. By the Paleocene a low relief erosion surface was probably present. - Willis (1903) suggested the accordant summi %P='of the Cascades are-indicative - - -- of this Early Tertiary surface, and Holland (1,964) states that-the high * -2- b t peaks of the Okanagan Range represent remnants of a now elevated and dissected Tertiary surface. He includes Lakeview Mountain as one of these.- peaks. - -The surrunit areas of Bozcar Hounta'in, the Sawtooth @nge and McKeen Ridge may also be remnants of this-Early Tertiary surface as they have elevations + similar to Lakeview Mountain. T. + . + - - --- A- -- A- This orogeny and subsequent erosion left 9 stripped, low relief surf ace in which the overburden was removed from above the granitic plutons *- - $ e exposing them at the surface. y % \ *. Be Paleocene is marked by an absence of orogenic activity and it is $ probable that erosion continu'ed unabated, fhrther extending and bevelling a the peneplain. This continued until Middle-Eocene times when lavas were - 6 extruded on to this low felief surface and sediments deposited in local basins. These volcanics and-sediments were deposited within the same time period and together comprise the Princeton group. Both volcanic and - 1 sedimentary members of the group are present on McKeen Ridge and they piay *"a significant role in this thesis. . ' The lowest member of the group is a volcanic agglomerate of.approx- imately twenty foot thickness. The unit has _a:blo=ky, uneven appearance and - .. forms a distinctive rim around the upper Ladyslipper cirque. The rock has .a fine brown matrix in which are embedded numerous pieces of lava, and red, yellow and gray pumice. The lava and pumicearecommonly vesicular. - P d 2; 2; This volcanic agglomerate has the appearance and characteristics of a \- lahar deposit. - 7. The volcanic agglomerate is Fncluded in the Princeton group for twp = - 1. reasons. It has a limited aereal extent and terminates abruptly against the <. ' Nicola lava i~ the saddle west of ~~rami$-'~&nt~ain.Its character is - i ' 'radically different fgqm thc depositional conditions associated with the > * /. I Nicola group (lava and deep water sediments1,and it shows no signs of the extensive jointing (and probable foldink)'-present in the Nicola lava. Rice (1947) rnakcs no menrion 03 a unlt Cif tlizs €$piZ in tke-coTaZ'gkaup but -- ' . . 4- in his mapping,of the area included this-dqosit in the Nicota grab. It . - - "F* .. is ~robablethat the narrow deposit of very Limited extent was not-noted as %* it is of little significance in gcologi~~mappingon a scale-+of four miles i- - > The agggbperate has a massiue 'structure ad-a-FS-~O be eafOFHlab4y overlain by the Princeton sediment. Its massive structure (unjqin~ed) makes i; resistant to weathering agents under presenC conditions. ~otonly -d,. does it stand oGt as a prominent rim around the upper basin of.Ladyslipper r r cirque,but large pieces 10-20 ft tall have survived intact, sliding over 0. 400 vertical feet into the upper cirque basin where t'hey form peculiar up- standing bloclcs. The agglomerate has a distinctive, rsugh appearance in weathered exposures. ReRoval > the matrix material is eff$cted more I rapidly than the breakdown of the lava and pumice inclusions, and the latter -1 project irregularly from the rock surface: Pieces of pumice similar to that embedded in the agglomerate were -, .> 'h found to the south of Ladyslipper Lake on the Cathedral quartz monzonite. %- These pieces either indicate a former extension of the agglomerate into * this area or glacial transpoa of-,the material southward .from the present '2- .. outcrop. The latter explanation is regarded by the author as being the more likely as the material was found at elevations .below the Gobable maximum extent;of tWe .Pleistocene ice sheet. Subsequent to the deposition - 3 of the agglomerate,-the basin was apparently damned (possibly by a lava -r. r flow or mass movement associated with the vulcanism) creating the small a, -y. body of water into which the overlying hinceton sediments were deposited. *I. Overlying the Princeton agglomerate is first a fossiliferous sedimentary brecc3a and then another lava layer. Ther upper lava is the youngest ------geologic unit in the Park and is anapha&i;-basalt lacking phenocrysts. It is thus readily distinguished from the Nicola lava by the absence of augite phcnocrysts , and a uniform reddish weathered appearance rather than the mottling characteristic of the Nicola lava. The major-joint 1inarnentG~oundin the Cathedral body and extending into the ~icolalava J B & are absent from this Princeton lava, More e3idence of active,frost shattering - --1 ---* in fresh rock faces was found on this vofcanic unit than the Nicola lava. This heightened susceptibility to frost attack GeHults from the greater e- 'exposure and the absence of closely space&,..open jointing on this unit, In the area above Ladyslipper Lake named ~1'sWoodpile, columnar structure 'rk is well developed in the Princeton basalt, the contorted columns reflecting , .&+ * uneven rates of cooling within sthe flow. h - a- Interposed between th~?lava units is a light gray sedimentary breccia. The matrix of the breccia is a fine sandstone, although occasional silty - lenses occur, Withing this matrix are embedded angular fragments of granitic - + material up to % inch long, occasional pieces of purniee and basalt, and many single crystals similar to those which form the grzs horizons present today. -- * The granitic fragments and crystals have their source both in the Cathedral -> .* quartz monzonite and the Lakeview granodiqrite, although most is derived from the-former unit. None of these fragments show evidence of rounding, indi- .eating that they. were transported from a nearby source. Moving to the nbrtk, away -from the Cathedral pluton ,fie amount of coarse material decreases and d is- - - .'clean sandstones may be faund. The frequency of fo~'s5.1~in the"sediment also * showed an apparent increase to the north. This fact, combined with the ' decline in angular material and thickening of the bed to the north, suggests .c - the quieter water was present in this area (~uiniscoe~ake) and that the source of material and delta was in the southern part of the unit. The + C 3- breccia currently exmds as-a continuous anit- -keRtQttiReseoe-•’,&-Lady- - - - /- slipper Lak~. .The sediment was also fougd 5 mile to the south Q•’ Ladyslipper Lake (see photograph 2), indicatieg ehat the sediment formerly extended farther.to the south than its current terniinus west of Ladyslipper Lake. .. . * r This suggests that the sediment covered-the ent$~efield area at one time, lack of well defined bedding,' irregular lenses and poor exposures of the ------iment made it impossible to identify individual beds, and difhcult to determine-the orientation of the unit. Most +sures have a shsttered > % layer of rubble over their surface and are partially covered by P.basalt talus. The bed has been gently tilted, dipping OW and having a strike-,o'f N 15O~. The cement-iscalcareous. c * This sedimentary breccia is fossiliferous. Fossils were collected near ,k - - ' Giacier ~deand identified by ~eil(1947)' of the Canada ~eolo~ical~~u~ve~. These included Sequoia langsdorfi, Equisetum similkamense ~$/Trochodendroides arcticum. Specimens of each of these were collected during field work for * * Y the thesis. Equisetum similkamense is an extinct variety of horsetail not previously described before its discovery in the Similkameen Valley by G.H. Dawson (1879). The fossil Sequoia langsdorfi is also extinct but is a common member of Tertiary collections. It is most closely'related tq the 0 balding cypress of today (~erry1926). The remaining fossil, Trochodentroides %..* .( arcticum, was assigned to the Cercidiphlaceae by B+ wn 1939) and renamed - Cercidiphyllum arcticum. The only remaining member of this formerly wide- <. <. spread family is the Katsura tree of China and Japan, None of these fossils are "index" fdossils suitable for thi accurate dating of the sediment as they are comon members of Tertiary collections. Volcanic members and sedimmts of the Princeton group occur throughout the Princeton map-area (including workable cod near princeton). More fossil types were obtained-from.- these sites without resolving the.question of the - age of the group, estimates ran$ing from Eocene to.Miocene. J.W. Dawson -- - (1879) judged the flora collected from what he called the Similkameen beds * - to be of Upper Eocene or Cower Oligocene age. Bell (1947)'though the fossils b which he collected to be of Upper Oligocene or Lower Miocene age, while - Carpenter (1947)-.regarded fossil insects he examined-- to be clearly Tertiary - - - p--p-- and probably Oligocene or Miocene. Russell (1935) thought a mammal tooth found in the Princeton coal beds to be provisionally Trogosus minor of the rr 4 order Tillodontia and assigned it a mid-Eocene age.; Iri the face of this conf 1ic ting evidence Rice ( 1947) concluded: Some conflict, therefore, exist in attempts to fix the age of the Princeton group as between the evidence of fossil plants and insects and that of.fbe mammal tooth. There is a bare possibility that the Princeton coral. bash contains sediments of both ages, separated by an unconformity that has not yet been recognized, but this explanation is improbable. The final solution of the problem will have to await further study; but in view of the cumulative evidence of the plant and insect material that has been made available, the younger age is provisionally accepted ice 1947 pg 31). Gazin (1953) reassigned the fossil examined by Russell (19351,and an a additional jaw fragment, tg be Trogosine tillodent fossfls of Middle Eocene - * age. Rouse and ~athe"s.(196l), in an attempt to res'6lve the disputed age, obtained a potassium-argon date of 48 m.y. fr0m.b-iotite'taken from an ash .tp,P% layer, placing the unit squarely in Middle Eocene time. Hills (198i) has J > 4 examined the 'microf lora of the Princeton coal field and accepting the date = .l 3 "of Rouse and Mathews (1961), suggests it.could be used as an index collection . for dating other microf lora collecfkons. In a qeries of 15 potassium-argon -*.,* '+ - dates obtained from the ,~i$n&ton group, Hills and Baadsgaard (1967) con- -9, firmed the single date .obtained by Rouse and Mathews (1%1), suggesti* a 4" - mid-Eocene age of 50 m.y. for the ~rinzetongroup. The Princeton group occurs in widely separated sitesq fn the Princeton ------map-area which are regarded to be local areas of deposition rather than a general sedimentary cover. Assuming that the widespread occurrencc,pf lavas of similar composition and sediments-containing comn megafossils do, in 1. fact, represent synchronous deposition, the Pi-inceton sediment above ,Ladyslipper Lake can be 3ssigned a Middle Eocene age. Q b - - ,- -e Evidence of the paleoclimitic conditions prevailing during the depo- sition of the sediments has bqen inferred from the fossil types collected. .* 7 ,/ 5 1 Of the thrike fossils collected by Bell above Ladyslipper Lake; J.W. Dawson (1890) states that Equiseturn similkamens~grew in wswamp,or $ond environ- - '3 C ment in association with leaves from coniferous and flowering plants that -' would drift or be blown into the water body. Brown (1939) states that ------Cereidiphyllum arcticum would be associated with low altitudes and warm, temperste environmedts. -&ll (1947) reports of the fossils from the Princeton group which he examined that: , The climatic conditions indicated by the flora are warm, temperate, with ahndant rainfall at least in the surranerf months, and a con- siderable degree of relative humidity ell 1947 pg 30). " The sedimentary breccia was, therefore, deposited in a freshwater swamp or \ z< other small body of water under certain humid (th; *incomplete uplift of the I Coast Mountains, implies the absence of the rainshadow effect and considerably wetter conditions) and possibly relatively warmer climatic conditions. This climate is similar to that proposed by Hoplcins (1969) for the Eokene - e-, ? Kitsilano formation fn the Vancouver area of ~ritisk'~o1umbia. The climaLe was certainly mid-latitude, probably more equable than the #bate present today, but not tropical'or subtropical. The general topography of the area . . 4 was a low relief su$%e with the present day McKeen Ridge area occupying C a topographicJow area. The Princeton lava flowed over the sedimafft bed at . -4p a later date, protecting- --- -both- - the- - sediment-- and underlying-- granitic rock from subaerial attack. This basalt armor cotrored an area much greater than. ------indicated by the current exposure. The contemporary $opography position of HcKecn Ridge in part has resulted from the lava cover ensuring that this area was reduced more slowly than the surrounding areas. ------No Turther stratigraphic unit is present in the Park. Evidence from other parts of the Princeton map-area suggest the area underwent an episode of mild deformation and erosion as subsequent~~ost-~iocene)basalts were r *L extruded over.- a dissected surface ice 1947). 'The major uplift of -th6*2qea 9 2\ O' occurred duringiPliocene times. The orogeny that produced the Cascad"e,-. , . - Mountains is considered' bf>hickin and Cary (1965) to have begun and continued through the lasE si;q-miTlionyears, Holland dates the most upliftp- - - r of the interior plateau as Pliocene. Mish (1964) considers the major uplift U of the Northern Cascades to pre-date the Pleistocene. The initial uplift 1 of the field area occurred in the Pliocene, with orogenic movement continuing a into the ~leisto~ene.Modern drainage patterns and the gross topographic features of the current relief were established prior to and during this^ uplifband were present before the onspt of Pleistocene glaciation. The Pleistocene period will be discussed in the immediately following sections on glaciation and landforms, Of interest as a final geologic deposit is volcanic ash material (glass and glass encased phenocrysts) present on McKeen Ridge and Lakeview Mountain. Van Ryswyk (196y) did extensive work on the alpine soils of Lakeview Mountain and found that ash :c* constituted a variable,'but significant, portion of the,fine sand fraction of soil samples he collected. He found ash prgsence to be a useful criterion for distinguishing soil types and variations, Platy, tubular and vesicular, glass! shards were found along with glass encased phenocrysts of orthoclase, ------1 - -- plagioclnse, hornblende, magnetite, hypersthene-and augite. The refractive -- . %l indice of the glass was determined by 0kazaki (cited by~an,~~sw~k1969) to be 1,492-1.498 with a 1.496 dominant for the upper horizons and a range 1.499-1.502 for B horizons. Van Ryswyk did not identify a source for the ashfall, suggesting.only that probably more than one was represented. Other , ", ------than, identifying ash material in soil samples taken, this writer d,id no t .a .a ------further analysis. d " 4." After examining the ln-erat;reLconcerned with volcanic ash deposits s in the Northwest U.S;A. and Canada, this author believes the source of the ash present within the Park caq be estimated with reasonable certainty. Ashfalls occurring in the NW U.S.A. and Canada are listed in Table 111. 7 ' Table ILL,-Post ~@~s_to&e ashfalls in the NH U.S.A. and Canada. -- r-- . Ash source Date Reported refractive indice ' ' of glass -. .m I Dominim t Range Glacier Peak 12000 B.P. 1.495-1.497 1.49i-1.500 Mt. Mazama (crater ~ake)' 6600 B.P. 1 504-1.. 509 Bridge' River 2300-2400 B.P. 1.499-1.503 4 Mt. Ranier C St. Helens Y St. Helens W f St. Helens T 1800 A-D. 1.48 -1.50 - From Crandell et a1 (1962), Nasmith et a1 (19671, Okazaki et a1 (1972) and Wilcox (1965). The known distribution of these ashes suggests that the Bridge River (Nasmith et a1 1967), St. Helens T (~kazakiet a1 1972), St. Helens W (~asmithet a1 < 1- 1967) afid ~t,Ranier C (~ilcox1965) are pot likely to be present in the / ., I' 7. Z ------Park area, Of the remaining ashes the Glacier Peak ash extended in an" easterly plume that is marginal to the field site and the St. Iielens Y ash occurs in a narrow prurne sweeping northeasterly into the. British, .Columbia Interior (~asmithet a1 1967). The Mazama ash is comin throughout the ------Northw~ter-neat- and British CoImb-La,. We-&ate 0i.f the GLacier Yeak ashfall at 1200 B.P. places it near the maximum advance of the Sumas Stade. during which heavy alpine glaciation was certainly present in Lakeview Valley. This fact and the observation that the study area falls outside of the known limits of twlume make it an unlikely source of ash. The r presence of augite phenocrysts is significent becaus2'they occur only in the - s a -+. Mazarna ash, the presence of _cLinopyroxene being one criterion f ox-dist-ing- -e uishing between the Glacier Peak and Mazarna ashfalls (~ilsonand Powers = 5 1964Iland by the same logic the Mazama and St. Helens Y ash. The range of , the refractive indices (1,492-1.502) obtained on Lakeview Mountain glass falls outside th& associated with the Mazma glass (1.499-1.512) (1.504- 1.509 dominant), and the predominant 1.496 value corresponds poorly with that of the.Mazama ash. This indicates that one other ash is present. The refractive values for the Glacier Peak and St. Helens Y ash would both supply the range, and dominant value needed. Phenocrysts of the amphibole cwaningtonite would conclusively confirm the presence of the St. Helens Y 6 ash, but the absence of the same cannot-be taken as proving the absence of the ash. Mechanical disturbance of the upper soil horizons by solifluction and " frost actipn has eliminated any stratification in the ash. The change in the refractiqre value of'the glass with horizon change is of questionable . significance. It thus seems likely th t. two ashfalls are present, the k: Mazama ash and the St. Helens Y ash,with the possibility that some Glacier - - - Peak ash or other ash may be" present als'o. 9 Pleistocene The ~leisfoceneperiod is the interval beginning 2.5 million years age and ending about 10,000 B.P., that is characterized by ~limatic'chan~eon,a .e,* i 1 ... ------worldwide -scale. ~n North -&erica climates became significantly cooler ------i" - - response to which great ice sheets formed and covered much of the continent, Fluctuations in the climate broughLabout- at least four known major advances 4 and retreats of the great Laurentide.ice sheet. In the Canadian Cordillera - a lack of thorough study and more complex conditions have resulted in only the final advance being well documented. This advance, callid the Frayr glaciation, is correlated with the Wisconsin I1 advance of eastern North - - - America. Minor fluctuations within this most recent major advance have *\ been established onl; in peripheral areas (see Armstrong et a1 1965). In the Interior Plateau region of British Columbia, coalescing mountain glaciers resulted in an immense ice sheet and dome which submerged almost the enttte land surface of the interior. Although major topographic forms and drainage patterns were established prior to the onset of the t* Pleistocene, glaciation has substantially altered the landscapes, leaving major and minor erosion and deposition features. The depositiqnal forms present today are almost exclusively the. result of the ~raser.'glaciatio~as features developed during earlier glaciations- were generally removed by ., the advance of the Fraser stade. A result of this has been the' tendency of workers in the British Columbia Interior to discuss glaciation only in terms of the Fraser glaciation and neglect possible- earlier and greater advances, In.the southern interior this has resulted in widely varying estimates of the maximum depth of Pleistocene ice sheets. In many cases this can be resolved by attention to whether the miter isspeaking of a- Fraser glaciation or an unidentified pre-Fraser glaciation. In British Columbia the existence of evidence of widespread glaciation 1 was first grasped by G.M. Dawson (1881, 1891) whqdcspite some influence from - the then popular theory of marine submergence, grasped province wide glaciation and compared it to the ice cap currently covering - - -- the interior of Greenland. The actual of growth and extension of the Frascr ice m%s in the Interior has been discussed by Mathews (1944) and Tipper (1971)lagd can be divided into four disfinct phases including: 1> Alpine stage: ice accumulates in mountain areas at -the onset of glacial conditions. Valley glaciers form which move down existing gradients, Inrense alpine stage: valley glaciers coalewe, crnss divides and move against existing slopes, An ice cap forms over the mountains and ice moves toward lowland areas, Mountain ice sheet stage: ice covers all but the highest peaks in mountain areas and the associated piedmont glaciers in low- land areas coalesce to submerge all relief, The ice sheet in the lowland ar,ea is not independent of the underlying topography, Ice dome stage: an ice sheet is domed over the Interior Plateau and moves outward radially from a central ice divide. (adapted from ath hews 1944 and Tipper 1971). c, ev -6 This sequence is a logical estimation of the sequence of glaciation in mountainous terrairqand in the absence of field evidence to the contrary, can be adopted for the British Columbia Interior4-' Deglaciation is thought to have occurred as a combination of marginal retreat, downwasting and stagnation. Tipper (1971a) concludes that evidence in the dentral interior indicates a pre-Fraser glaciation, a Fraser glaciation and a limited post-Fraser - glaciation. Only sparse information is available concerning the pre-Fraser glaciation as latee ice advances destroyed, buried or otherwise. obscured evidence of prior ice advances. Nasmith (1962) describes pre-~ra$ersand and gravel materials discovered from c~re-specim~nsb~eneath~Fras-e~:p.lacial~~- --- lake sediments in-- the Oltanagan Valley,and concludes tkt - portions- of the valley were more deeply eroded by a pre-Fraser glacial advance than the Fraser advance. Tipper (1971b) cites evidence of-erratic boulders that cannot be reconciled with known Fraser or post-Fraser ice movements and d'--- / - c 4 - i s. .. + _ smarizes other evideke from thk Rocky Mountrains -which indicates the + ------former presence of an ice sheet of greater extent than the Fraser advance. ?* - =* From the admittedly limited information summarized above, he concludes of )L >this pre-Fraser glaciation: . . / a) that ice flowed radially from an ice dome in central ~ritish Columbia b) that ice flowed over and through the encircling Coast and ,. '. ' Rocky Mountains c) that this ice was thicker and spread farther than the Fraser 5 ice. sheet; ice must have been considerably thiewr to havk overridden the Rocky ~ouritainq;(Tipper 1971b pg 561, The extent of this pre-Fraser glaiiation is of considerable importance % and interest in this thesis, Rice speaks of ice "thiclc enough to erode the tops of mountains as high as 8600 feet" (~jce1947 pg 4) in- the Princeton *. 4-- ma9:area. He states that the principal flow within the sheet split into - two lobeshear Princeton,ode of which moved southeast to parallel the lowee -,-i* *g Simillcameen V&lley, and the other which moved south and southwest into--. 1 *> q, y. ~ashin~toib~tate.between the Tulameen and upper Similkameen Rivers. The - ;, - field area'7 is located midway between these two-active channels of movement within the ice sheet, and may have been in an area of relatively slowly moving,. inactive ice. Prest (1957) suggests that ice in the Okanagan Range -, was thick.enough to override obstacles up to 5500 ft during this pre-Fraser glaciation. Holland (1964) states that the soutkern' ~nterior' Plateau was occupied by an ice sheet that was in excess of SO00 ftwhile the glacial a maps of Canada (see Prest~ta1 1953, 1968) show an upper ice surface under 8500 feet, ------4 - 1 Durin~his field uadc this writer spent some time determining the >, "=.: -:' upper exte&-of glacial erosion in LakeV4ew Valley as this is of considerable 0 importance in assessing the origin Ad morphology of landforms present on McKeen Ridge. The jagged appearance of the Sawtooth Range at the head of * -, *- - - .L L - - & d . ~akeview~~~lle~suggests that the area was never completely submerged beneath - - -- I--- glacial ice. Their rugged form cannot be reconciled with the bevelling and smoothing &tion of a continental ice mass. Both Lakeview and Boxcar Mountains have the gentle, rounded appearance typical of peaks which have been overrun by glacial ice. This apparent glacially ~culpt~redforinis' deceiving as they are of similar material and height as the jagged Sawtooth Range. Their rounded form is unlikely to be the result of glacia~.action,but, more probably +reflects their position as remnants of-a Tertixrry low- r+Li& /' surface (~akeviewMountain is ~egardedby Holland (1964) to be the remnant of gf$$leogene monadnoclc), The actual upper level of the ice can be estimatgd with rea-sonabled certainty. Ice has'flowed between Lakeview Creek Valley, - Ewart Creek v$i1ey and an unnamed tributary valley of Ewart Creek Valley., This flow has left distinctly.+- WU"shaped gaps between Lakeview ~~untainand Boxcar Mountain, and between Boxcar Mountain and the Sawtooth Range. The , % curve of the valley 'profile of the first valley changes abruptly above Phe 8400 ft contour, abandoning the regular curve of a glaciated valley for a < low-gradient slope. The upper level of the ice can be judged tro have been no lorfei. than the 8400 ft cbntour, near this break in slope. An ice surface at this level would-have left only a minor portion of the study area t / ..- and McKeen Ridge above the ice surface, , Trim,;&ines associated with valley glaciers in the Lakeview,: Ewart and Wall Creek basins (valley glaciers are- . tho&ht to ha& been presqnt during wa-ning and waxing stages of continental glaciation) occur at elevat,ions in the 7600-8000 ft rangtt. - t 7 '% The pre-Fraser ice sheet- moved- southward through the study area. AS'- ._ ,-- / .-. noted earlier, the major zones of flow within $,he ice sheet were located to either side of the prcsenf day park a'rea. . Flow within the Park area was in- all probability not markedly aggressive, Bnd the amount of erosion effected . - - 1 f in the area may have been limited. Dolmage (1934)contendsthe lack of ------erosion in thePrinceton basin reflects stagnation of the ice mass due to' the damming effect of the upward slope-.to the south, More significant as 1 t, 1 ero~ionagents were the alpine glaciers existing in the valley d&ing the 'I c incipient and waning phases of each major glacid period. ' - f. The Fraser glaciation reachedrto lesser heights than the pre-Fraser & glaciation. Tipper (1971b) states there is no evidence an i-ce dome developed sr,- . Q- -A w Z , n over the British Columbia Interior during the Fraser glaciation,and that the ------_____--- - stage of development reached might be described as an initial continental ". %+- ice sheet stage that uas terminated by deglaciation. This ice mass nev"& ar / L c- - became entirely free of tHe underlying topography. Although the piedmont q glaciers coalesced to cover the entire interior, they did not reach ice . dome proportions. This conclusion is based on the judgement that the I . 8 B deglaciation features and sequence arc not compatible with the hypothesized - C ' behavior of a shrinking ice dome. The Fraser--glaciationwas by all accounts .L C-'' k of lesser extent than an earlier advance, Prest (1957) suggests this ice a, .* did not reach 7500 ft in the Okanagan Rang3 and Sprout and Kelley (1961) '+ '+ agree with this 7500 ft level in the Similkameen Valley, As has already been noted,the ice of this advance did not act'as aggressively as the pre-Fraser ice sheet. Periglacial features are found in the vicinity of Ladyslipper Lake at the 7450 ft level and on PIcKeen Rids, Lakeview Valley *- itself has undergone substantial glacial sculphrkg. The range of landforms . section. 0 Landf oms . Landforms in the-study area are almost exclusively,of Pleistocene 4 .& < - z 42. . -- A- - s- -3 \ -- origin and reflect- the former conditions -%&erkw - Valley itself is a heavily glaciated hanging valley, tributary to the Ashnola- Valley, ranging in elevation from 2850 ta 8606 ft. The local relief in -2 F: -z- the upper part of the.va3ley is in the order of 2000 ft. The eastern ' ,. ,. - side of the valley is"bist&yished by the ab3ence of 2 indentations or A pr~jectingridges, The upper third "o the west sid* of the v llqy is potable /P .+, a. 24 %, -> .- C for a series of seven c-irqes, cut into the granitic bedrock, phe first -- A .> - four of these cirques areaccupied by tarnlakes, and t%e soutCerdost three ,- are filled wit11 debris of various~types. Two smaller lakes located on the ' -4, valley floor to the east of Glacier Lake are shallow bodies formed behind I 4. the irregular morainal material that covers the valey floor, A * "- - Lesser landforms in the field-area include tors, patterned ground, - columnar basalts, talus-cones, felsenrneer and an alpine lake. From ..+a 4 ,. *. Ladyslipper Lake into the upper cirque one moves- frdim a delta on td a transitional slope of resorted (f luvially) talus kteridl, And on to talus - C 1 cones that rim the entire cirque. Slopes increase from the lake'to - 0 0 20k730 on'ihe delta, 19'-23' on the resorted material and 36 -41 on the " -1 actual talus. Ladyslipper cirque has a lower basin now occupied by a lake p 2- , at 7280 ft and an upper basin at 8000 feet. The upper basin is filled with talus material and large blocks, 10-15-ft._ high, of volcanic agglomerate. , ,- .j 'The flat topped ridge between Ladyslipper Lake and Lake of-the Woods -'&,3 , ' has patterncd ground on its top and sides. The rudimentary sorted stone & polygons oV&Ee ridge top-occur on andesite lava 'and are 60 inches in I *- t. - - diameter. Fines are concentratcd.in the center,and fragment sizk of the .- - , rock -increases with depth. Silty material was present at a depth of & 10 inches. The polygons give way to stone stripes as the slope angle L increases. This patterned ground occurs approximately 100 ft ab~vethe t 4 -- tree 1ine. 8on-stoney areas have alpirggvegeTation on T.k?iianZ rnKsPp- - - "PO commonly have a lichea cover. Similar stone stripes,occur on McKeen Ridge f 1 -rs . > on the Princeton lava. ~$estrip& gfade into a felsenmeer of broken basalt 'b . %* ax* r" as one moves toward Py?rSdd ~ountalm. ~heseTeatures had their origin ' "-. + - during tfy! periglacial conditions Gcompanying the Fraser glaciation. .$his patterned ground is preeen-t above the inferred upper extent of the Fraser - 3 ice sheet, and in view of the strong frost action occurring under tod&s -.r -.r climate,may continue to be slowly developing under current conditions. , Solifluction lo-bes occur on side slopes of the ridge immediately north of Lildysl$pPer kke. They are usually lobes 3-12 ft across and elongated with the long axis down slope. The iobes are covered with alpine vegetation and are probably inactive or only skpwly moving under present conditions. - . A": - On McKeen Ridge periglacial landforms including a basalt felsenmeer -i and stone stripes occur on the Princeton lava. With the exception of the \ columnar basalts at DE 's Woodpile, all land forms north of the study area show the effect of stpong periglacial fiost *action. In the sthdy area, as . one moves over the Cathedral quartz monzonite-Princeton basalt contact, -. - evidence of frost action abruptly disappears and is replaced by a tor L.,J->. * landscape. The change cannot be ascribed simply'to'a lithologic difference - as70ttcrops of the quartz monzonite in areas not on this part of .*~c~bgn - -? Ridge show the effects of periglacial attack. Tors .r Tors in Cathedral Park occur only on McKeen Ridge in arcas of quartz - .* & monzonite bedrock. The tors are restricted to the portion oY the ridge d lying between the-quartz nonzinite-Princeton group contact west of Ladyslipper Lake and the topogqaphic saddle associated with a small unnamed cirque .&* .r 1 112 miles southeast of Ladyslipper Lake, AL the northern bD-w- are currently being exhumed as members of the Princeton group are stripped ' away by erosion (see photograph 3) .~The southern bokdary is less dist'ikt U occurring where the ridge suddenly narrows. The narrowing was the result &of cirque formation and expansion on both sides of the ridge during the - ~leisfoctnein this area. On the east the tor area is abruptly tr'uncated as one moves from the summit area of the ridge on to the cirque walls _ - - _ (see photograph 4). This abrupt slope change in some areas. forms vertical ' cliffs over 700 ft high. In all areas there is a minimum 1000 ft dr&p over the quarter-mile distance from the ridge to the valley floor. On the western slope tors exfend approximately to the 7800 ft l'evel in throe groups of massive, tor-studded outcrops. FrBm this level the bedrock slopes sharply down to the 7500 ft level, below which little bedrock is exposed. P- This pronounced slope break is also present near Mt. McKeen at the southern a -, boundary of the tors where the ridge drops in a near vertical cliff from 8600 to 7500 feet. The 7500-7800 ft interval is the trim line of Pleistocene valiey in the Wall Creek basin. The termination of &. the tors on this slope is coincident with the upper limit of effective -.-, *+&+. Q glacial erosion in the valley duri@g the incipient and waning stages of ice sheet development in the southern interior. The current distribution of the tors has, therefore, b& determined on the south, east, and west by Pleistocene ice acfion. The geologic contact with the Princeton group at ' ------the northern end of the tor area reflects asubstantially older control. Tors located on the south rim of Ladyslipper Lake are scparateii from the , tor area on McKeen Ridge by B narrow band of Nicola lava. This distribution, I therefore, reflects irregalarity in the--- upper surface of the pluton, a furtlicr geologic control (see figures 5 and 61.. Photograph 3.-Photograph shows tors which are currently being exhumed at the Princeton Group/quartz monzonite contact west of Ladyslipper Lake. The photograph was taken from the quartz monzonite and looks to the north along McKeen Ridge. Photograph &.-This photograph shows the abrupt trunca- tion of the tor area at the cirque wall near Smoky the Bear, south of Ladyslipper Lake. 2.5 inches cquols I mile. Tor area Figure 5.-Location of tor -areaon McKeen Ridge Figure 6b.-Vertical air photo coverage of the tor area (~ritish Columbia air photo- graphs BC 7010-139 and B.C. 7010-200) and geology of the study area. Pv-Princeton volcanic Ps-Princeton sediment L-Lakeview granodiorite C-Cathedral 'quartz monzonite N-Nicola andesite ' Th_e tork can be divided into three ca_tegoriesL including. single (isolated) tors, ridge tors and tor-studded bedrock masses (see photographs ? - 5" > .5, 6, 7, and28). The tors are in each case morphologically similar. The 2 " - 2 ' a categories depict the type of bedrock exposure present in the different areas. Simgle (.isolhted) tors are continuously present along the summit .p' %= 'area bf McKeen Ridge and rim the cirque walls oh the eastern side of the ST' ridge.. The tors of this group are physically separated from one another by - - a .gr& areas in-which IIO bpdroclc is exposed. Included within this category .- are the tors currently being exhumed west of Ladyslipper Lake and the tors prese,nt op the spur ridge south of Ladyslipper Laker The occurrence of ,. single tors is restricted to the gentl~~andmoderately sloping areas along the crest of McKeen Ridge. Moving dotmslope into the Wall Creek Valley at the north end of the tor area this zone of intact, single tors is replaced by an area of rock plinths and grGs on the steeper side slopes. Occasional - I i - - detached tor blocks are found in this area. This featureless area is - 100-200 yards in length apd ends in several massive tor-studded outcrops 'i - shortly after the 8200 fg'level (see figures 5 and'6, and photograph 7). i These massive bedrock outcrops stand up to 100;ft above the general slope IC C I / and &xtend down to the 7800 ft level, where they are abruptly truncated. f , The abrupt termination of the tor-studded* outcrops is regarded - as having 4 resulted from valley glaciar- eros'ion in Wall Creek Valley. Massive outcrops r and a similar sequence of single tors, rock plinths and grfis, and massive outcrops are also present on side slopes at the soutlGrni.SiiT cf thg tor a= %-% , I The sequence of single tors, grGs and rock plinths, and massive tor .outcrops is absent from the mAi%dleparts of the tor area,, Ridge tors are /, present in the area between Smoky the Bear (this is a pro•’ile in the rock of the vertical cirque wall regarded as resembling Smoky the ear) and Photograph 5.-Single tor on west side of McKeen Ridge. Photograph 6.-Single tors on the summit of McKeen Ridge. Photograph 7.-Massive tor cm McKeen Ridge. Photograph 8.-Ridge tor on McKeen Ridge. Giant's Cleft dame (see figures 5 anddl. Threedistinrt-,linpar*-- - ' extend down&.$e from the summit of &~eenRidge to the 7800 ft level. The . z 4 ridge tors are fhe surface features of these bedrock ridges and extend in ' a continuous line down the side slope (see photograph 8). Areas between b P the ridges are narrow avalanche and debris ehutes. Between these ridge tors "- - and the massive tor outcrops at the north end of the study area is a rock plinth and grgs- zone which extends without interruption from neat Che %* ridge sumit to the floor of Wall Creek Valley, Large talus bloiks are * present at the foot of this slope and beiow other slopes of the to$. area. , '7 '7 All tors in the area are morphologically similar. They consist of a ,. > single or several adjacent bedrock blocks, usually with superincumbent ==+ -. blocks (see &otographs 5 and 6). The tors have a distinctly rectangular config&atiun as th'eir margins cdincide with vertical joint pianes in the . quartz monzinite, The tors range from 5 to 30 ft in height. Lateral B %+ dimensions range from 10 to 30 feet. Both the bedrock an$ superincumbent *, >: ?. Y .'a 'blocks are delineated by regula~lhorizonta1"andvertical planes. The vertical 'plznes strike in directions parallel to the major vertical joint linarneqts in the quartz monzonite and mark the areas of former joint planes * in the rock. Horizontal planes are also joint surfaces. These joint defined blocks have been boulherieed, i.e., they have been differentially rounded at the coyers so that they have a subrounded or occasionally -- ellipsoid form. Joint planes have been differentially weathered and etched --- - - to depths up to 3 feet. No angular-faces were present on any tors, ,- Although the bedrock is light gray in color, the tors are dark gray when viewed from a distance due to the growth of the-black lj~heqEphebe ri- lanta on their surface. On close examinahion the tors often have a dull reddish coJor due to the superficial recementa- of the outer surface by iron-oxides. This induration protects theyinterior of the tor which in -- C- , , ', -. Tfome cases has been altered by weat%&ing agents to such an extent that it -4 ,, .\r is easily disaggregated by hand. Decomposed quartz monzonite is found over I the entire ridge and is the 'source of the gr&. More than one indurated shell may be present. In some cases the outermost shell has separated or 4. - .'+ can beceasily pulled from the tor surface. These indurated crusts formed r concentrically about the surface of the tor. - - - An interesting minor landform present on many tors were round, ellip- tical or irregularly shaped bas ins corresponding to the tlgnammatl, "panholestl , and itweathering pits" of other studies ranging in size from 6 inches to / 4 ft across and up to 18 inches deep (s$e photograph 9). These flat- / I - $$, *- ' bottomed depressions often had overhanging rims, No induration was present on the bottom or -Side's. Occasionally present were slots cut info the rock which extended partway to the floor of the basins, These depressior$ were . * in all but two areas. Tors near the quartz rpnzonite-Princeton '. group contact had no basins developed in their uppet surfaces and were only superficially indurated. No basins were found on rock plinths on the spur leading off of the main r.idge south of Ladyslipper Lake,or on plinths in % /-- the rock plinth and griis areas c6 the west side of the tor area. Many spheroidal boulders &re found on the5ridge. In one instanc; a * spheroidal boulder was observed'*which had four, concentric indurated shells e approximately 1 inch thick (see photograph 10) 1 A hemispherical rock shell - -- was found whir3 was also slightly insurated. A fiad ofpaFtX5m r5E *&& \ boulders was encountered while cfimbh-rg &I to the main -ridge fronrthe spur - - . -: south of Ladyslipper ~ake.; The outer surfaces of these boulders were , , indurated. 8 pe landscape in the study area consists of tors separated by /' Photograph 9.-Corestone with concentric indurated layers on summit area of McKeen Ridge. Photograph 10.-Weathering pits on the top of a tor on the spur ridge south of Ladyslipper Lake. -- ->------essentiarly featureless areas of gr%s. Minor landforms were found in ._ -,. * - aqsociation with rhe toys. This type of landscape has been reported from w t many widely dispersed areas 'and is the subject of a substantial literature. &?. - . @% The following section will critkally review and analyze the pertinent - .- ",s * P literature. -1; $he f inal major sectibn of this thesis the morphogenesis of the cathedral tors will be discussed along with an appraisal of their usefulness in the efucithtiorr-of tor landscapes in general. -. *. . t;. r' i .+. 9 n1 t < L 55, \\ -- - *, -B -'.z- -'.z- 2 Literature Review ------& - ~ntroduction - - + Tors are an azonal landfarm with a worldwide distribution. Tors have - a been reported from every continent, at altitudes ranging from sea level tD- * dpine elveations, and under a spectrum of climatic condy@%ons which include - / tropical, mid-latitude temperate, desertJ,-and Despite the. frequent occurrence of tors there is no 1i;erature concensus as7to what the- ' - -- - pppp - -- - essential characteristics of a tor are, i.e., what constitutes a tor land- form. Features initially identified as tors on the basis of their gross morphology have, under closer scrutiny, been shown to be of diverse origins and to have markedly different morphological details: ~ / The application of a single term to a variety of landforms is not an i uncommon occurrence in geomorphological studies. The development and usage 3. of a limited geomorphological vocabulary has its origin in twenti6th century - attempts to develop a comprehensive geomorphic model (particu'larly by ' " + W.M. Davis and M._Penck), followed by uncritical description and interpre- tation of diverse landforms in terms of those models, This often resulted in confusion, ill-advised comparison and spurious generalizations. -@ *T An excellent example-. can be-found in the usage of ghe word Htorll, Linton (1955) attempted to give the work a genetic definition pro i'osing tors to be the result of a two-st-age morphogenesis consisting of formation by . - ' dif feren-1 chemiCa.1 weathering of bedrock in a subsurface enviionment followed by exhumation and exposure at the surfame as-acce~e forms. The work "tor" had not been used with this connotation in the antecedent litcragure and all tor landforms canj-iot be attributed t,o the genesis proposed by Linton. His redefinition of "tortt naturally- prechpitated immediate, objection in the literature. ~Kmer(1956) demonstrated that a '- tor group in Yorkshire, England, had beemproduced by slope adjustment " t '. foliowing the rejuvenation of a stream, and ~iti~atrick(1958) cited cases of tors evolving Gnder periglacial conditibns. Pullan (1959) examined previous usage of the word-and attendent theories regarding their origin and ' concluding the genetic definition of the word to be unjustified, redefined - - i.t as follows: e + A tor is an exposure of rock in situ, upitanding on a11 sides form - the surrounding slopes and it is formed by the d%fferential weLtharing of a rock bed and removal of the ebris by mass move- ment3~ullan1959 pg 54). A0 ..*r I.t is this definition (without the restriction of the agency responsible for a the removal of debris to mass movement) which is impxcit in the literature usage of the word "tortt. The definition fails in that it includes neither mention of form, structure or process.--- Use of this or a similar definition 8 _: r i <- in&is;;irni&ts'-application Y has resulted in the of the term' to upstanding * . residual outcrops of variable scale and morphology and has re'sulted in an 4 = absence oi precise meaning in the literature usagk of ,~eword "tor"., .. ,. While the dtf inition proposed by Linton (19.55) is unacceptable because.@ of its genetic connotation, the definition proposeF,$ by -Pullan (1959) is poor. because of its ambiguity, allowirtg it to be applied t8too great a variety of features. In this paper "tortt and other words in the deep weathering , vocabulary will be used as defined in the following paragraph. The dcf3nktions given reflect this writer's belief that a useful bistinction can .. .be nade between tor,types on the basis of gross morphology. Many definitions +. have been adopted from those "ked by Thomas (1965). To avoid ambiguity 9 quarifying adjectives in some instances have been placed before the noun. -a?- -- - - Q 4 Although ft will appear in a later section that certain- -terms' -- wily be ------+- i * characteristically associated wi$h-patticular morphogenetic theories, no , genetic ~~~~~~~~~~~~is intended in the definition. a tor is a group of partially or"c6-ppletely boulderized bedrock blocks which are recumbent upon one another in an order;? fashion, the lower most member being rooted in bedrock; or + alterkati~e>~,a Fingl&*rounded block without superincumbent material which is-rooted in bedrock. an angular tor is a bedrock outcrop of marked angular fo~m, usually seen as a single bedrock block but occasionally con- sisting ;•’ angular bedrock blocks recumbent on one another. a corestone-is 'an ellipsoidal or spheroiCboulder entirely detached from bedrock &ich ts not related in an orderly fashion to a tor or an angular tor. Corestoncs may 6ccur at he surface - or be buried within regolith materials. 3 clitter are boulders of angular form not rooted in bedrock or related in an orderly way to a tog or angular tor. Clitter . is,normally found at or near the surface. bornhardts are dome shaped hills which stand clearly ibbb;& the surrounding terrain, an abrupt junction occurring as one leaves the general surface and moves on to the steep sides of the bornhardt . domical inselbergs are dome shaped hills which stand clearly abovk, a the surrounding surface but which lack the abrupt marginal transition characteristic of bornhardts. =- ruwares-are flattish or gently domed featuresewhic$rbarely .break the profile of the surrouh&ng surface and which may be distinguished from a pkdiment by their restricted areal extent. castle kopjes are jointed bedrock,landforms ofben displaying a castellated profile and whi,ch may be distinguished from a tor by their greater size, disorder'and mixture .of angular and rbunded forlms. ~ngularkopjes will lack kunded forms. weathering residuals include tors, domes, bornhardts , ruwares , castle kopi-- es, . coresto~esand inselbergs- attributable to a subsurface morphogenesis bk chemical weathering. ' \ 9 Tor and Inselbe~gtheories ., < <* 3 It will be made obvious in this section that-tors and various fnselberg 7 - P hrms are an excellent example of the principal of convergence which is - - emphasized in the literature by Doornkamp (19582 and Cunningham (1969)'. Convergence has been def incd as a "=ondition: ,. .. .whereby disparate processes , or dif f epee emphases of the same processes, may produce similar results at a particular stage in their operation, A basic dilemma is thus posed f~rthe geomor- phologist that discrete classifications whether by process, by -- denudation chronology, or by morphogenetic region do not-'necessarily demarcate discrete classificatians of landscape features . p (cunningham 1969 pg 58). fi: , ? Comparison of the gross morphology of many forms is sufficient to estqblish the fact of convergence, An example is the interesting inventory and series .. of generalizations perta'ning to inselbergs of all types prepared :gy%. / Kessel (1973). Kessef proposes that further study be directed toward com- parative morphometric analysis of the landforms,and that this will yield Q: valuable insight into the nature of landforms. An alternative approach would center on the role and erosional processes in the evolution of convergent landscapes. Following this second approach, this section of the thesis will be devoted to outlining and y assessing the major theories proposed for the morphogencsis of tors and inselbergs. .ft will be followed by an examination of the role of process , * 'C in the two stage morphogenesis. - Four categories have been developed into which the various theories- proposed in the literature for the genesis of the landforms may be placed, ?.. k The categories include two-stage morp,hogenesis, one-stagek%ubaerial m genesis, occurrence as erosional residuals, ,?rid structural theories, Two-stage or multicyclic morphogenes'is The classic statement on the subject of tors is the investigation of the granite tors of Dartmoor, England, by D.L, Linton (1955). The signi- &3 ficance of the article lies not so much in the originality of the topic-or'a proposed morphogenesis of the Landform, but in the fact that the article J? persuasively brought the subject of torssand subsurface weathering to the k 4 attention of geomorphologists around the world, marking the beginning of a , . svbstan-tial investkgation and literature on tors, deep weathering_and / a" inselberg iandforms. Historical accounts of the literature are conta* in *.. Palmer andJladley (l96l), Palm& and Neilson (1962) and Thomas (1974). In the post World War I1 literature, the theory proposed by into: (that tors have a subsurface origin under warm qnd wet interglacial or Tertiary con- ditions) was anticipated by Handley s work (19%)- on the origin of tors in Tanzania and the work by New Zealand geomorphologists on schist tors which occur in various stages of kxhurnation (J.D. Raeside 1949, F.J..Turner 1952, -, W.T. Ward 1952). ~i&on(1955) regarded the Dartmoor tors to have formed by a two-stage rnorphogenes is stathg: h Tors, corestones and possibly other residual rock forns, are the result of a two-stage process, the earlier stage being a period of ' A extensive subsurface rock rotting whose pattern is controlled by . structural considerations, and the latter being 9 pe>iod of exhum- ation by the removal of the fine-grained products of rock decay * (Linton 1955 pg 472). ._ . . A tor is a residual mass of bedrock produced below the surface level by a phase of profound rock rotting effected by groundwater and guided by joint systems, followed by a phase of mechanical stripping of the incoherent products of chemical action i in ton 1955 pg 476). 4 The tors were produced by differential chemical decomposition beneath B *+ . an incoherent regolith consisting of the residual materials of earlier 3 weathering. Due to the negligible porosity of the granite bedrock, the attack was directed along joint planes in th.e rock,with the spacing of - - vertical jointing assuming the dominant role in determining the intensity .,- .,- - of the attack. Spatial variztion in jointing results in irregular decom- position of the bedrock, with massively-jointed ar-eas undergoing slow attack while closely-jointed voluies undergo a more rapid and deeper decomposition. 'P The chemical attack progressively rounds joint-bounded blocks into spherical; or ellipsoid forms, he stripping of theregolith and exposure-- of- the- - - I I bedrock topography is regarded by Linton as being'due to climatic change,_ + occurring under periglacial conditions in the Pleistocene. Tors would ?$: ?$: occurlin areas- where subsurface decomposition was limited by massive jointing, 4 while more closely-jointed areas would be characterized by an absence of positive relief. The interpretation of tors in temperate areas as rel'ct\ * landforms constitutes Lintonts major contribution to the understanding of - tor landscapes. . ., - $ C.D. Ollier (1959, 5960) followed a similar evolution sequen5e. on a much larger scale in his analysis of the it-rselbergs of Uganda, expanding,an 8 ' the work of Pallister (13561, The incipient landscape, according to Ollier, , was a bedrock erosional surface (~ondwanasurface) which underwent a period of extensive chemical weathering and limited surface erosion k uring the Tertiary,'resulting in a two-story landscape'consisting of a basement bedrock , surface and an erosional surface. The deep weathering penetration was irregular due to variations of rock type, texture and joint density, A period of accelerated erosion caused by uplift of the area resultedtin the down cutting of rivers, which became located in zone3 where the weathering penetration was greatest as they adjusted to the underfylrig structure. The ' , , higher portions of the weathering front occurred beneath the interfluves on which the Oondwana surface was preserved. Valley widening %y par2llel retreat of slopes resulted in pedimentation producing a new, low relief < - t - surface. Eventually the Gondwana surface was completely eliminated, exposing 7 - bedrock cores of.the former interfluves as inselbergs. J.A. Mabbutt (1961) also accepts a two-stage niorphogenesis for domes and tors in AusCraliz. He proposed that the domes and tors were isolated in . the subsur>faceby deep weathering under humid climatic conditions. The * ,-." 4- -- - - -&I,-- - I t-i ------Eompartmentalization of the subsurface landscape was due to" structural .., (principally joint) controls, A lateritic crust formed on the upper pene- plain surface. The peneplain was subsequently dissected foli, owing uplift \ .- of the area. Exposure of the bedrock landforms was not due tv valley \ - widening (0llier 1960), but r&wlted from a climatic shift 'to akid conditions, \ >.2 , .. Under the changed geomorphic regime the bedrock was exposed, as \$he duricrust vr -.,y \ \ \ - capped escarpment mrcferwent stow retreat and the regolith wassbipp~daway. M.F.,. Thomas (1965) regards the bornhardt landscapes of ,/ product of differential subsurface weathering and surface erosion. His idealized cycle begins with substantial deep weathering beneath an uplifted senile landscape. The irregularity of the bedrock surface is a function of * variable'joint d'ensity, but the isolation of massive residuals in the \ -subsurface itself results in the subsurface development of extension; jointing \ creating domic&l forms. Rapid exhumation occurs following rejuvenati4n of I - i drainage if a closely spaced stream network is present, Otherwise, emergence t of the bornhardt landforms is delayed until*exposure by the presumed parallel retreat of valley slopes. Exposure is a function of* the relative rates of \ surface stripping and basal weathering. Both agencies are synchronous and ' the relative effectiveness of the opposing forces will be =efle;ted,in-the depth of the regolith and degree to which the weathering front .is exposed , at the surface. Expos'ed bornhardts are largely,irnrnune to subaerial weathering 5, attack, gro+wing downwards by continued subsurface decay and attaining ------.------.L. - greater heights as erosion exposes more f the mass above the topographic - - - surface. Final destruction under subaer a1 conditions is due to the opening of latent vertical jointing, causincJ7 collapse into a castle kopje and reduction to a ruware. Ruwares may either mark, incipient or disappearing , bornhardts. Bornhardts are multicyclic landforms and do not necessarily- reflect distinct periods of weathering and erpsion.- 4, ' F.F. Cunningham (1969) presented a morphogenetic model for theStors and bornhardts of the Laraniie Mountains, U.S .A. The tors and bornhardt2 form as products of deep weathsring with a dominant joint control. Exposure of the forms results from a change of process and/or climate sufficient to accelerate erosion while slowing subsurface weathering. The various tors band barnhardts are exposed and evolve under distinct periods of peneplanation - -- 2 -- - A . . - - '- and uplift. Forms are regarded as undergoing substantial subaerial evolution during successive denudation sequences under changing climates. i Some of the distribution of the forms is doubtless due to structural con- siderations -fi;sized gY Eggler et a1 (1969), but the:morphology~and :2 ,-.-. . evolution of the forms under changing geomorphic conditions cannot be under- % stood on a structural basis. T.O. Oberlander (1972) rejects the traditional subaerial arid morpho- ii genesis of the granitic terrain of the Mojave Desert. The domed inselbergs are the undecomposed'cores of Tertiary hills from which a weathered regolith has been stripped,, The domical form of the inselbergs apparently reflects the configuration of the original hills, i.e., production of the original hills by fluvial action must have been followedby opening of domical joint'ing parallel to the hill surface. The isolation of the hills is ascribed to Tertiary fluvial action rather than variation in the bedrock joiv density. The- boulder debris which cover soke'domes is identical to Regoliths are preserved beneath -lava flows L- dated radiometrically as Pliocene. The contemporary landscape formed under . semi-arid conditions in the Tertiary,and increased aridity in recent times is exposing and slowly destroying the Tertiary forms. The theory was anticipated in Mabbutt (1966) ia his discussion of +dimentation in I a. ------T .Australia. Nossin (1964) has described hills in Malaya which are currently ," %" undergoing simultane~us~parallelslope retreat and penetration of the , L -s, I . weathering front into the hill, gradually reducing it* Stripping of a hill - *, of this type could conceivably produce a landform similar to the domes and 4.' 4.' boulder slopes of the Mojave Desert. P A special case of tors due to weathering and exhumation are the ; t - . dolomite tors of Derbfshire, England, investigated by Ford (1963). Iso- :' 1. lation of the tors is dbe to solution of the calcite in the dolomite, with .- I tors occurring in resistant areas, The solvent action occurs in both surface and subsurface environments. t - One-stage morphogenesis * A one-stage morphogenesis of angular tors is proposed,in areas which - have undergone periglacial conditions in Pleistocene or recent times. An early proponent of the theory was Peltier (1950) who proposed "isolated remnantsw (tors) -to be expected-features of a periglacial geomorphic cycle. Palmer and Radley (1961) and Palmer,and Nielson (1962) were principal exponents of the periglacial hypothesis,but the tors in the areas in which they worked are more probably the products of a two-stage evolution, with f Pleistocene conditions partia.11~modifying pre-existing landforms, /--- -+i r The theory is,best demonstrated in the work of Demek (1964) and tors formed in their entirety by Pleistocene frost attack, These writers ., I \ P postulate angular tors as a,product of a general scheme of periglacial slope develop~entincluding altiplanation terraces, f elsenmeer>$ solif luction and * d*.. - = escarpment retreat. The onset of periglacial conditions results in the ... removal of unconsolidated material from slopes by solifluction, exposing_------ the underlying bedrock. Differential frost shatter& of the bedrock . produces.cliff faces which are obvious zones of slope disequilibria. Under - ' >/ -*+ . continued frost attack the scarps undergo patallel *s~<~efret~reatleaving ' I altiplanation 'terraces in their wake. Vertical jointhfg, poviding access .planes for water, exerts an impoftant structural control. Multi-level , scarp retreat is csnsistent with the theory. Angular tors form as resistant - * 2. 1 masses are isolated by irregular scarp retreat or are- left as.stacks where retreatirlg escarpments intersect. Waste 4materia1.i~ left as felsenmeer, reduced by further macro andmicrogelivationto grus, or is removed by .s .s -- solif luction. Czudek (1964) emphasizes the role of lateral rather than vertical planation under periglacial conditions, contrasting the slow lowering of the altiplanation terraces with the cojljparatively rapid scarp retreat. This 4% is attributed to the role of permafr&svt.as a basal limit to frost action on the-. terraces and the more exposed microclimate and rapid frost cycling on C.f . - the cliff faces. The importance of local faczbrs in the isolation of I angular tors including microclimate, joint density, petrologic and lithologic variation, and springs are cited by Demek (1964)- Principal factors regarded * as establishing the periglacial origin of the angular tors include the absence of significant chemical alteration on joint skfaces, their angular form and close association with other periglacial phenomena. +" b. Other one- s tage morpi-tog msis tfr~ories under-perTgCaclaLrondif~Ons have been .proposed by Dah'l C '1966) and Berbysktkre f f9fZ). Dahl regards schist e -x tors in Norway to be the product of rnicrogelivation and,s5a lesser and uncertain extent, chemical weathering under periglacial conditions. . - Derbyshire proposes tors to evolve by chemical. weathering under xeric . - periglacial conditions on a nunatak ridge in Antarctica. In the latter - -d. ------cases the tors are rounded, not angular. Much evidence, however, suggests that'Derbyshirels theory must be regarded as unsubstantiated rand fund- - $mentally unsound. Discussion iS deferred to a later section on glaciation. The angularity of periglacial tor forms contrasts sharply with the ?r rounded tors produced by subsurface chemical weathering:;. - #%+The ,a. dif fe+nce is attributed to the markedly different behavior and nature of bhe attack, - - particularly the selectivity of frost action when compared with subsurf.+ .->& % weathering. A general association of tor form and genesis occurs in the literature although the association is complicated by the periglacial re- L* P' sculpturing of two-stage tors,and the structurally determined angularity of 1 9 ' ,P* .. two-stage schist tors. Again, discussion -is'deferred to '2 later section.. -%. -%. ' A final subaerial hypothesis that .must be considered is, implid=in theories which attribute the dome and boulder slope terrain of the arid American southwest to subaerial development. The spheroidal boulder6 are regarded as being formed by chemical weathering on joint' intersections, % surface wash (~avis1938) or . frost action and chemical weathering elto ton 1965). The theories lack a subaerial process capable of the *6 differential rounding of a duboid block,and have been su6erseded by the =. genesis proposed by Oberlander (1972). Fluvial erosion ?. A theory whf e4-t regards f iGvia3 processes as t-trc-prhtckpal mechanisms in the evolution G•’inselberg landscapes- has been: propsad -by L. King .'(4948, 1958, 1966). ~fritan-inselbergs."&re regarded as evolving by joint-controlled drainage incision in a low relief. Incision would be favored in heavily jointcd ." first in valley formation, . A -f= . 66. - < ------ W ' ,and then in pedimentation as parallel scarp retreat-hegin.;, ThefFnal- - -- remnants of the old peneplain are the resistant, massively-jointed areas which riserabove the lower pediplain as bornhardts 'and inselbergs. Tors evolve in the same manner, though on a reduced scale. King does not regard A deep weathering as necessary and points outthat many inselbergs stand higher than known depths of subsurface weathering. This and other objections of King to a deep weathering evolution are answered by Thomas (1966b). - - - - ,- -- - - , * b Savigear (1960) has argued that inselbergs are irregu-larly distributed, aGd i show no consistant relation to drainage or erosiona~~es&ipments, while the fact that inselbergs occur only below the Gondwana surface is suggestive of a weathering origin (0llier 1960). In areas of Uganda where deep weathering is absent due to radid drainage, incision and erosion, Doornkamp (1968) notes inselbergs do not occur. v . A strict application of King's hypothesis is accepted for sedimentary ' domes in Australia (01lier and Tuddenham 19611, while ;he theory in con- junction with deep weathering has been accepted by Hilton (1966) _in Ghana, - Eden (1971) in Guyana, and Ojany (1969) in Kenya. In each of these cases, slope retreat is thought to occur under a deep weathering mantle, not under subaerial condi,tions. Structurally-controlled river incision and velley widening are a>cepted by Ollier (1960) and Thomas (1965) 'as a means of dissecting a deeply weathered landscape. As it is apparent that slope -- t4 retreat may be responsible for the exhumation of subsurface features, an 1' emphasis on one process or the other will lead to app$rently different /' ., origins for the same features. ., A convincing case for the origin of inselbergs of the Virginia and North and South Carolina piedmonts by drainage incision and slope retreat is proposed by Kessel (1974). "The inselbergs are grouped into four classes ff. c' c' ", , 67. ------ C including dissected mountain masses, detached- - se@ents-- - - - of linear ridges, - - outliers bf mountain escarpmpnts and complet~lyisolated inselbergs. Drainage incision divides an \uplifted surface into discrete comp&fments and 1 is followed by lateral slope i;replacemekt-(slope retreat) by mass wasting, * I I. ' surface wash, through flow an4 gullying on in iitu deep weathering regoliths: \ Slopes falling below a relief threshold or failing to maintain a sufficiently steep gradient, kbwnwaste rather than undergo slope-re- -- - - t - Structural ahd lithologic factors are ii%bortant inr the; morphology of . L individual inselbergs. These mid:Iatitude insclbergs are attributed by ? #;essel (1974) to slope retreat following hainage incision beneath a deeply LP weathered regolith. 6, " A special case for the evolution of tofs by fluvial processes has been proposed by Palmer (1956) ,in gritstone bedrock of Yorkshire, England.? Stream rejuvenation resulted in instability of tee valley-side slopes which -' . A-- began backwasting in order to achieve B,Gew stable gradient. The initial adjustment occurred on- the lower slopes; working progressively upwards. Where the downwasting encountered a resistant gritstone bed near the top u of theryalley sides, a scarp developed with slope adjustment continuing by scarp areat isolating joint bounded blocks in the grititone. Adjustment continued until the scafp was eliminated, but the isolated gritstone blocks remain 2s tors, evolving slowly in a dry microclimate. The theory is -3 -, . ,-eminently-Yeasonable but has limited application. A Structural theories :/---- m" Structural c~nsiderat~onsand influences have an important role in each of the theories mentioned, usually guiding the action of surface or subsurf ace weathering processes. ~thcturaltheories differ, only in that a,. 68. -- t -I they' attach a dominarit role to rather than empha------sizing a weathering process, Twidale ( 149, 1971) rA$gards structure, *, 1 particularly jointing and the distribution of tectonic stress in a rock 7 . +* .. mlss, as being ,of pre-eminent importance in the evolution of domical insel- h " bergs. Cunningham (1971) has proposed' that s in Idaho may be cupola forms inherited from the emplacement of a pluton, and notes that ,the interaction between magma and c~unf;~rock mag assume a dominant role in --- the geomorphic e~olytionof the area, particularly as ,the plu'ton roof $s , 8 - first exhumed. ~hegetheories are suppdrted by the work of ~olborth(1962) ii Nevada whq found both granite cupolas having tor-like fohns and readily weathereg ltrapakivi-granitet'in the roof areas of partially expo&ed granitic plutons,and placed their development at the time of emplacement. 8 Cunningham's proposals (1971) may have a wide application in the explanation 3 - of tor and bornhardt landforms, P1 Pi All of the theories which have been described present reasonable models for the evolution of some domes, tors and inselbergs. In many cases the . I genesis is ascribed to the major process thought responsible for the form while acknovledging a lesser inf luence of other factors. ~ors'-wd insel- ? bergs are outstanding examples of the principle of convergence. Although "d gross morphological characteristics are similar in many cases, the more ' detailed examinations of form reveal a remarkable diversity., In the case of weathering residuals Ruxton an&.~err~(1961 pg 290) observe "the variety of landforks that may be exhumed from a &hick regoli& is considet.ab~'. * ~deremainder of this secrion will be devoted to a discussion of various m -b topics in the two stage morphogenesis of tors and other weathering residuals. --- .prZw .>-- Weathering is a ..sp~ntaneo~s and essentially irreversible interaGtion S $ - rocks with a surface or near surface environment and includes both * physical and chemical processes which act td reduce .a rock from its original - 4 . '.* form and statg, Chemical weathering has been defined by Loughnan as: * .. .a7 process by which atmospheric, hydr~spheri~q,and biologic agenciesjact upon and react with the mineral constituents of rocks within the zone of influence of the atm~sphere,producing> relatively stable, new mineral-- phases (Lougkn-an 1969 pg 2). ------ The principal processes include .oxidation, . hydration, base exchange, 1. d chelation, solution and -hydrolysis. The'se normally act in conjuncthn with one another such that actual weathering reactions cannot be attributed to t a single process. Secondary-mi:@eials are formed as soluble components of - thZ original minerals areyremoved, and water, hydrosyl groups, oxygen, carbon dioxide, or dissolved materials from the, boundwater, ,dr Btmosphere ,, .-' ,are added, Chemical weathering proceeds by exothermic reactions subject " a I to the laws-: of chemical equilibria, and plausible reaction formulas can be ' developed which depict idealXzed reactions and reaction sequences. ~ltkough useful for purposes of exposition, they ref l&ct poorly $he complexity and , z , ' I variability of field weathering conditions: Chemical weathering may completely decompose a rock unit,or-by selective' and limited alt&ration I cause its mechanical disaggregation. Excellent treatments, of the topic are contained in Goldich (l938), Rieche (19451, Keller (19571, Kra~sko~f'(1967) ) and hughnan (1969). - --A - - Chemical weathering proc&ses acting in the subsurface assume a dominant role in the morphogenesis of weathering residuals in the presumed - ++- ', two-stage morphogenesis of tors, The bedrock is d'ifferentially altered-such that intact rock passes are left between and beneath an incoherent regolitha - - - 70.-- - - - --- 3- -3 consisting of secondary minerals, corestones and other residual bedroflc '-h materials. Erosional processes are intei-preted as passively exposing a , . portion or all of this bedrock -s$rfnce. The s;buerial morphology of the a P. features is inherited f r&< the former subsurf ace environment, and subaerial ~eathering~attackgenerally produces no substantive change in the features, but issrcsponsible for disbinctive minor afterations. The enormous .signi- I 3 h. ficance of the subsurface chemical attack demands a discussion of the B B . I . .. *. relationship between process and form. ,% .- - c 6 - ** The factor chemical weathering processes is their .a fl inextricable dependence upon the '{reience of water (with the majol$~xcepfion * ** , ... ,' 'I r of atmospheric oxidation). Watera-is a% once one of the major reactants, a sol in which other reactions take place, and the agency 062 4 both decornposini agents and soluble reaction products. ,The l&ter % I characteristic insures that-.= weathering reactions will not be terminated by ' the establishment' of a chemical equiiibl9ium. These---- chemikal keactions-are impfbmented by meteoric- ra.aters moving ve;tically and raterally through the .> , bedrock and overlying regolith. 4 Y- The low porssity and permekility of crystalline rocks (see ~essfi; 0, . - .= )b- . LZ? ,, . ' et a1 1940) -indicate that Lm underlying crystalline bedrock will constitute I'? <. an effectively imperneab~e_surface,marking the/ lowest penetration of 'j . A meteoric waters. In the absence of vertic?l planes down which water could . . Oa penetrate, chemical- vcatheri& attack would be%ecessarily 1 a ' &? $- sing16 surface. ~ointingland, in particular, vertical jointing ,will accel- - f 7 1 5 eratc the-weathering of the bedrock by allowing it to proceed in three, & ' rather than one dizcnsion. The- limit of weathering penet&ti&' has been' *.. r % . .. -8 ,e--I - &.-.%&-. e~alLed the "basal platform1' i in ton A9551 and the "basal su;facefl*- t 4- c (Ruxton and Berry 1959). Mabbutt ( 1960) propo~edt$ term "weathering front" because it was, both dmieand non-direetfoml. we^^ fnmt M1 -be - - A used in this paper to denote the surface marked by.-deepest penetration of chemical weathering processes into bedrock. In most instances the weathering front will be in the subsurface, but it will be subaerial where bedrock is exposed at the surface. ." A common miscohception in the weathering residual? literature is that *, weatheryAg is limited to acid, aerobic conditiws in the ;adose zoneand would be non-existent or sharply restricted beneath the water table. Linton (1955) Pegarded weathering to b*e limited to the vadose zone And . Y writing of the water table stated: i ...below its level the restricted circulation will inhibit chemical reactions, since equilibrium concent&ions of soliible reaction'pfoducts will soon be builr up in the &earlg stagnant groundwater-(Linton 1915 pg 475). Ruxton and Berry also supported this position in stating "subsurface water; .' i" containing, or\in association with, atmospheric gases .is the prime cause of weatheringt' (~uxtonand Berry 1957 pg 12741 and the collary statement 'r thgt Itthe lowest level of the wafer table acts-as a base level in the 6 1 -, normal pro&.ses of weathering" (~uxtonand Berry 1957 pg 1275). In later investigations of tors and weathering in Australia, Mabbutt (1961) and f" t Browne (1%4) also-p'roposed the lower limit of the ? This mi-sconception arises from the presumption that the reactivity- OF groundwaters is due to the absor~tionof GO the generation _of Ithumic" - 2' r # r 2 acids in decomposing organic materia1,'and thqnssociation of wwhcring with . * I oxidizing conditions. The reactivity of groundwaters, although maximized ifi ts the vadose zone, cnnnot be rsb%rdcd as being exhausted in the phreatic zone or where the waters are no longer\ xid. 72. - - -44' + The constituent minerals of silicate rocks come into chemical equi- '9 librium with an aqueous sol at characteristic pH values which are suffi- ciently consistent such that Stevens and Cannon (1948) proposed mineral > + identification by kheir "abrasion pHtt. Minerals react spontaneously with ' \ k - arr-aqueous sol. The reactions are marked by an increase in the dissoived ion concentration and a rise-% in the pH until equil>brium values are reached. . %I While abrasion of the minerals speeds the process by increasing the surface - - - area on which reactions occur, similar reactions will take place under,natural d conditions. ~inerilsare inherently unstable in the presence of water. -9 Valuessf equilibrium pH obtained by Stevens and Cannon (1948) fo 0 common minerals ranged from pH 8-11 (quartz was pH 6.5).' Brfglord et a1 (1963) in experiments with neutral and C02 charged sol pH 5.5) found found equik hri 11; 'p~and dissolved ion concentrations.a to be reached following the abrasion of min.er+ls into the sols, but also fouid that-the concentration of specific cations and reaction intensity to vary in the two sols. The & reactions, however, were spontaneous and continued until alkaline equilibrium pH levels .were attained. ~~drol~s~sreactions, following this experimental evidence, can neither be limited to acid groundwater environments nor restrict- ed to oxidizing condi~ions. ~lthou~hoxidation will cease in the phreatic zone, reduction reactions will be substituted and be a nxmal feature of continued weathering. The oxidation state of some elements2~particularly iron) is strongly dependent on the en~ironmental-pH And Eft (see Kaplan et a1 .- -. 1966, Garrels and Christ 19651, and the expected minerar p3Ze will @Tate ' P,. to tftede factors. While chelation may be limited to near-surface enviE ments (most chelates are of organic origin), base exchange can oaur at any--level.' F P Simple solution is strongly dependent on the chcrnistry qf the groundwater sol, and both the rate of reaction and the type of cations taken into solution i will vary with environmental p~-(seeChorley 1969 pg 6U; ~ydrh-t limited by environment, Water molecules absorbed on to crystal surfaces may become polzrized to an extent that the molecule dissociates, initiating hydrolysis reactions (~enny1950). 'Phis process is largely~ v independent of environmental pH and Eh. 7 Chemical reactions andweathering are ndt limited to the vadose zone . but will also occur in the phre&tic zone. Even where equilibrium con- - - - centratiohs of solutes are present, some reactions (hydration, base ekchange) will continue. A less vigorous circulation in the phreatic zone may result in weathering stagnation, but in 'hekt cases lateral movement of groundwaters I into streanis, rivers, lakes and the ocean will ensure continued recharge of waters and rimoval of soluble weathering products. In view, oE the slow rates of weathering,even a very slow circulation and recharge would be sufficient to insure the continuancc of weathering renctions. Altl~oughit is possible w that stagnation of groundwaters in pockets of dcep weathering may limit 1 . , C downward grovth of the weathering front,.Leloong (1966 as quoted in Thomas 1974) has proposed that isothermic diffusion of ions can lead to the removal of dissolved ions from depths and their concentration near the sukface, The %.* - ., r-- . - .< 'I theory was based on well data - wbuld effectively preAyde equilibrium concentrations of dissolved fins from being attained.-in phreatic waters. 5 * Chemical vcac&ring of rack will proceed "here the rock is in conthct _- with reac_ti~$: meteoric waters. The lower limit of chemical weathering -8-"-, - will normally'be the impermeable bedrock surface in crystalline terrains. Reactiuns will be most aggressive and alteration greatest in the near surface i r' portions of a piofile,and will dccrense downmrds as th$ groundpter sol J approaches n chemical cquilibrium with the regolith material. The weathering I front has no theoretical penetration limit and. weatheringgrofiles over 74. r. - --- - I000 ft deep haGe been investigated by 0llier (1965). The actual depth of ------weathering penetration (as .oppos6d to tl-e &pth of the intact regolith) is difficult to estim,% te because of the'impassibility of determining the amount . . , of regolith removed by ero~ional~processes.In addition, actual rates of decomposition for different rock types, under different climates, and at - 2 dif fereit levels within a regolith have not been determined. Chemical ' weathering remains, however, a spontaneous interaction of rocks with meteoric waters in both phreatic and vadose zones, limited only by the s establishment of a chemical equilibria or thd depth of penetration of meteoric waters, t Spheroidal weathering IdA fundamental characteristic.of water in the subsurface is that it will f envelop all surfaces without directional bias (this assumes that water will be equally distributed and available to surfaces). A consequence of this is f that chemical weathering will be pan-directional'and attack all surfaces - equally. Assuming a h~~~geneous,isotropic rock mass, the attack will be r . , most concentrated in areas with a high surface arealvolume ratio. Pan- - directional weathering attack will' favor spherical shapes in which the specific surface is minimized, A three dimensional rectangular joint net- work is comonly presmt in crystalline rock, and if joints'are sufficiently -. ~ dilated to allov~ the pcnetratibn of groundwaters, then joint-bounded-blocks will be separated frma the bedrock ad ramded ia&-elLipwLda-1 andspherical r (I •’am, T& reality of this behavioral characteristic of subsurface chemical attack is demonstrated by the regolith profiles described in'Hong Kong by Rueton and Bcrry (1957) (scc figure 7). Profiles shoving no significcnt variation from this nodel ;lave been reported on various rock types from -, - - / Zones in a weathering profile---p-p ...... _ IV. . '0- * 111. 11, . . '1V.-Zone of struct'ureless residual materials 111.-Zone of free corestones and residual materials I1 ,-Zone of spheroidally weathered joint blocks I.-zone of initial alteration of granitic bedrock - Two-stage morphogenesis of tors 1.-Chemical weathering resulFs in 11.-Partial exhumation of the an irregular subsurface ' weathering front exposes weathering front beneath spheroidally weathered bedrock decomposed rock material at the surface as a tor - Figure 7.-The upper figurc depicts zones in a deep weathering profile (after Ruxton and Berry 19571, and the lower figure is a schc~aticpresentation of the two-stage morphogencsis theory proposed for tors (after Linton 1955) 76 . C -4 ..-B f -- - D around the world adwa wan ski and Ollier 1959, Mabbutt 1961, Fitzpatrick 1963, --- (~ossinand Levelt 1967 and Oberlander 1972). The tendency toward spheroidal - 0 weathering and a regolith profife-as dsscribed by Ruxton and err$ (1957) F,, . - .? :,- - * *. are azonal phenomena. - D The weathering profile and sphe,roidal response of joint-bounded bloclts have obvious significance in the two-stage morphogenesis of weathering :. ?- residuals. Tors are partially-rounded joint blocks, rooted in bedrock, with @ supei;/incumbent blocks which-also show spheroidal weathering. The evi&nFeL * of kunded or subroundcd blacks and corestones has come to be diagnostic of * > subsurface decomposition. Subaerial attack is characterristically selective A ,A 2- - and directional and does not inherently favor the production of spherical forms . The actual mechanism of spheroidal weathering was the subject of work by Bisdom (1967). In an investigation of the origin of spheroidal structures, :. :. . 1 he attributed them to weathering penetration along a micro-crack system ,in the rock, Four zones within the rock were distinguished. An innermost ~nweathered~zone(::here micro-cracks were pre-existing structures) was succeeded by a zone in ?lhich iron staining (indicative of alteration of biotite and hornblende) was present on micro-craclcs. Some micro-cFacks had , formed as a result of chemical weathering, although most were still inherent structures. The third zone showed a dominance'of micro-cracks due to 2'- weathering processe? and substantial chemical alteration was present. In - the outermost zone macro-cracks are present and scales arc released. ------ Weathering proceeded inwards by progressive exploitation and formation of micro-cracks, 2nd the differential growth of crads parallel to the rock I surface' resulted in concentric weathering. Micro-cracks are the source of : the permeability of granitic rocks (~essleret a1 19G01,and 0llicr (1971) +- regards them as the dominant control of incipient wea~h,erin~, An interesting feature of spheroidal weathering is the formation of, concen&ic shells on corestones. The boulder core is often uriwcathered *: while the weathering intensity increases radially outward. Often found is 3 >o&f. banding due to the presence of iron oxides (~uxtonand Berry 1957). While the simple action of subsurface wcathering explains the rounded block, ..x* , . much attention has been given toward explaining the origin of the concentric'" -bd - shell. Chapman and Greenfield (1949) concluded that the weathe ?i'ng,of basalt spheroids moved concentrically inwafd: Shells split off due to the volume increase of secondary minerals formed during weathering. Separation of the shells occurred along curved planes parallefing,the boulder surface. A simi- F' lar origin for concentric laiers was proposed by Simpson (1964) who found that the formation and expansion of vermiculite+clays resulted in-the dcvel- ; <. ' 7 opnent of concentric shells in a graywacke. . ,, c-Ollier (1969) proposed that spheroidal weathering took place without - volume alteration and that a Liesegang phenomena similar to that described % by Carl and Amstutz (1952) was responsible for the color banding. The spheroidal weathering was regarded as occurring by periodic chemical altera- tion without involving volume change. Field evidence that weathering does +? proceed without 'volmk alteration was given, including: ljpreservation of ' minor structures in the regolith, including quartz veins and xenoliths; 2) preservation of the octline of former joint blocks; 3) thepscurrenc?of weathexing at, depths at .:;ttFth arol~~xpzms~o~ishp&abIe- due She high confining pressure of thc overlying regolith, Most writers, houevm, rciard L* spheroidal we>-thering 2s being accompanied by volume increase. Inadequate data are available to assess the extent tk which vol&c change occurs in spheroid- al wcnthering, although nuch evidence suggests it is a common occur.rence. a .- - Ig sperimental work Carl and Amstutz (1958) succeeded i~ simulating * 2. ------Liesegang rings in an artificial sandstone,and proposed that the banding was d s-' the result of periodic chemical precipitation. the banding common in ~ani- - tic rocks is due to ir6n minerals (oxides), and the authors questioned whether ', the iron itself was migrating or another substance was diffusing, causing a , . I periodic pll change and deposition of iron minerals. The existence of a Liesegang"~~henomcna3 8- in actual rock was confirmed by Augustithis and Otteman (1966) who discerned two opposing elemental migrations which produced-alter- , & a*- nating 'zones of enrichment and depletion of certain elements in the rock. The opposing migrations were of calcium,'and of aluminum, silicon, potassium, zirconitm,' yttrion, and rubidium. Iron in the rock was mobilized and pre- - . ." cipitated in the calcium zone, possibly because of p-H conditions associated with the calciw, znlgration. Bisdom (1966) postulated that this migration 2 ' < would occur along micro-crack systems in the rock. 5 Other explanations -of concentric shells include the release of radia'l ,L stress latent in the rock armin in 1937, Oen 196.51, the influence of concen- tric crystallization about core/ areas in a magma (~chattner1961, Demek 1954b), radial mineral layering and tectonic movements (Twidale 1971), an$ C ' the influence and action of hydrothermal solutions'(Pa1mer and Nielson 1962, Ford 1967). These theories have not been conclusively demonstrated and P cannot explain the common case of concentric shells around corestone3 as ,they evoke special' conditions. Eon-meteoric alteration The chemical alteration of rock may be accomplished by agcncics other . than meteoric waters 2nd associated weathering processes. The source of i non-meteoric alteration is generally linked to conditions resulw from thep ------the emplacement and cooling of magma, Alteration due to these conditions . ,+ ------may be confused with, or id-Tstinguishable from meteorfc weathering, resulting ,+. in an incorrect evaluation of the origin of the associated landforms. The alteration i,~generally efftcted y a combination of heat and solutions rich >' ic: 2 in water. and other volatiles,and is frequently termed hydrothcrmal alteratim. . , I A hydrotherma1,source has been proposed as the origin of maby ore 0 bodies and it is from this source that most of the information about hydro^, \ - - - % thermal ueathering has been derived. Most silicate minerals are anhydrous, C resulting in an increasing water content in the magma as crystallrization proceeds, The resultant hydrothermal solution may be accompanied by a gas .I phase,and is accepted as a normal stage in the crystallization of a magma. Should the solution penetrate :the country- rock, dist-inctive at teration and minerelization in this body ~~ouldoccur. If it remains within the magma it . .r" reacts with previously crystallized material in a later, deuteric phase. Other sources of,the waters of hydrpthermal solutions are primeval- waters trapped in sedimentary rocks,and cir'culating groundwaters which become heated by proximity,with an incompletely cooled magma (such solutions may be visible at the surface as hot springs, fumeroles and geysers). Products of hydro- thermal origin include mineral veins, ore deposits or a more pervasive alter- ation of the host rock to minerals stable in the presence of aqueous solu- tions and elevated temperatures. In particular this alteration may involve , r r 5. : th'e formation of clej- minerals which arc impossible to distinguish fro* those produc-ed by netc~rirweathering C~he-s~zu~~ured-tkeminezdsare 4 identical to those formed by meteoric weathering* oply the mode of origin is different). Factors conmon1-j regarded 2s establishing the presence of hydrothermal alteration include .the presence of mineral veills and ore 80. 2.- - * . " ------ / presence of the clay minerals nacrite and dickite (neither of which has ever e been recorded as a weathering product, see Loughnan 1969), the non-con- d 4 formity of a clay mineral deposit with the clay mineral types dominant in Bn area (~acobs-and- Kerr 1965 found kao18in in an area dominated by illite S 'and montmorillonite and used this factay, along with other supporting r -. evidence, to establish the hydrothermal origin of the kaolinj, the presence . . 1' of anomalously pure clay deposits den andwreen 1971 distinguish between e 5 - - - griis and hydrothermal kaolin deposits en'. the basis of grain size and / mineralogical analysis), and the presence of incoherent rock beneath d sound rock (Cunqingham 1971). Evidence of hydrothermal alteration has a limited occurrence in the ' P deep we5thering literature. The-controversy over the origin of the Dartmoor tom da in ton 1955, Palmer and Nielson 1962) was due in part to a disagreerhent over the origin of the griis and kaolin deposits. Def-inite hydrothermal 0 kaolinization and other nineral'izationare present in the area (palmer and Nielson 1962, Exley 1958). Eden and Green (1972) have demonstrated z - that in fhis case the grcs can be distinguished from hydrothermal clays apd is due to-meteoric weathering. ~ord'(1967)fohd evidence of 'bothdhydro- 4 thermal and-deep weathering alteration. w he hydrothemal alteration is not described mineralogically but is Gsigned a pre-Triassic age. Deep ' weathering is limited to igneous rocks which rise through an impermeable @. . Triassic mantle and is in mqy cases associated with hydrothermally altered -4 . .dC zones. The to which each was responsiblB.u n the deep weathering . 1 was not established. Cunningham (1969, 1971) has cited evidmce'of hydro- - thermal alteration in tor hnd bornhardt landscapes he investigAted, and Cainc (1967) r'egarded at least some tors to be due to hydrothermal altcg- * # ation. A regolith cited by Thomas (1974) is regarded as being of meteoric " origin, but .in one area the piesence of a halloysite vein istaken as _ - . G a evidence of possible'hydrothermal alteration. - 34/ " n ~~&$eret a1 (.19i9) besed their litho- explanation of the topo- \ graphy -developed above granites in Wyoming on the evidenc; of Precambrian alteration of one oE two granites. Precambiian high tempS rature oxidation of irdii-bearing minerals occurred during the late stage of crystallization I , $ of the granite., The oxidation occurred under the influence of high oxygen . > fugacity associa,ted 7.7ith an aqueous (hydrothermal) solution (i.e., a gaseous f phase,associated- - with the hydrothermal solution had a high oxygen con- c'entratibn) .' All i;ohp bearing minerals show some alteration. The alter- ation is regarded a$ making the rock extremely susceptible to disaggregation after limited meteoric weathering. The altered granite crumbles to g~;s 3 and give+rise to no bornhardts, tors or other positive~relief. These features fdrm on fie unaltered granite. From these cases it is apparent that while meteoric alteration , - of rocks might be the common case, the possibil.ity_of non-meteoric altera- 2'- k.", ti$n in a.landscape demands the careful attentiori~ofgeomorphologists, A , .: hydrothermal (including both a gaseous and liquid phase) and deuteric stage < . - are accepted as normal occurrences in the crystallization of a magma - conta'ining volitlies pnd distinctive products will result from each pkriod. % Different generations of solutions may occu5 within a single hydrothermal phase p&ducing dissimilar a1 terations (~ac6bs and Kerr 1965). cunningha& ,_ , .$+ L. - (1972) has emphasized" fiat the nature of igneous emplacement imprres . complex relations with country rocks. In addition to cbntact metarqrplFism this may include the formation of hydrothermal solutions. from primeval or m~teoricwaters resulting in non-weathering alteration. Non-meteoric alter- . ation may be subtle ~nddifficult to recognize, but may exert a profpund- . ;-= J . /'- - - e. 1 :. . Ad v C J 82. Q R - -I * influence oa subsequent weathering. ------t - Hydrothermal a1 teration may either be accompanied by distinctive (r mineralization or be similar to meteoric weathering. In the absence of I - ' distincti've mineralization, rec gnit3on of hydrothermal weathering is pro- / blematical. Konta (1969 .pg 289.) states "no methpd, in particular no ' F laboratory one, has yet beeit established to clarify the genesis of kaolin sand and to permit a valid comparison of corresponding resulgs obtained-3 for k different f ield~occurrencesw. Evidence of alternating so,_Y" d and rotted rock layers from drill logs might indicate only the passage through core- ,* * b -4 stones. While meteoric weathering should be reflected in a distinctive ' weathering front, subtle alteration such as recognized by Eggler et a1 (1969) will not be reflected in the absence of a weathering front. Evidence of non-meteoric alteration may be destroyed by or be ihdis- tinguishable from subsequent meteoric alteration. Any weakening of a rock will be exploited by meteoric weathering and should be suspected where anamolovs weathering is encountered. The possibility of non-meteoric alteration introduces a complex dimension into the topic of weathering in B genera1,and specifically'in-theorigin of deepweathering and weathering a&. residuals,'but the and assessment of of this type in a landscape is nor easily accomplished. ' Q J Petrol~gy ,F-- A hierarchy of weathering Susceptibility is present in silicate,minerals * ------and hasbeena topic of much speculation in the literature. The order was first developed by Goldich (1938) after a study of weathering an igneous rocks and is the exact reverse of the reaction series of mineral crystal- * .-< lization from an igneous < developed by Bowen (1928) as sh& in Table IV. 1 Y \ - 1 - 83. b 0 - - - .., . The weagheriri~is not strictly sequential but'the relative speed of decom- p- -- e '$ position and susceptibility to ;eather%ng decreases as one moves toward the final crysta~lizations. The series is comonily reported in the lit- erature with biotite and plagioclase alternating as the most easily 7 weathered mJnera1 in granite. Although this series is often regarded as being intuitively reasonable* on the basis of what de~eethe minerals are removed f rorn their envhonment of c,rystallieation, efforts at a theoretical - .!. - A justification of the sequence (and particularly the anamolous position of -- muscovite) have been unsuccessful. Table 1V.-Bowen' s reaction series. ' Olivine caC+feldqars Augite Hornblende Biotite - Muscovite -_. Quartz Strunz GI941 in Keller 1957) classified the minerals on the basis of '. 3.- I > -7 -9 the number of Si:O:Si bonds about a eference silicate atom, thereby _. . s indicating how closely the mineral.approac~esthe three 'dimensional tetra- , ' . hedral array of quartz in wLich banding-%i satZsfi&3 w6thout iritFijdu=ing - , extraneous ionC - The general order obtained (neosil icatgs, sorosilicates, , - cydosilicates, inosilicates, phyllosilicates, tectosilicates) parallels * PI \ ' 9 the order of Gol'dich with the obvious exception of puscovite and the feld- . . -g spars. Keller (1954) evolved a similar order .by calculating the ?nergieb - &. .F <- of formation for each silicate structure. Thesequence broke do&, however, when catio; links were included, probably because no assessment was included of structural factors-of the different minerals which influenqe weathering. Goldich's observations were experimentally verified by the work of i &- Baglord "et a1 (1963) who abraded minerals into distilled and carbonated waters, and recorded equilibrium pH values and dissolved ion concentrations. Those m&neral+-it&- a Lesser uea&hering stability had -higher abrasion pH -- values. The sequence changed dramatically in the C02 charged water, relating weathering susceptibility to the pH of the sol, and demonstrating that the system devised by ~oldich:(1938) is an oversimplification often not - representative of actual weathering sequences and conditions. A presentation and discussion of other work attempting to explain 'the susceptibi1,itjr'of / minerals to weathering is contained in Loughan (1967). The stability seA es reported from field investigations conf@ms the &4* 4- general series outlined above (see Hariss and Adams 1966, Nossin :";%nd;Levelt %+ 1967, Eggler et a1 1969, Oilkes 1973). The implications of the s3 ies are , twofold. Silicate rocks will decompose at variable rates depending on the type of component mi-nerals 'present, with granitic rocks,being less easily 'weathered than more basic rocks (diorite, gabbro, dunnit:)-, and minerals /J withing rocks will decompose at different rates resulung in disaggregation of , e +- * * the tock bithout necessarily invoking Srvasive decomposition, PH values . ' obtained from field measurements of qurface drainage waters 4&ye found .by - *S-%*------& -- - Keller (1960) to correlate with the rock type present. ~l~lnesurface " *J - -.- - - waters were associated with .basic intrusive~and vo1cani;s while acid val,yet, 4 &%*% were'associated with granite and gneiss. This again reflects the suscepti- ,-1-1 - - r bilzy of the .rocks to alteration and abrasion' pH values of the.constituent 4 minerals. The stability series is also ua&~l in explaining the association u i Although weathering residuals are reparted on a great varietypf rock i -- types: their Occurrence on coarse-grained granitic rocks is a pervasive 4.. i 8 i' I theme in the giterature. This has been recently emphasized by ~ho&as(1974) in his review of granitic landforms. The correspondence of rock type and . * =* I landform is not fortuitous but reflects a logical Qnteraction of lithologic ------and proeesa . -p - -- 'L $ - An earlier sec-tion stated that a hierarchy of susceptibilitq to , .weathering exists in silicate minerals and that the series can be extended. - '\ - to intrusive rock types. Basic rock types are more easily weathered than w."I, granitic rocks, but this factor alone is insuffiicient to explain-the lesser It occurrence of weathering residuals on these rock types since chqical *- weathering will behave in a characteristic fashion (production of spherical t v s=, form, joint guided attack) regardless'of rock type, A comparison of the , deep weathering of a gabbro with that ofSagranodiorite by Nossin and Levelt (1967) illustrates why residual outcrops are associated wLth graniti/c - CI rocks. The deep weathering profiles on the two rocks w&e qualitatively ;-*I ' . . similar but fresh rock was present--over a lesser vertical interval on the j' i - / * gabbro. Corestones ie~easedin the gabbro underwent fcomplete decomposition , soon after their release from the bedrock while granodiorite corestones * persisted throughour the profile. The- absence of minerals resistant to' weathering in the gabbro resulted in rapid weathering to secondary minerals and elimination of the rock structure. This rapid and complete alteration-.' ------ ; suggesfs complete reduction of the rock mass will occur even where joint spacing is wide,and that the first three zones of the weathering profile, (seefigure 7) will be present over a smaller vertical interval. This 3. different response of basic and acidic rock types to weathering may be - - - -ppp-p-p ---, ------reflected in the overlying topography. Nossin (1964) found basa1t.i.n " 8 I , LL Malaya to give rtsei fcaz example, to av&y-subdued topography while ps-x numerous hills and a ley regular relief was present on granite bedrock. & Granitic rocks consist of minerals of strong1 varying susceptibility i , . ,' to weathering (sharply contrasted in granites_$s the resistance of quartz ij/ and orthbclase to decomposition and the suCeeptibility o'f plagioclase, bi~titea+d hornblende). This indicates that chemical decomposition will '. i l -- mgranrtic rocks and increases tbet along which weathering can penetrate. These resista1 t minerals '\ also result in the retention of some of the structure a of the 'original rock (in corestones and pfeserved structures in the regolith, \ Oilier lb66b), leaving a record of .the weathering. This selective (rather P 3 than pervasive) decomposition of granitic-- . rocks promotes differential weathering and the retention of basal relief. In Malwj, Schroder (1973) '* found rocks rich in mafic minerals to be associated with low hills while rocks poor in maf9 minerals were associated with hills of substantially- greater relative relief. The contrast in relief is attributed to the 1 different response of the rock types to intensive subsurface chemical &'i ' A weatherin%/ prior to stripping of the landstape-under more recent climatic d conditio'd. In areas where chemical weathering is not the dominant geomorphic force, relief has been related to rock hardness and massiveness * I 4 these qualities will determine the res'istagce -to erosion lint 1963). areas of deep weathering the mineralogy of the-$ountry rock will play' ------ - r+ important role in the evolution of landforms. + - T -- -- Weathering residuals are comonly reported on moderate to coarse- > graihcd rocks i in ton 1955, Ollier 1960, Demek 19641, and in some cases the I distribution of residuals is explained by a change from resistant coarse- -C -e - "4. . grained to more easily rhahsed finer-grained bgdrock (Radwanski andLQUkr 1959, Eden and Green 1971) - Chemical weathering'is restricted to the , z dc~essiblesurfaces of minerals; and small crystals will havq a greater surface" area per unit volume than larger crystals. This in turn results in an increased susceptibility of fine-grained rocks to-chemical decompositiog. This general ielationship may be reversed, however, where a coarse-grained rock s.2; . e is more porous than a fing-grained specimen. Ruxton and -Berry (1957) have ------A - . % reported this revers5. relationship to occur in the granitic rocks of Hong ,I* ,I , P' Kang. The association of the rest'dpals with coarse-grained rocks should -. ,' be viewed as generaIly reflecting their lesser susceptibility to weathering. Micro-cracks, jointing and porosity may, however, be equally or more important than simple texture. These factors are probably variible and qre 9: 9: . difficult to assess over a field area. An important consideration is that coarse textured rocks under subareial conditions tend to evolve by granular : r disintegration, retaini& their original shape, while fine textured rocks -. are subject to greater resculpturing (Demek 1964a). This tend$ncy of coarse textured graniJes to retai chemical weathering attack. The sediplentary domes described in.'O.llier a@ Tuddenharn (T961Z and BracfIey (19631 are not XttributeitOadeep weathering- -- -- , arigi6 but ratfrer to subaretaf extension jointing; -Perigkacial Cars_ in -- d, sandstone are noted in Demek (196~)and Derbyshire (19721, and specialF + slope tors in a gritstone by Palmer (1956). _The dolomite tors of Ford (1963) < - were ascribed to a solutional attack on calcite in the rock. The gritstone B *- tors of the Pennines were interpreted as periglacial tors by Palmer and - ~adle~,;cQ62), although Linton ( 1964) and Cunmham ( 1965) have claimed , -, * 1; ',* ' 4. - them to be of a two-stage morphogenesis. Cement variation is often the . - '1 source of the differential response of sedimentary rocks to weathering i .- F agents, Sedimentaries, however, do not frequently give rise to tors or other weathering residuals. ,z Metamorphic rocks give rise,to both periglacial tors and weathering residuals. The metamorphic structures result in distinctive forms of the landforms in most cases, Gneissic and schistose rocks are less likely to , , give rise to weathering residuals because the numerous foliation planes and laminae constitute closely spaced planes along which wa-ter can penetrate and decompose the rock: The differential decomposition associated with mineral *AI banding in gneisses is regarded as inimical to the production of residuals G9 by Ollier ($960). Feininger (1971) found that residual bedrock remnants - were rest~~ctedto the very ba~eof the re&lith in metamorphics (gneiss, *L J* ? ; schist, ph;llites), and fresh roeexposures and corestones were only rarely encountered at the surface. Ollier (1960) found resistant quartzite bands formed ridges rather than true ikselbergs. 4 ' Where weathering residuals occur their form is strongly influenced by the metamorphic structures. The dip of foliation and apparent-4jedding in the Otago schist is responsible for the configuration of the basal sur- ~f$ face &d tor forms (~c~raw1965). "Fretted tors" and an irregular weathering f EOFI~occur where the dcp oS the foli&tion i~kt+bSeep,heas -- -- bLocky tors and a regular weathering fronr oc=ur where the schistosiry parallels the surface. ~h$remarkable ~~enitentrockst@ investigated by Ackermann (1962) are freestanding tilted slabs projecting from the bedrbck I' . P surface.' They are the result of differential weathering and exhumatibn of ,5,.'?i. < ., I: a steeply dipping schist. These schist tors are more susceptible to sub- - 7- aerial decomposition than those in other- crysealline' roc s. On B'different scale, Jeje (1973) has attributed the elongation and asmetry of gneissic - insclbergs to the foliation of the rock. He also found gneissic bedrock , '4 * to give rise to fewer inselbergs than granitic rocks, * 9 Periglacial tors carved in metamorphics have been reported from -. 1 Czechoslavakia and New Zealand. Frost shatteking is aided bx the greater access of water into the rock along foliation planes. Demek ,(1964a) and - -. ru Czudek (1964$':emphasize the lithologic, susceptibility of different meta- L .c mrpftic rock types to frost cation in their studiesof angular tors in . . ' Czechoslavakia. The significance of the crtrilte of resistant beds in the formation of chains of angular tors is cited by Wood (19511, itanen (l969), 'r X, Brown (1963) and Martini (1969). The dip of strata is related to the height . and symmetry of angular tors by Demek (19691, Dahl (1966) and Martini (19691, -- , and tors are common. where a bed susceptible to frost action (quartzite) L overlies more resistant %tra .+ schist andiare'absent from poorly metamorphosed schists or graywackes. The role of rock type plays an important part in the evolution of landforms under discussion. Coarse-grained granitic rocks .most comonly " give rise to v;eathering residuals, although weatheripg residuals may occur L in basie and fine-gra+ed rocks. ~'egmor~hicrocks usually are more easily am+ completely decomposed than Lgrteous rocks dtre-trrknterqx-structureq and---- weathering &$his type of rock does not frequently result in residual - landforms. t The strike and dip of bedding and foliation in metamorphic~is 3.- reflected in the shape of landforms evolved, Sedimentaries give rise to tors U? . - anQ&mes only where they havg, a massive structure that is r%sisi+t to F . ,a .s 1 - w . ?+. q- weatherink. The role of rock type, texture and internal structure is - -- -2 e variablb and the generalizations above maf not be reflected in a particurar landscape. 7- J r 4 f ?- ,.-.':I. Deep weathering -%p +* h An important characteristic of the deep weathering profiles described in the literature is that chemical processes and products (secondary minerald B ------are not the same throughout the profile. Environmental conditions change with depth as evidenced by zonation in the vertical profile. These' changes are represented by the type of secondary mineral present,with the inftial I r, .1 secondary minerals being altered as they come closer to a surface environ- 1 - ment (~ossinand Levelt 1967). Loughnan (1969) gives the e%*ampl& of a 'u- tropical profile where exmeme leaching leaves only insoluble sesquioxides at the surface. Silcca retention in middle depths allowed kaolinite to form,and mixed layer ciays are present at lower levels where still less ' . %* agressive leaching takes place. L The properties of $ill alsb vary throughout a regolith profile. Rainfall in tropical-areas is often alkaline (~horley1969 cites a mean of pH 7.8 in Uganda) because high temperatures and large droplet size restrict the absorption of atmospheric carbon dioxide (mid-latitude rainfall is generally weakly acidic due to greater absorption of CO and 2 fckrnation of carbonic acid). The rainwater may become strongly acidified in -t - - - - the CO charged soil atmosphere or in passine throunhde~@nposin~or~ani-c----s 2 d *. *. - matter. Acidity will decrease, dissolved ion concentrations increase, and-* - - - - - .- ; temperature decrease as chemical reactions take place while water passes . - inta lower portions of5thk regolith. ..At the weathering front the environ- mental ~h,pH and composition of the sol will be markedly different from the original characteristics of the water at the surface. The chemistry L------.-- of weathering, type of secondary mineral formation and rate of' &eathering at the weatheriAg front cannot be determin* 'through measurement of near . . ' surface parameters. his is substantiated by an analysis of changing mineral suites and geochemistry of a lateritic wreathering profile by Oilkes et d (1973). Experimental work by Baglord et a1 (1963) demonstrated that the solubility -- PAL A ------c of ions isLafunction not only of pH, but of the type and concentration of " -< ions already in sol.ution. This will obviously be an important ~5ctorin a weathering profile, It is:Gparent that within a regolith that "not one, J but a series of weathering environments exist superimposed on one another % with the residual products of each forming the parent material for the , new environment" (Loughnan 1969 pg 69). Weathering will change both quan- h -. titatively and qualitatively within a regolith and there must be an awareness of this in assessing deep weathering rates and processes. The-, b' . f . . great disparify in rates of weathering between tropical and mid-latitude areas is based on the total depth of known profiles and the degree of ' 'C alteration in upper horizons. Consideration of the weatherirfg environment 4 at the bottom of a regolith might show a greater similarity between I weathering rates in the two zones than is comonly thought. ! 1n;-&fi area of deep weathering, the weathering front is cownly % proposed as,a basal surface of irregular relief. Weathering fronts exposed in road cutsare irregular surf-ace~~a+r~i~l~l~rikingexampl~o•’~- this is described by Lumb 19621, but investigations other thansimple cross sections of weathering fronts are uncommon.. Only two thorough investigations of basal weathering fronts have been qadc, one in Colombia by Feininger (1979 and in New Zealand by Leslie (1973). In multiple borings through a regolith - , - - < '\ - - - - - J'------A- - - in a kchist area of New Zealand, Leslie (1973) determined that an intact e A - + --iiC - B regOlith?!y beneath a Pleistdeene p&iglacial mantleyand that the under- t" lying bedrock surface was an unexhuined tor landscape. The depth to the es weathering .front .y+s very irregular. A L{inea; altiration of deep and . . e shallow weatherkLwas. . noted and attribu ed tb asstructural andlor lith- ologic control in the schist. C I?eininger (1971) obtained sufficient data from multiple borings to ------A- draw a topographic map of the weathering I front zind- numerous cross sections. ', The boriQgs noted an abrupt transition •’40; weathered to fresh rock in a -5*' f s- 3-6. ft interval. A number of Csolated closed basin 'depresiions existed I innthe bedrock. The thickness of the regolith ,was greatest under. , hilltops and decreased towafd valley bottoms. Feininger regards the data, although 6" from a small area and a limited number of borings, as broadly representative of weathering front topography in deep weathering landscapes. The data 8 presented by Feininger 61971) and Leslie (1973) confirm earlier speculation about the i&egular relief of the weathering front. A final aspect of deep weathering is that it may result in both qlti- ?..by - convex and multi-concave landforms.~homas1974) producing an etch plain landscape of closed or partially ~losedb-ins (Thorp 1967, Feininger 19691, . &,*" .>' or tor/irkselberg landsc,apes of a variety of types. ~n.$&.ellent discussion. , . i, r\ - 4: - is contained :in Thomas (1974) who shows that landscapes produced .by deep i- weathering and stripping are not limited to those dominatgd by weathering : '. '. residuals. - * ------ Climate + - f As a prefacqd discussion of the influence of climate. on weathering, -: 6. " -" - the unique role of water in weathering processes must be'r-estated. The r, . . . $1- - presence of tmtm Is the eritie& facCw i&-c-hieal we&k~& as ~t 1s - , -- a mai6.r reactant, the,sol in which other reactions take place, and as the --& .P ', /' - transpdration agency of decomposing agencies and soluble weathering products .' Circulation of groundwaters (or ionic diffusion as proposed by Leloong 1966) , *is important in preventing the establishment of a chemical equilibrium. kll i' i' ;ocks show definite instability when in contact with met-eoric waters. The 1 intrinsi-kage of chemicd weathering with water suggests c1imat.i~-and --- 'local hydrologr'c factors will strongly i.nfluence ieatherjng rate,< intensity -and type. Temperature, pre~ipitat~on,relief, n and drai3age will # - - strongly condition the weathering environment. > 0 A 10 C rise in temperature will generally kesult in a 2-2.5X increase C '. / in the rate of a ckmical.reaction. The rate of chemical weathering Q *. reactions will increase with a rise in annual temperature. The disso- ' . ciation of'water into the component -ions increases with a rise in temper- ature, resulting in a rise in the inherent reactivity of the water. Lukashev (1955) reports the relative dissociation of water into protons and hydroxyls with in=reasing temperature as follows in Table V, postulating . - that the greater availability of hydrogen ions in warmer groundwaters is . a significant factor in weathering over geologic times.' , d T*able v.--~elative dissociation of water with 0 Temperature C o0 lo0 18O 34" 50•‹ , .& d i,: ~e1ative;~issociatidpn --1 1-7 - 2k4 - p------4.5 8.0 -- (from Lukashev 1958 pg 65) L T- - The gr&ndwater temperature will be close to the average annual temperature i, ., of an area. The speed and inct&nsityof reactions can both be expected to rise with the kncrease of tAperature in an area. * ~iologicactivity alsd~increasewith rzsing -temperature. ,fie" . . \i' '. weathering' agents dirived from the decomposition of org&ic d&is (l'-liumic ' T acids1'). will form at accelerated rates in warm environments. Although'the . \ organic content of soils decreases exponentially with increasing temperature 1 \ , L (~enn~194t), the net biomass produced and decomposed will increase with a rise i'n biological activity. This will result i~ a greater generation of . decomposing agents and morezggressive weathering. Despite'the fact that - -- -.- 3'- - - chemical wemathering- will be favored by in&easing temperature, Gther.effect9 1- bfh,temperature rise may act to offset the increase.' This might include . , increased evapotranspiration, a decreare -in vegetation due,to moisture stress, f; and a decrease inthe production of carbonic acid by solutioh of atmos- d , pheric carbon dioxide in rainwater. All of these factors contribute to the I low intensity chemical beathering in arid afid semi-arid areas. The v- solubility of carbon dioxide in water is sensitive to temperature change', - \- decreasing with risug temperature. Cool areas would generally be more ~fkb$?$$~ charge with carbonic acid, which is extremely important in.the ii -. weathering and so1 ution of some ions (plrticularly calci-urn). Ollier (1969) . . has pointed out' that d decrease in temperature iay limit vegetation and carbbn dioxide in the soil atmosphere,resulting. in a decrease in carbonic x- . ,. Xcid. To this writer's knowledge, quantitative-%gSessments of the role of temperature and vegetation in chemical weathering have not-been undertaken. Temperature increase has traditionally been regarded as speeding the t rate of \solution and raising the eqn-irI-irb~-cmcerrtratio~~~sil~ca-ina- 7- 1 1 Q-m sol, Tbsez. -has been regarded as an important factor h-t the leaching of quartz and the forinartion of a sesquioxide rich upper horizon in tropical areas. Silica mobilization was found by Davis (1964) to be uninfluenced by E * // - 0 pH, climate, vegetation, or temperature below 35 C. A simple relationship " 9 does not existkbetween 5hemical wea.thering,and temperature. Temperature - =- i f - a rise wihl speed reactions, but it is probable that other factbr-s are,,more - * i important' in governing the rate of chemical ~eath~ring, ""*+' L Precggitation is obyiously of enormous importake in chemical 4 --. weathering because it is the source of groundwaters in most areas. The *a B type of clay formation in the Hawaiian Islands has been strongly linked to the annual precipitation in different locations by Tandeau (1951). A d ------PA - -A - - - similar linkage of precipitatiqn and clay type was investig:ted in California by Barshad (1966). Other writer, working under a single climate, have linked the characteristic clay mineral to the underlying bedrock (Nossin ; F s and LeveQ--1967, Plaster and Sherwood 1972). Weinert (1961, 1965) A. .' empirically related the e+apotranspiration ratio to clay mineral type and .. -2- ..c -2 the relative domikance of -physical and chemical weatheribg processes in Although definite relat~ohgci~shave been established between weathering and a climatic parameter in these cases, the conclusions reached . -. -1 have not been si=cessfully applied in other areas. The general applica- bility is limited because the various criteria utilized inadequately i describe weathering conditions in the subsurface. The degree of leaching in - a.. :i? the subsurface eW%sonment, including the total amount of water infiltrating and flowing through the regolith, best integrates the effect of a n4ber of importa t environmental factors and constitutes a natural measure of the I weathe i g thvironment. Loughnan (1962)-- emphasizes-- - .the-importance------of - - S 4. leaching in chemical weathering,ahd in a later work stated: - ---- Undoubtedly the most im3ortant single factor control1ing the rate of breakdown of parent minerals and the genesis of specific secondary minaads is the quantity oE water leaching through the weathering e&$r'onnent {Loughnan f'$@ pg 49). . a- 5% &, -C I A general association of clay mineral type axLintensi ty nf Lea&in&wtx---- I, u reported by-~eller( 1957). He regarded the degree of leaching, td, the = exclusion of all other fictors, as determi~ingt& final stable clay mineral. This is attested to in work by Shermp and Uehara (19561, who repqfted that .r.9; -4 r kaolin it^ formed in free-drainage conditions on basalts in Hawaii, while f.. mon tmorillonite formed where drainage was impeded. Similar conclusions - dl were reached in the granitic rocks of thk Idaho bgtholith by Clayton (1974L -- - - i TPLp---- e Assuming sufficient prec&itation, permkabil ity &id time, it is a . apparent that even the riiost stablg of minerals will* be decomposed as all 'have 4 a. -. I/ --I &. 9 - 2 - a limited soldbility. :Quartz is'v excellent,%smple of this fact. Despite 4 - *. " -- * its extemely low solubility (12 ppm, about one tenth the solubility of .. -amorphous.. silica released in the wezthering of other silicate minerals, see Pickering 1962) it is commonly removed from the upper horizons of- tropical m* soils. A striking cyof this is reporred from Australia by *Bayliss and Loughnafi ( 1961) where a kaolini-* te sandstone containing 90% quartz was intensively leached, leaving-a &s idual layer of sesquipxides -which contained Z only 5% quartz. Pickering (1962) and Davis (1964)-both concluded that the rate of silica removal and chemical processes do not limit- the formation of P . latdrites to tropical areas. This suggests that weathering processes and Q products are, to a large extefit, independent of climate. Dennen and -, g-. Anderson (1962) reported that incipient weathering of rock results prin- . 3- 4 2 cipally in' an increase in porosity, and note the primary controls are the u- ------p 1oca environment an& mineral assem3ly presenTThey stated: . - Climatic factors A major conclusion of experimental work by Pickering (1962) was that the results obtained: ,,,indicate that theldi+i~*olutibn reac~n~~a~ocksar~ essential1y)the same r*&g%rdlessof tempe~ature,and should dispel any idea that chemical weathering processes are differetit in the tropics than in cooler- cl5mates. The chief beneficial effect that high temperatures- haye onTchemical weathering is to speed up disso'lution reaction& which can tak"e place in aqueous golutions at any temperature. Chemical weathering should thG be more rapid in tropical climates than in cooler climates, if o@er weathering factors ark equal, but no kifferent in its manner ?f progress / .(~ickering1962 pg 1197). -.p d The absence of climatic bias in weathering reactions suggests that - -- deep wea&hevring cannot be regarded as a zonal (c.e., tropical] phenomena." s Q ~t&khov ( 1962) developed a zonal distribution of chemical weathertng in ,- tectonically inactive areas (see figure 8).' Factors included in the analysis are precipitation, evaporation, vegetation, and mean annua+-temperature. .Chemical weathering is maximized-in tropical areas due to the combined - maximum of precipitation, temperature and vegetation in* this zone. A Y. secondary maxim% occurs in the mid-latitudes,, while desert and polar zones * . have little chemical activityfbecause moisture is'absent or 'is locked up .- in €he solid form. Figure 8 indicates that dgeply weathered-regoliths ars. L C expected features in either tropical or mid-latitude areas. Although marked differences in the rates of weathering will exist because of.-. climate and relief factors,'Lri the development of a regolith cannot be restricted to Deep weathering ~rofilesare more common in tropical areas than the nih-latitudes for several reasons. Intense leaching aid chemical activity is promoted by.the0 high precipitation and warm temperatures and results in A ------P< -P - . " rapid deco.nposition of bedrocl:. Moreover, many parts of cont?#ental areas - -- Q in the tropics have been subjected to these energetic proceF>cs- . for a very long tine, even very long in the geologic time scale. Perhaps more impor- - >*. tan s * - Y ------changes to aridity which resulted in the stripping of weathered mantles. L - z -- - - 2- he absence of large areas of intact regoliths in the mid,-latitudes is nb "- -* - indication that they never formed, or that they will ndt form under current / t. * / conditions. ,~onclus$onsalready presented in this section regafding the < absence of a linkage of climate and prpcess, and2stressing the importance ,/ of leaching in the rate of weathering, support Strakovls yc~nclusionthat I deep weathering could be both a tropical and mid-latitudeV.phenomena. *- The only condition necessaryfior the formation of a weathered regolith ,r i - / is that chemical weathering produces decomposed rock faster than.erosiona1 processes remove regolith material. Deep weathering is favored by the \ -. && combination of moderate to heavy precipitation with a tectonically stable, -.. i* L,low relief area in which erosion is minimized. In view of this it is not surprising that deep weathering is best developed in cratonic areas of the Deep weathering {profiles will' develope more slowly in mid-latituhs - I f than the tropics not olt.2~because of the lesser vigor of chemical weathering %- .. \ and slower production of $ecomposed rock, but because erosional processes f -. (which can be assumed io remove constant amounts of material bver a' given time period) will be relatively more efficient. This in turn, will result in a lesser net gain in regolith depth over a given period in mid-latitudes - when compare.i with the tropics. Also more time will be needed to reform a a regolith, in... the mid;latitudes following disturbance by tectonic uplifts, , , A furthgr factor supporting the procdduction- of -a -differentially - , :I weathered 1andscape.in nid-latitudes is that deep weathering may occur with- out pervasive decomposition of the rock if it is susceptible to mechanical disaggregation after limited chemical alteration. The disaggregation - would allow further penetration of water and weathering. Wahrhaftig (1965) *.F- - -- ., .. , reportgd,thafburied granites disintegrated rapidly to g$s after only 3 *-d - 2 slight alteration. Some wentherGg.of plagioclase was present, but the ..t- beakdown of this mineral instigam the mechanical breakdown of the rock. . . '-. .'y: ' ". -A The tendency of coarse textured granites td crumble into gr% after r ------minor alteration of mafic minerals (particularly bio~ite) is reported by Blank (1951rtl3, Melton (1965), and Oberlander (1972). Eggler et a1 (1969) .< ! - , state that the alteration of biotite to clay minerals resulted in egpansion - @ that shattered the otherwise fresh rock. The particular susceptibility of 3;% the biotite to weathering in this case was attributed to Precambrian= 'I alteration. Dumanowski .(1964) ycgard;' biotite as being particularly >*"- ': impor tint in lowering the resistance df granite* to weathering and promoting 3, granular disintegration. Coarse-grained granites with accessory biotite " % - seem particularly susceptible to disaggregation after limited weathering, -1 - &us partially explainirig their common association dith weathering~residuals. > * In these cases the rate of weathering penetration will substantially exceedthe degree of decomposition present. . # Deep weathering profi-les and r,egoliths are reported from widely dispersed areas in the world. In mid-latitudes they are commonly regarded - * as reli-ct deposits because radical ~ListoCeneClimatic changes and the sher t ~olw&teinterval a~epresumed ie -pre~hd+;ke ir-&EW%R~-f OZ~R~-~SF~:I+~-- * the Quaternary, The regoliths are often regarded as having_formed-under or - to be indicative of Tertiary tropical climatic conditions. Bakker and Levelt (1964) associated the clay content .of rAioliths with particular climates. A 15-30% K6olinite/gibbsite or kaolinite/illite clay content + I - pp -- - -- 101. - + d. was regarded as reflecting a tropical or monsoonal climate, and a low c n c2-7%) clay content to reflect a mid-latitude warm climate with rainfall C -=-, between that of Mediterranean and Gulf coast climates. The origin of the sandy weathering is much less certain, particularly in view of the pro- d C - + ; nounced susceptibility of some granites to gr& formation." Problems of ,interpreting the origin and age of regoliths are dis- 5 cussed trr Thomas (197%). TWse include the posdble-e-ects of-hydrothermal 4 + - or other paleo-weathering, the effect7'of pa;en't material texture and com-: - 3F .* position, ,the position of the sample in the original profile, age and degree +- -, of development of the profile, and topographic position. The dominant clay mineral type may be an indifferent indicator as it changes with depth pro- files and is largsly determined by leaching ~onditions. The-mjneralology t of profiles from different areas confirms a general absence of diagnostic : i. characteristics (see Balcker 1960, Leith and Craig-1965, Nossin and Levelt 1967, Oberlander 1972). Lateritic horizons are ';heoretically not limited to.tropical areas (~ickering 1962, Davis 1,964), and the traditional as,s~ci- * T ation of tropical clifiatesand reddened horizons (van Houten 1961) is * er questionable as in situ ,;ubification of alluvium has been studied in both I arid and trdpical areas by IJalker (1967, 1974) and Van Houten 0972). Both the diagenetic* rubification studied by Walker and the post depositional > dehydretion and oxidation of sediments described by Van Houten could con- ceivably result in the development ofLa reddened zone in a weathering pro- p-p - - p - p - -- p-- 'file. Thomas (1974) proposes the nature of etching on &art2 grains as a significant indicator of climate (see Krinsley and Donahue 1968, --# 6. Doornknmp and Krinsley 1971). The method is not sufficiently established, howcvcr, for a definite appraisal of its usefulness. ,xi- > * The great diversity of climates under which deep weathering has been reported (tropical: Ruxton and Berry 1957,-mid-latitude humid: Leith and F Craig 1965, semi-arid: Oberlander 1972) suggests that, in the absence of other evidence, weathered profiles should be interpreted as indicating only. ' *% * '. l a comparatively greater ecfficiency of subsurface weathering than surface erosion. In particular they should not be assumed to reflect tropical conpitions. Oberlander (1972) notes that the deep weathering in the Mojave ". ,? / Desert could be possibly explained as a consequence of time alone under the a ------present climate. The existence of calcrete horizons marking the, limit of pgr I current moisture penetration is .taken as evidence that little p'enptration of the weathering front is occurring. Certain profiles were radiometrically a;? Q dehonstrated to be of at least Pliocene age, malting the paleo-nature of the profiles undisputable. He regarded the weathering as having occurred under a semi-arid climate which as "nowhere conducive to the formation of true 1a;eritic weathering profiles of the type found in the present arid heart t ' - '% of Australiatr C~bgrlander1972 pg 11). Eden and Green (19L/l)&Tport the - ' w . x.9- ~ar latitude weathering "...it seems desirAle to avoid too direct an analogy with granite weathering processes in humid . .tropical areasM d den and Green 1971 pg 98). i This evidence' stpports the concept that dee6 weathering is not a zonal process but iS a function of weathering intensity, erosional efficiency and \ time. The interpretarioa of regoliths as-Tndlmtors ofc~icccOnidit~iOns -,2- v is hazardous and shortfd be avoided unless supplementary evkdemce ispresent. - Deep weathering profiles.wil1 be more infrequently met within mid-latitude areas because of the longer time period needed for the e,stablishrnknt' of a weathering profile, and the strong disruption in areas vihich have undergone x, : f~4e%stoeene glaciation or recent tactmlic uplift.-~6~rtemporar~ doep T - weathering on the Atlantic piedmont is cited by Craig and Leith (1965) and - - '3~- +,. *.a %,>-' Kessel (1974). A consequence of the inadmissibility of deep weatG&ing as 1. 'k .-; an exclusively tropical process is that tors and other weathering residuals- - are azonal landfor+, not only in distribution but in genesis. In-mid- latitude areas the greater efficiency of fluvial processes suggests a greater role for them in the. evolu~bnof the landforms. - This-is-demon--- strated by,Oberlander (1972) and Kessel (1974) who describe forms delimited by fluvial processes, but in which deep weathering has played an important .+. role. Tors and other weathering residuals must be regar&ed as azbnal land- _ ," forms having a similar morphogenesis under a variety of climates, and as, resulting from different combinations of weathering and erosional processes. ". The landforms of granitic terrains ~&,tenfw~'compartmenta1ized land- scapes showing the strong influence of the jointing pattern in the bedrock. Zn a deductive analysis Linton (1955) emphasized the strq~turaltT =-. . control of subsurface chemical weathering and the spatial distributiorLof the residual landforms. The differential at@&k at the basal weathering front was envisioned as reflecting the spati#svariation of jointing in the underlying bedrock. A greater significance warached to the vertical jointing than to the horizontal fractures. This interpretation resulted in an elegant and ------logical morphogenesis of the'fors examined, and allowed the theory to be . - - extended to other areas and landforms (0llier 1960, Mabbutt 1961, Thoyas 19651.. The great significance given to jointing demaiids a careful discussion of its origin and proposed role in deep weathering landscapes. - L 14 - 7" Joints are natural fractures of brittlg failure along which n?. . .. 4- tm - ' v - %- ,,-L - -A i' -, ------ appreciable displacemerrfz has occurred. Brittle failure has beepLtbe subjest - '-&- -- - -. 9. 1. of exhaustive stdies by civil enginkers, mater-ials scimfists and griologisk . *' A theory of stress, strain and brittle failure in crystalline solids has A' 24 ak - *',? . been developed and applied to ,crystalline rocks., - 'Rocks act as brittle - - ,?-gC I &- solids under surface or near surface conditions, deforming elgistich?ly up i * to a threshold value at which brittle failure is initiated. An excellent *' ,L treatment of the topic is contained in Price (1966). An explanation 'of the - ;+ ------A -- - - ubiquitous, three-dimensional jointing network found in plutonic r&ks .A might be as follows. %, I Vertical joints commonly aris; due t8 lateral extension of the rock mass on uplift. The lateral extension puts the rock into tension, brittle fractures developing where the stress exceeds the tensile strength of the rock. This stress 'is pan-directional in the horizontal plane and fracture would be expected in at least two mutually perpendicular or subperpendicular . joint sets. Regular horizontal jointing is again a tensile fracture and is instigated by the remddload~ingon the rock. A plutonic rock crystal- lizing at depth will be in equilibrium with the pressure conditions of that environment. Removal of the overbMen results in adjustrkent to the new .& i pressure level, the roJck expanding normal to the former axis of loading This type of fractu:e, where there-gno active tensile stress, is termed an extension fracture by ~illings(1972),. A mechanism exists •’0; tfi"eevelopment of the regular three dimensional i joint network commonly reported in conjuwthn-et-frweathe~kg-resgduals. 't It is notewor$$y that tors are not reported from areas where the jointing is irregular. Obcrlandcr (1972) reported that in areas of non-drthogonal jointing irregular blocks, walls and pinnacles were present instead of goulder-mantled domcs and tors. Variation OF this (type, occurring within h* 3 , ..- k +- or in lieu of a regular rectqngular joint network, can result frdPamany eL 4 /' - -- - factors and is frequently thought to play an important role in the develop- *."-. t ment of a weathering landscape. * Rock is not a homogeneous, isotropic solid. This prevents the direct application of fracture theory, to rock masses. ~hresholdspf brittle . \ 1 *' *. failure may vary within a rock mass and stress may not be equally distributed Rock characteristically fractures.at stress levels many hundreds times less ------than its theoreticag strength "due to microscopic flaws within crystals (this is the Criffith theory of brittle. failure). Differential uplift, . .-- - - - 'erosion and tee~nicstress complicate the simplistic model of joint 2. U& , - development outlined above, and make it di'f f icul~ti6 ascertain the origin of -- It . I* a particular joint set. Twidale (1964) cited empirical'evidence of the i - presence and jrregularity of stress in granitic rocks and emphasized the rple of such stress in explaining joint systems. The variable tendency of . domes to undergo .extension (exfoliation) jointing was attributed by Blank (l9!la) to stress differences in the bed;oct. ~ieldmeasurement, of residual stress, however, is usually not feasible. The variability of joint density was prbposed by Linton (1955) to be I - a major control in the morphogenesis'o? tors. This position has been widely accepted in the literature. Although there is no theoretical objection to -' " -, ,- the existence of irr'egular joint density, there 'is little empirical evidence that it exists in tor areas where it is proposed to be atmkj,er control. 'l. - * Measur went of jointing is difficult because ofpoodrsposur &oLthdedrocl~-- surface in most areas. A difference of joint density between two focl: Spes " was observed by Kaitanen (19691, and was j:dgcd to be responsible for core . x boulders by Thomas (1974). Twidale (196.4) cited a case where joint density - between a .domc and the marginal area was pr¢, but stressed the .. . % .* t*? . I - D- .; 4 106. ------k- orientation and openness of the joints as wella+t&+athesAdeity. M .- The steppcd tosography of the Sierra Nevada was found to be ynrelated to the underlying joint patterns by Wahrhaf tig (19653, while- Oberlander (1 2) ,, 9 found no aQpreciabledifferences in joint density in the dome, boulder and, v r - 2 * tor landscape of the ~oja;? Desert. Cunningham (1965) questioned impor- w..&e ,.. 1 tance of joint density in the origin of the Pennine tors. ,* - Y' In an analysis of the role of joints in the production of tor - - - n- landscapes it must be stressed that it is generally very difficult to v empirically measure joint systems. This arises not only from the incom- plete exposure of bedrock but because: ...in the field only those fractures which have diilateck suf- ficiently to be detected can be recorded. Tightly closed and incipient joints are passed -over unknowingly (chapman 1958 pg -532). 5 Twidale !lQhL) dre:,~ attcntion'to the character, rather than the density of jointing and stated: e Despite superficial appearances to the cdntrary, most gianites are well jointed: it is the tightness or openness of the fractures that is significant (Twidale 1963 pg 51). The role of joint density in the formation of tor landscapes proposed by Linton, while both plausible and possible, has nok been conclusively' - -F established at any deep weathering site or in any exhumed landscape. Linton' s deductive -hypofhesis,has been uncritically accepted in most lit- .. .. erature accounts. The influence &€,jointing should be placed in terms of joint openness rather than simple density as it is only along open joints ------&t- .water can penetrate, Thiimas (1974) h-as proposed that other factors %- may be.responsible for the variation of the weatherin'g front, including micro-cracks (~isdom1967) and potential jointing (chapman 1958), both of 50 -.a;- nhich would increase-the porosity and weatherability of the rock. i ?- A more definite relationship between jointing and deep weathering is (~ing1946, Hilton 1966). ~hikrelationshi; is succinctly stated in t%e k' following quote : The ultimate depth of,weathering may be that depth at which the lithostatic pressure is sufficient to make the rock impermeable or so tight as to effectivelwrest the circulation of water through it (~eininger1971 pg 66). -* The vertical loading on a rock mass rauses a lateral expansion as well as ------L a decrease in theLvertical dimensio* of a rock mass. ~his;last%~ defor- .. mation may be sufficient to insure that vertical jointing is tightly closkd + or latent, preventing the penetration of gr'hndwater into the rock.. The closing,of micro-cracks and joints may be related to stress having an origin I- other than simple gravitational loading. It must be noted that theTz basal limit of weathering pene,traeion is not fixed. Continued de~ompositio~~of r fhe bedrock,or elimination of part of the overlying regolith will result inL . . either thg-opening of tightly closed joints, the extension of existing , 4 4/ 4 joints to nh depths, or the opening of lat6nt jointing in the rock rna'ss. , \ 1 Alshough the relationship of deep weathering and joints is no: a&-r h *:..'% simple/. as was envisioned by early writers, there is no quB=k&.n thatu- jointing does exert a profound influence on deep weathedng and residual landiorms. Tors, bornhardts and domes all exhibit the profound control of ,. c3J" jointing. Twidala (1964, 1971) considers- these features to be structural 2 i., landforms and stated: * Structure'determines the morphology bf.granite terrain: where ------the jointi~gis massi~e~andtight, domed inselberks develope: where the jointing is moderately fine or open, or both, tor land- scapes are formed: where the rock fs fissured by 6pen joints;'no typical forms develope (Twidale 1964 pg 110). This classification of the -features as structural landforms is untenable. .because of'the substantial role of weathering processes in the formation of these landforms, and the probability that fn some cases form determines ------joint structure (chapman 1958) rather than the reverse re1ationshi.p. Micro- i 1 .. structures may,'be imprtant in the initial isolation of a tor by weathering agencies and play an important role in determining morphological detail. 7.. -- . * In some cases, however-, joints &I take such a dominant role that ;he land- + - 7 ,-.. - w forms are structural in origin. + > ... The grigin of domes is 0f:pXrticular interest as they ofteh dominate " ------?+ - - landscapes inCghich they occur. Thomas (1965, 1966) and Twidale (1964) have proposed that the broadly concentric sheeting fractures of sorrje domes is ", .due to the isolation of relatively unjointed masses in the subsqrface, followed by extension jointing (e~foliation)s$mpathetic to the subsurface form. Massive or tightly jointed areas are probably indicative of areas where latent stress is present, providing %mechanism fol;,,the extension jointing. Thomas (1965) proposes that volume loss,and loss of rigidity in the surrounding the dedlopment of extension joints, due to surface may also be -\ favoring further development and retention of the domical form. Continued - 1 weathering attack would be guided along the sheeting networlqand the.sub- surface evolution would consist of the $uccessive formation and decom- -5 . .. position of concentric shells, insuring survival_of -the form until exposure at the surface-as a dome or bornhardt, ------. ', The uniq%ierdle of jointing in the development of domes must always T zi . be acknowledged. Although the morphology of meso-scale landforms such as * tors is easily explained by a strict chemical weathering genesis, the difference of scale of bornhardts and domes suggests that too stringent an 3 . I *ia,* application of a weathering hypothesis is both undesirable arid'krealistic. A ------Doqes and tors can usually be distkguished from one another bji,thei-pre- @l * sence of :bxtension (egoliation) on 'the former, while' tors are weathered joint blacks. This distipction, while gknerelly viable and useful, becomes 'Z tenuo3s when doniPa& joints are regarded as e::ten:ion joints developed -&;- -Gter the isolation of m%~ivi blocks by subsurface weathering widal ale , k &** - - 596.4, Thomas 1965), and where large rock cores occur on which sheeting is , . Cunningham (i971) has suggested that some bornhardts may-be forms w i inherited from the emplacement of the roof of a pluton that are subsequently C exposed by erosion of theJ. - overlying country rock, Primary joint structures in this peripheral zone of a pluton due to cooling and continued magmatic 4 movements have hem described by Balk (19371, and may figure* - in the * evolution of later landforms. Kranck. - (1957) has suggested that structural =<* domes may result from the conversion of vertical stress to radial corn- - 4- pression- while Twidale (1964) states that repeated intrusion ran result in - * domical forms. Domes can hgve complex origins and are excellent examples of convergent landforms. The fact that jzinting commonly follow6 the surface d configuration of the dome has resulted in much speculation as to'whether t the sheeting joints are the cause o? the conseqmgnce of the dorni<=l form. The parallelism of topography and jointing has be& noted by many , writers (~ahns1953, Chapman 1956, Chapman and Rioux 1958, ~radley1963, -- Twidale 1964, Kack 1966);'anb jointing has been ohser~eb_to_b~uninfluenceh~~~~- _r: by geologic contacts, dykes, xenoliths or pendants (~ack1966,Thomas 1965). . #- P *a Chapman (1953) stated that massive granites possess many plane.wf potential x..- x..- 9- b' jointing and that actual jointing is basicals of->surface origin. At each EL* 4-- field site only a few of the potential joirtt~setsduld be actually r 9, . , *, - &f expreqsed,- those whose dilation was faccfrted by the- txgraphy of the ar"ea. A& L* e ' " . This- qxtreme relationship of topography and joint-ing would make domical a "-8. e \ , 'p,,.- joint structures dependent on the previous existence of a suitable hill r " 2 form. A similar concept was presented by Gilbert (1904) who regarded the ' .& *. extension (exfoliation) jsinting ti% be due 10unloading of a puperincuhbent Jr . # -, load with the d~&~:reflect'ir&*a 4ormer topographic surface. Domes arc - * figarded as structural l~.ndfo&s by Twidale (1964) who stresses# the ------LL - - - 3 exisfence of radial compressive stress in the horizontA1 ~l&eas,the major t +--. L- ' I ' factor in their development. It was suggested by 4Jhite (1945)' that. domes ?-. t L - could result from a non-directional denudational at&ch (in this case *,' - C 4' granular dipintegration),while acknowledging that they could be produced by a variety of processes. ' ./. If residual stress remains unrelieved in a rock mass under sub>eri.al 6 J '4. 4. conditions, the least stress component will normally be atmospheric pressure . . and perpendicular to the rock surface at all points. Latent stress would be . . reli ved by extension jointing on varying scales, which would be roughly t P % parallel t? the- rock surface. ~maliscale arching of the rock surf~Binto "rock blistersn has been noted by Blank (19511, Corbin and Twidale (19631, - Hack (1966) and Leigh (1968). Spalling on a still smaller scare was noted ' by Blank (1951). The effect of latent and form-induced stress in the 1 weathering of rocl: masses has be& emphasized by Gerber and 'scheidegger (1969. The stress'es due to these two factors may act alone or in conjunction with 6 other weathering forcec They argue that stress c-fiEnsmay triggek tTi, -- r"- 6 - &velupmeftt of features rtomalf g attributed strict1y to other -athering .processes. /" 6 f Extension jointing on a large scale is the dominant process of cfenu- dation on domes. Jahns (1943) found sheeting.to become less frequent and more horleontal with depth in quarries,and Mabbutt (1952) proposed that F== - - --- dome6 would be reduced in reli$f by the shedding of sucFessively more hori- , ' zontal joint sheets. However, Matthes (1930) found sheeting to be repro- ducing itself in,concentric shells. Again no consistent behavior of - -* jointing is apparent from li*terature accounts. Hack (1966) noted that higt' angle joints decreaged in number with depthUand that abrupt changes in ' i- their frequency occurred from sheet to sheet. This indicates that vertical - - -- I - B joints may be, in some cases, subordinate to extension jointing. This would 'A account for ,the corestone, joint block, exfoliation sheet, unweathered bed- rock sequence observed by Mabbutt (1961) in Australia, and tors superincumbent on domes hornas as ' 1962)'. Chapman (1958) proposed that gravity-induced weep 91 .dl C. would favor the opening of latent vertical jointing parallel and perpendi-- culzr to the direction of movement. Joint sheets are commonly observed to - * . .$& ' be divided and destroyed under subaeri'al conditions by the opening of latent vertical jointing, confirming the importance of continued dilation under A subzerial c~~ditions.: . .- ,- d ~homas(1965) regarded bornhardts as resistant to subaerial denudation, :. +' 9 attaining prog&&.sively greater heights as, the to$ographic surface is lower& -r by erosion, until latent vertical' jointing is opened. This results in the collapse of the bdrnbardt into a casile kopje. As the unsupported height of a rock mass increases, internal lateral stress will incr.c-a&'. - due to ,.s gravita,tional loading. Extension jointing normal to the vertical loading . + 4 - ,,- ~roulddevelop , either opening entirely new joint planesor 'exploiting latent, I 1 vertical jointing. King inplied this, stattng "as horizontal preSsure & r pC * ' be increases with depth there trf1L be a cGitica1 height beyond which any . *_ natcrial cannot Stand unsupported" (~ing1958 pg 290). Thomas notcs the I& irregularity of h5ight.s at which the collapse occurs. This is possibly due M ------,---- -. - - to variation ii.l>ent stress:and- A jointing i conjunction with gravitational loadhg, resu inconsistent levels. 9 1 is & I. Jointing plays an important role in both the subsurface and subaerial evolution of weathering residuals. The common ascription of irregularity in the weathering front to joint density, while consistent with both joint theory and weathering behavior, has not been conclusively demonstrated in -- - a field investigation. Joint openness is a more significant measure of the role taken by joigmng. As well as this passive role in guiding subsurface 4 weathering, jointing may be a dybhiic force in &eterminia$ both the morphology b and subierial destruction of weathering-residuals. The interaction of latent and fdrm-induced stress proposed by Gerber and Scheidegger (196%) suggest th~ttho "~~in+ing.-~c~!~~nl~mstlmay operate on scales nbt commonly , associated with jointing. Stress and brittle failure will be a principal % controlling factor in any deep weathering 'and-exhumed landscse. . Subaerial evolution . l .-I - A distinctive characteristic of weathering residuals is the dicho- tomous behavior they displ-ay in response to subsurface and subaerial weathering processes. The, features are transitory in the subsurface and would be ultimately reduced by chemical weatherini unless exhimed by a* . - erosional processes. The features are relatively immune to subaerial watltt-ring agencies and evolve sfowly~overlong per~ods,iu~ivinitobe = + - 2. Q > eJ distii-c t ive features of greaE antiquity in eontcmporary+andsmpes.- Tkis is .e:+- - best explained by comparing the subaerial and subsurface micro-climates. 4' While ciiilosed- in a .regolith the yeathering residual is subject to a ,-- .* 1 moist (at least seasonally) environment in which chemical weathering is very effective. Exposure at the surface will eliminate this moist environ- . A A - --- ment and chemical weath&ing pycesses will be arrested on: the baie ro-ck . % n surface. Crystalline rocks have a negligible porosity, 'and rainwaters will quickly flow off the rock masses. Only where water coylects in depressions or in areas' where a-relatively moist environment ,is ,gres&t, will chemical weathering be active. Sheet wash or channelized flow may be locally effective. The general effect of subaerial weathering will be to spl5ctively P +a --A ------alter the landforms prbducing a variety of distinctive features. her the distinctly arid (arid'in terms of water present on the roclc surface) sub- > 9 -aerial micro-climate pervasive decomposition will be arrested and the basic + forms will persist for long periods. i Domes were found to be almost entirely stable under the arid Australian climate by Mabbutt (1961) who determined no substantial differ- ences existed between domes. currently being exhumed and .those exposed by i , * much earlier erosional forces. Similar observations on the 'retarded decay - sr, . . r'--' of bedrock exposed at the surface are contained in Thomas (19651, " Wahrhaf tig (1965) 'and .&any others. The main subaerial evolution of domes proqeeds by continued dilation of existing and potential jointing as - % 2 developed in the preceeding'section. Subaerial surface wash, parzrcularly 1'. where exploiting _l"ointiplenes,is regarded as an important cmsio agent by Blank (19511, Mabbutt (1901), Thornas (1965, 19661, Leigh (1968) and Jeje (1973). Blank (1951) regarded surface waters as important in loosening viewed as having 2 ccrrrosive, rather than corrasivr: effect as incised e channels have projecting qu9rJz and picrocline grains. Other effects of p .- jointing are as zones of weakness along which weathering depressions can devclopt orbin in and T-.;idale1964), as crevices where debris can concentrate I and boil and vegetation be established (~homa31967); and as planes along $ -"" - + - -- - which chemical weathering can be effective in a more qoist micro-climate. 1 J In Surinam, Bakker (1960) found the surface temperatures of bare 5 granite to reach 7Qk.0 Although insolation weathering has been dismissed -22s a poten; weathering mechanism &research by Blacliwelder (1933) and @- Griggs (19363, more recent work has proposed a limited effectiveness of /. , thermal expansion ahd contraction. Ollier (1960) cites convincing evidence I ------of rock cleavfig due to-insblayion treathering in ~istralia, Leigh ( 1968) regards it as a mechanism behind flaking, granular disintegration-and rock blisters. He notes mineralshave different coefficients of expansion and - - that granite$ generally contain crystals of different sizes. Stress due to those factors could result in failure over a long period in a manner P- analogou%+-.to metal fatigue. Although spectacular examples of cleaved balocks A 'are probably due to the spontaneous opening of latent jointing (Ollier 19651, insolation weathering may be an effective process (or work in conjunction with other processes) on a smaller scale. - Granular disintegration is regardcd as the dominant weathering pro- cess on domes by lJfiite (1945) and Blank (1951). Twidale (1962)-.sees it as important on,xoarse-textured granites,and responsible for their more advanced < -.~- disintegration when compared with domes of finer grained rock. The pro- 4 2e cess is particularly effective where the rock has undergone pre-weathering -- such that the grains are no longcr tied together (0llier 1965). Flaking is a process in which rock j~alesup to $inch thick are shed - -- - " from the bare rqck surface, Ollicr (1965) regards flakding to be a strictly 'i. ------2- subaerial process attacking thc entire rock surface, maintaining its form -- ;@. while causing a small pcdind't to develope around the rock base. The role of flaking on cavernous surfaces was stressed by Dragovich (1969). The ' flakes had their origin hydration along-- fracturki by *. mois ture-Fracture planes developing at the boundary;. of innermost -,.moisture I' penetration resulted in the scales. ~lalcingwas restricted to cavernous areas where temperature and humidity fluctuations were minimized while 2' extreme temperature variation',was regarded as favoring granular disin- , n tegration. a> -A& Indurated crusts are of $en "found on the outer skins of weathering ------residuals. They characteristically are red to orange in color due to the -'. . ? I presence of iron oxides. This probable recementation of the outermost surface of the rock is in many cases responsible for the resistance of the rock to subaerial weathering agencies, particularly when the rock has , previously undergone substantial subsurface decomposition. Anderson (1931) : attributed t+e veneers to capillary action of water drawing solutle salts from the rock interior and depositing them at the rock surface.when the sol evaporates. This process has been termed Itcase hardeningtf as the induration is entirely surficial. Ollier (1965) states the chemical migration may t occur in the subsurface and cites cases of case-hardened boulders found below the ground level. A chemical analysis of an indurated veneer and the underlying surface in White (1944) suggests that the cementation is due to a slight increase in iron and clacium in the indurated zone while other cations shoired a decrease. This is strikingly similar to the elemental migration and banding described by Augustithis and Ottemann (1966),suggcsting that tndurated crusts, p~rticdarly-wfTeremore-tharrone~s~pr~sen~~~~~~~~~~~~ a' ,t~ (Cunningham 19691, are due to a Other, mere superficial 4- induration on the Mojave Desert was described as desert varnish and Sharp 1958). The subaerial resistance of features is perhaps best depicted by thesS-' -- evolution of tor groups in Nigeria by Thomas (1965). The tors comprise * highly resistant landforms at the surface,but are subject- to undermining ?9 from below by contihued subsurface chemical actiop, resulting in their" -2 detachmeAt from bedrock and subsequent collapse*- If a weathering residual *>: becomes~~coveredby a soil layer or vegetation, comparatively* rapid destruc- tion of the features occur in the moist soil layer. The resistance to ?& E subaerial only occurs when the feature is a bare rockklZKdTEi?ip /. with a zesultant arid micro-climate. e The selectivity of subaerial attack is best illustrated by small scale depressions on the surface of tors and domes called weathering pits, panholes or gnamma. These depressions have an azonal distribution on a variety of roclc types and range from small depressions a few inches deep and - % - .? less than six inches across,to large holes fifty or more feet across and rC over ten feep deep, the larger features being situated along joint planes. "A Despite the disparity in size they,+re commonly attribyted to the same -,- r < k v professes. Descriptions of some distincti-ve forms and jwecialized terms are *I . , P contained in Cunningham (l964), Corbin and Twidale C1964), Demek cl9651, ."+'- -w Hedges (1969) and Ollier (1969). A list of the proposed o'rigins kould include the following mechanisms, Matthes (1930 regarded weather pits as forming where aggregates of readily soluble minerals were present in the granite, while Anderson (1931) proposed their origin in the breaching of an indurated veneer by rainwater, r -- -- 9 ---- followed by accelerated weathering beneath the case-hardengd end, r- - Spalling was thought by Smith (1941) to initiate3mathering-. pits, followed by differential weathering due to the accumulation of water and organic natcrizl in them. Vhite (19.44) reported moss growth to be instrumental in breashing an indur~tedvcncer and initiating the depressions. Small scale . - ".-:+f& extension. jointing was thou~hrto be a s&ifi~ant~torbvaanlc(1951) F. I .. d in initiating weatheri?g depressions, and he rdorted some with annu1ar"rims . ("rock doughnuts") whose origin was very obscure lank 1951b). Panholes on a gritstone in th~-? Pennines were attributed to chemical action and swirlingA- water by palme; .and Radley ( 1961). .-< b Corbin and Twidale (1964) investigated a variety of features on ..+ T ~ustralianinselbergs and found them to be caused by differential weathering L ------42 of joint intersections, codcentrations of minerals susceptible to weathering, and the collapse of rock blksrers.;/' Morphological detail was described and 1 &ccounted for in thcs exhaustive report. 3edepressions occasionally reached an immense size and were the centers of centripetal drainage on the P , dome. In arid areas of Australia, they comprise an. important water source, . retaining sibstantial amounts of water well into the dry season. Rock tanks*12,ft across and 8 ft deep were described by Hilton (1966) as being , ,+f < initiated by exfoliation and enlargened by chemidal weathering. Roof lakes* -- s on Nigerian inselbergs reported by ~~acd~~'(1960) are interesting in that r - z$. + they served-as-a water souz6e in times of siege for villagers on fortified inselbergs. Shallow depressions of great size reported by LeGrand (1952) ' and Reed (1963) were attribute$ to solution. Dahl (1966) described weathering pits in a periglacial area as being due to microgelivation and chemical weathering. Wezthering pits have also been investigated by Tschang (1962) arid Bakker (1960). Demek (1964a, 1965) regarded chemical holTo~isin~feT&sp~~s,~~iEh~wOurthcnbe~~- -- action as causing .. microscopFc f racturcd '&y 'free-tr=thzw artion, giving ris&;ko weathering pits. Development would be by combined physical, chemical and biologic processes. I.7eathering pits are commonly developed on a variety of crystalline or massively bedded sedimentary rocks. They seem to be absent only from highly foliated schists, although Hood c1951) reportssurfac~cavities,flutines~- If and hollows that arc apparently subaerial forms. Rapid formation of -6 weathering pits is reported by Dem"e1c (1964b) and Dahl (1966). In general,' 6 although rapidly developing features in geologic terns, veatherinrg pits t - do not noticably enlarge over historical per7iods and in many cases it is " 4 difficult to determine whether they are developing undcr contemporary conditions. Cunningham (1965) used- weathering pits as an -index of'whether ------ a tor was intact or had been decapitated by glaci'ation.' Although definitely subaerial forms, it is unlikely that they can be used as a dating index as E they form under an extreme climatic range (tropical-de~eft-periglacial) and *+- by diverse processes; being an excellent example of the process of con- a vergence. Another microform consisting of n-arrow rilling or gutter forms - I occasionally occur on tors and inselbergf and are called psuedokarren; lapies, or granitrillen. Lin (1961, 1962) and Twidale (1971) attributed / them to the mechanical action of rainwash on steep rock surfaces,while Wall 3 2nd Willford (1962) regard the solvent action of rainwater as the principal ..* -./ ,z<" process responsible for the form. Demek (1964b) cites the a&& of both chemical a~dmechanical attach by rainwater. Flutings and crenel ations on the Pennine tors were regarded by Cunningham (1964, 1965) as paleoforms of I* Tertiary genesis. He distinguished between true lapies and the overflow a gutters of panhol es. While interesting micro-forms, their limited"occurrencc ------suggests they are not a ubiquitous weathering phenomena on weathering The peripheral areas of domes and bornhardts have received considerable 0 attention in the literature. Run off from the domes concentrates in these * - .P areas which may havG a more abundant vcgetal cover or be explo!7kd as a ar+und the margins of inselbergs have been investigated by Clayton (1956), % Didknoiiski (l96O), Mabbutt (l965), Pugh ( 6 ~hom& (1966) and Peel (1966). The depressions have been attributed to localized removal of material in these areas by stream erosion, eolian action or volume loss I. attepdant u'pon weathering (Ruxton 1958). These depressions are a special . " case- of a more general phenomena, the abrupt change of sl~p_cazuixne-moxes- <. from the general topographic surface on to the inselberg. This is common,ly 2 called the piedmont angle. .$< 'L - The origin of the piedmont Agle has+aroused the curiwity of many . ,*: writers. Traditional theories of pediment-$&?mation ascribe it toasorne - .<#< combination :of -bacl:vrdaring, shekt wash or lateral stream erosion at the pediment-inselberg junction. A satisfactory presentation of these early ' It theories is contained in Thornb,ury (1969).rJsome adherence to these theories ... ' continues to present times. Rahn (1966) eccepts, for example, stream erosion as the priqcipal cause of the piedmont angle.. Other recent accounts have stressedc, however, the role of subsurface weathering in the kvolution of I- . f- the angle. Ruxton (195C) envisioned the piedmont angle as resulting from accelerated chemical rreathering and subsurface ,flushing at the inselberg foot. The sudden change in mobility i.n debris as corestones and boulders , disintegrate into griis is cited as the origin of the sl6pe break. These s finer materials ~rouldbe concentrated by erosion,allowin~an incipient slope ------break to develop.. The differential weathering in the moist marginal areas is regardcd by Twidnle ( 1962, 1967) to produce conc$'pities by basilp sapping "of the inselbcrg. Subse-,uent.lowering of the general surface by erosion c'1 exposes rliese concavities, creating the piedmont angle. A lithologic change 2 in sedimentaries is also regarded as an Fmportant factor in the formation of some piedmont angles (Twidale 1967). r Thomas (1965) viewed the sharp slope break between bornhardi and topographic surface to be dye to a combination of .erosional downwearing in*, ,-. + 4 a deeply weathered 'landscape, and the delineatipn of the bornhardt by vertical and domical jointing, both factors working to produce a sharp piedmont angle: Mabbutt (1966) and Oberlander (2972) regard the piedmont .* angle as being formed beneath a deep weathering mantle on Tertiary hills, ------with subsequent stripping of the mantle exposing the bedrock surfaces and piedmont angle. Pediments would be a cembination of etchplains evolving I by down and beckwearing of the hill by deep weathering. ~abbutt(1966) sees current evolutisn by subsurface notching at the piedmont angle and sub- surface weathering of the pediments. These positions are also presented by Twidale (1962, 1967). These theories probably again reflect a land- scape feature due to convergence,and may be accepted as reasonable explan- ations of an interesting morphological feature of inselberg landscapes. . - Glaciation I In some areas both angular and rounded tors have been found, the Ad- F. ;angular tors are thought to have resulted from a one-stage periglacial morphogenesis while the rounded tors are ascribed to a two-stage or-&in .. . " (Demek 1964, Caine 1967, Czudek and Demek 1971, Kaitanen 1969). The same tor groups have been described by different writers as primarily angular and or as rounded or of a ho-stage origin in ton 1-955, 1964, Cunningham 1965, - Eden and Grecn 1971). Other instances of tors ifi the same area but due to . PI different processes arc contained in Dcrbyshire (1972) and Ward (1969). ~llj., of these instances -arc concerncd with relationship of tors and glaciation. 7 ------ A r %-urring theme in the literature is that where both r and angular tors are found, the angular tors are found on side slopes-- while the rounded tors occur in summit areas. These have usually been interpreted I -as reflecting two different modes of genesis, the angular tors being the resdt.of periglacjal processes and the rounded tors relict landfops of a < tv;o-stage morphogenesis (~emelc1964a,b, Caine 1967, Czudek and Demek 1971). Demek and ~ainereached similar conclusions about the origin of slope and - - - - summit tors. Demek (1964) linked the pre-PJeistocene tors to zones of relict weathering profiles located at the foot oG or near tors and kcipjks. . . The general assocaition of form with evolut?on'~lscomplicated by the dra- natic changes of climate which occurred in the Pleistocepe. Czudek and a Demek (1971) wte: As well as tors created by cryogenic processes other&ors, developed in the Plioc,ene by exhumation from kaolinitfc regoliths, appear, to have been remodelgd by~periglacialconditions, especially in granite are* (~zudekand Demek 1971 pg 105). The tors have in some cases been completely altered by the periglacial processes and are indistinguishable from true periglacial tors (by form), Identification in such cases is difficult in theaabsence of a preserved -* '6s regol4?'th or other indicator of deep weathering. "~n~ularizationof rounded tors is also noted in Caine (1967) and Derbyshire (1972). Derbyshire (1972) stated that the hillside tors are due to periglacial frost action, while the rounded summit tors are due to subaerial chemical . % < -5 a - I. action fn the Pleistocene (in Antractica this dates from 2.5 m.y. to the .,. - -- t ~resent). The chemical alteration on the summit tors (diabase) consists .- ~f weathering penetration along cleavage -$anes, fractures and crystal I boundaries to a depth of 2 inches,with concomitant clay formation;' The -. chemical weathcrikg is restricted to the xeric ridgetop as frost shgftering i dominates on the more moist- side slopes. A two-stage. m&phogenesis is 7 -5 *6 rejected because of the topvraphic posi Co $and absence of a weathered 52%C +4 . - regolith. ,? ,. - * ~erb~shire(1972) is the only &%ter proposing, the origin of rounded / * tors by chemical weathering under a periglacial environment. There is some question yhetBery chemical weathering-is sufficiently active in the=area to r< - '* , ' r produce the -forms. Chemical weathering is ~inext;icahJy linked-tie., t&e 7 - -- - presence of water and is generally arrested under xe~icconditions. Kelly - * n and Zurnberge (1961) concluded thqt esfintially no chemical alteration was . = present on a _quartz diorite in BcMurdo Sound, Antarctica and was almost entirely arrested on bare rock surfaces. In a seasonally moist soil -" -, kvironment in the arctic, Hill and 'TedP6w (1961) foyd the fine fraction of 4. the soil to have been produced by micrcgelivation and differential expansion of minerals. Evidence of solution, oxidation and hydration was present 3 while hydrolysis was limited to cleavage 'surfaces and crystal boundaries, 3 - - v Antarctic pedological investigaHons cited by Derbyshire (1972) show a 4 similar lack of alteration. Czeppe- (1964) described a case of apparent exfolYation resulting from the weathering of a sandstone in the arctic. . These investigations show that chemical weathering probably is very limited even in moist environments. Weathering in t,he xeric conditison of a nunatak r ridge in Antarctica is probably entirely arrested, or at least incapable - P of producing tors as suggested by Derbyshire. No mechanism is proposed for i -- the initial iso'lktiort of- the tor bloek, and ~&erne~ka&aLl1t+~st'show----- some angular frost shattered faces and some show freshly shatrered fatlesIt (~erbyshire1972 pg 100) suggeststt$! conLernporary subaerial attack is converting all rounded forms t.0-angular faces. The xeric condition of the -2 summit area would be the tors rather than causing them to evolve. ,r' ------*- A- L - - - The reasons given for the rejection of a two-stage morphogenesis are poor, - -- a 3 the absence -of a regolith does not prove it never existed, and fhe topo- graphic positiorr is identical to that of two-stage tors describe2 by Dernek (1964) and Caine (1967). While the evolution of the tors is uncerkain,the *. '. hypothesis presented by Derbyshire (1972) is implausible. No periglacial process capable of producing spheroid or rounded forms has yet been sub- * + . * F . . stantiated. . I ------I - v- Schisc tors of ~e%Zeland are of both a periglacial and deep weathering origin. T.cartiary tors are found at lower elevations (Raeside 1949, Ward 3 1952, Turner 1952, McCraw 1965) in varying stages of exhumation. P-&& glacial tors are described by Wood (1969) who argues that cryoplanati&n was extremely vigorous, destroying the Tertiary weathering landscape and ' - insBituting a completely new landscape. The natur~e-ofthe schist bedrock results in the tors having $*similar appearan&. - Tors demanding a poly- +. -*' genetic .origin ....-. were found inzLapland by Kaitanen (1969) who again made a 9' q, -9. *- a genetic &@$inction of the basis of form. Through most of the Pleistocene, -+ -. '" '% these tors had.been submerged beneath a continental ice sheet which is d regarded as having protected the forms from periglacial frost shatter. he relationship of glaciation and tors was, however,.. a topic of controversy = '- > ... - -in earlier literature. y.- Linton (1955, 1964) postulated that tors were too fragile to survive active ice action and propo-sed their use as indicators of nunatak areas "fragility" of tors were taken by ~almer(l956),~almerand Radley (1961)- and- *" Palmer and Nielson f 1962). The two-stage rnorphose~esis of the ~&tmoor Tors a i in ton 1955) was rejected by Palmer and Nielson (1962) due to the limited weatllering of the griis, th; presence of hydrothermal clays in the area and :# ..J % to the fo& and distribution of thetors.' Proposi~g~ubaerialrounding of?* . :, ' 3'. angular Pleistocene features in recent times; theyestat@a major problem; , d in +the interpre'tation of tors: -v It might be asked whether the dominance of angular tor shapes is . I primary or secondary, ' that is, we would like to'know if the preliminary tor-shap'c'was angdar, the prddkt of frost action 'and " '7 subsequently softened by granular disintegration, or whether it ' was basically rounded, produced underground, and subsequently sharpened by frost action after exposure (Palmer and Nielson 1.962 c pg 328). , . + A ------ 4 Although the olijections to Linton's hypothesig posed by Palmer and *~ielson " .". are salient points not covered in Lintbn's inquiry, later work by Eden ind , = anh Green (1971) 6istinguisi1ed between the gGs hydrothermal prodects.an&" .$ accepted a two-stage evolution, although significantly revising,Lintonts < Another tor group of disputed origin, the Pennine tors, were regarded as periglacial tor's by Palmer and Radley (1961). The area had-been unglaciated during the final Pleistocene ice advance and the tors were -" - * cm interpreted as dating from that period. Linton* questioned U - glaciation had occurred in the area. Citing the rounded fork of the tors, remnant of a regolith, and -weatheEng penetration on joint surfaces, he proposed a two-stage genesis. The area was reinterpreted by Cunningham (1965) who stated that the tors had survived glaciat-ion, although many had been dis- 1- placed from their original position by advancing ice. Although originally s of a two-stage origin, the tors were interpreted as having undergone sub- 9 stantiaf subaerial m6ddrfZcation. ThispCtUhy, Fn denyi~t~c~%CF??f-~@o~~--- t as irtdirators of mtgf*ciaced areas, mrtccd the brginrring of a Tien inter- pretation of tl~erelationship of tors and glaciation. Another apparent case * of tors surviving glaciation was found in. Tasmania by Chine (1967). Pheasant and Andrcws (1973) and Boycr and Pheasant (1974)reprtcd tors on-upland and 'E i , . ------2 I+ 1 smit areas of Baffin Lsdand. The to= are regarded as occurring inwareas - - - A '+ not glaciated or not covered with actively moving ice in the Pleistocene, j. / and are interprete4a.s >. remnants of Tertiary weathering profiles. I .,. I r The relationship -of..t&-s, rwoliths and glaciation took on new kx .i dimension yith the work70f sugden (1965) in Scotland, where-he fo&d a ' strikin$ juxtaposition of glacial troughs, periglacial landf oms abd tors in a summit area thnt had been submerged beneath a Pleistocene ice t'sheet. 2 ------The great variety of landforms were interpreted as reflecting not the presence'ofJ, the ice sheet,.bu.t variable action within it. The survival of the tors uas attributed to the selectivity of erosion due to channel- b * r ization of flow within the ice sheet. Similar channelization of flow was demonstrated by Clayton (1965) in New York. He'cites gtudies of ice flow, ice caps and sVggests that channelized fl& ) ,O 'S 4 in ice sheets. T* ' d Kaitanen (1969) postulated that the ~liestoceneice sheet in La.pland ' . ' t - - had $reser,ved tors, end cited evidence that only low intensity erosf'on had Seen done by the ice. He furthcr notes that "the composition of the till is really rather an exact ref1 ection of the earlier weathering crust" (~aitanen1959 pg 53), and cites one case in which an intact regolith and, till have a similar conposition. The advanced rounding and chemical de- i d- 6 caiposition of boulders in CBnadian tills was regarded by ~rochu'(1959) ,_ ,- - "-- - - 1 as evidence that they were not weatltercd in 'situ but were decomposed duringY 1 a lung per Fod of Teqtiary weathering similar to tke-dccp wcathezhg-found ir. Brnzil and Guyznn todny. In both tllesc cascs the oriiin of till/. was--- th~ugiitto de the result of the erosion of a pre-weather&d mantle by the I action of continentcl ice sheets, and little evidence of substantial erosion .rd 3- - 1 -4 Y of frcsh rock was found. ,& ------'.3 '.3 hv These sources establish the ability of tors to survive submergencc - - - beneath continenpa ice sheets, The original theory that tors would be 2 , -destroyed under these conditions probably =resulted from an erroneous ul , ' assymption that the erosive power of ice sh~etswas comparable to that of _. - r, valley glaciers. The ideas expre-ssed above and the importance of deep . +"a wea;hering in the evaldation of mid-latitude landscapes were greatly * ' extended by the work of Feininger (1971). Limiting the erosive power of F : - ice sheets to the removal of pre-weathered mantkes, Fei~ngerci2edi-rrstaitc~s------L 9. of undisputable pre-Pleistocene weathering progiles in Eastern Canada and 'i the northeastern U.S.A. He'compared thc contemporary,shield topography -& ' and deranged drainage of eastern Canada tw the weathering front topography P developed from multiple borings through a regolith in Colombia. Similar = % 4.. - positions have hpm aap~tedin other areas by other writers. Kaitanen (19e) reg9rd regarded by Gjessing (1967) as the product of deep weathering and subaerial slope processes, &ting from a proposed Tertiary peneplain. Contemporary hills were thought to be unweathered rock cores still partially enveloped by remnants of a weathered mantle, y valleys and fjords were though,ty, .plaf to be forms developed in zones of closely jointed and deeply weathered -- )L bedrock. Caine (1967)vthought some of. fhe m&nill&tcd surfaces of the 8 - E Tasmanian Plateau :.:ere exposed weathering fronts rather than glacial - - ' W features. r; C I The tectonic stability, crystalline bedrock, and warmer climates of The northern portions of both theea-and western hemispheres indicdte th2 a radically different- morphogcnetic regime and LBndscape may have been present, and specifi_eally, that deep weathering may have been a common ., ------e-- - P -- process over large areas irhqch today are domin'atcd by other kinds of weather- i ' -- &.. ".t, =ing processes. Despite the lidown occurrence of repeated continental 9 glaciation: .. .patches of preglacial weathered ro&' mantle are so widely distributed-that it becomes difficult, if not impossible, to deny the former presence of a uniyersal weathered rock mantle of apprecXiable thickness in these areas, and by inference elsewhere in the northern hexisphere (~eininger1971 pg 661, This conclusion is directly opposed by 1 (1972) who argues (I - - -- on the basis of indirect evideneE) that the great bedrock exposur e 4 Precambrian shield areas of ~orthAmerica and Scand~naviaare the of deep erosion by continental ice. A major problem is that both deep weathering patterns and ice sheet erosion are influenced by similar structural controls (jointing and petrologic susceptibility to weathering), making it S difficult to separzte ttle effect of:.the two proce'sses when they have worked in the same aree. Although the hypothesis postulated'by Sugden (19681, Gjessinn (19671, ~aitanen-439691,~cinin~er (19711, and many others must J be subjected to field testing, it is probable that a landscape type . . . 2nd process now only in tropical areas will be shown to have been of far greater range in the past and responsible for more contemporary -**w -t .+ lzndscapes than is coiruxonly accepted. ,% Dating The precise dating of pa2eo-landforms is not generally possible as they scldoz occur in conjunction ~.rit11fossils a sedimentary stra_ta, lava -- -* , *---< flo::s or other datriblc c./ents. This is p'2trticularly true in the case oT ------ landf or~~presuzcd io $27:~ their origin ;&der palco-weathering conditions, Angulnr tors of peri~lecial~or~h6~encsis have an obvious origin during the Plcistoccne and in 0.Tzses are continuing to form under present conditions (Dernek 1964a,b, &&ek 19W, Caine 1967,-Martini 1969, Wood 196?).. It has % not'prgven possible to date these features in te3ms of specific advances "- /"' , and =.I%r&t_eats of glacial ice. Tors occurring in areas in which deep I' ,*+ \ " weathering is not currently a dominant process are generally regardpd as Tertiary landforms, although the dating is tenuous in most cases. The dating of weathering residuals generally rests on interpretations i,' ec: of peneplanation surfaces,-- tectonic events, or erosional and weatheririg ------cycles. Landforms in Africa-are interpreted as polycyclic features; continuing to form under contemporary conditions but 'having their originfL*. *? early in the Tertiary or possibly the Cretaceous (~homas1965, ~chrder1973).- * Feaures'in Australia are similarly regarded as Early Tertiary or possibly ',L 4 Cretaceous landforms (~abbutt1961). The tor' and bornhardt landscapeUof Wyoming has been dstpd the rnciticn sf the landforms in relation to evkdence 9. of inferred sequences of uplift and denudation dating from the Tertiary (cunningham 1969). Eggler et a1 argue that the parkland-tor and planar Sherman topography of this part 02 Kyoming are "naturally qoexisting , ,* topographic facies" (~ggleret a1 1969 pg 521.) due to lithologic control, and state that the different topographies would occur whenever the area is tectonically stable and mrundergoing dissection. The present landscape is regarded- as dating back to the Tertiary (agreeing with Cunningham 19691,and , . at they postulate the topography would have also been present during the Pennsylvanian and Precambrian, While the structural control proposed cIoabtIcss exists, the interpretation of tXe TaTCs-~apeX~'2opOgraph1T--~ 9 J facies" is unrcasonzH& The genesis and exposure of the landscape must be attributed to dynar,lic processes and changes of process rather than a static 1irhologic factor. The limited abso&ute dating of tors and rcgoliths supports the g-a1 . -4-v hypothesis that these are Tertiary landformsl Obcrlander (1972) radio- i metrically dated a lava floybovc a regolith which was contiguous to a boulder-mantled slope, establishing that the deep weathering responsible fox - + i the landfofk is at least of Pl~oceneage. The schist tors of New Zcaland are being exposed in places,as Miocene sediments are being strippe away, and must antedzte.the Miocene (~aeside1949). Tor topography in New South ------ Wales, Australia is being exhumed from beneath an Oligocene basalt (~ro~me 1964);,, and the tbrs examined in British Columbia as a part of this thesis had been buried by Eocene volcanics and sediments which have been dated in nearby areas as Middle Eocene ( 50 m.y.1. These tors constitute the oldest weath,ering residuals which have been given an absolute date, although some tropical landforms are probably nore.ancient. Far older are corestones and ,- a deep weat'ncr:r,, profile invptigated by ilahlstrom (194G) ,in Colorado which lie beneath a Pennsylvanian sandstone. A recent discussion about the problem - of dating tors has been the subject of a paper' by Cunningham (1975, "Tors as C- indicators of Palaeo-climatest'-Paper- read to Brazilian Academy of Sciencc, -$7 F at Porto Alegye, Brazil). In conclusion, although the origin of weathering residuals may .be assumed to be during the Tertiary (~articularl~in mid-lati- > tudes), inferences as to the type of climate and time-of exhumation must be &. , based on other evidence. -- - d' Z ' _'- - Analysis of Cathedral Park Tors Morphogenesis An analysis of the tors located on McKeen Ridge must begin with an assessment of the age of the landform as this factor is of pre-eminent importance in the establishment of the morphogenetic regime under which they evolved. Both a probable maximum and a rather precise minimum age of the tors can be achieved by examination of the geologic history of the area (developed in an earlier section of this thesis) with respect to the tors. The tors are features developed exclusively on the quartz monzonite bedrock of the Cathedral body. This granitic pluton was first described by Daly (1912),and is one of a number of Jurassic plutons in the Princeton map-area investigated by Rice (1947). An intrusion regarded by Rice (1947) as synchronous with the Cathedral body has been radio-metrically dated at 156 m.y. (~oddicket a1 1972). Pendant material of the Nicola group (~riassicvolcanics) present at the north end of the study area,and Permian sediments near the Park entrance indicate the tors are formed in the outer portion of the pluton, and suggest that the tors developed soon after the quartz monzonite was unroofed in the early part of the Tertiary. The sharp contact of the plutons with the Triassic rock indicated the granitic rock had its origin by magmatic injection, rather than a grani- tization process. There was no veidence of strong interaction of the upper portion of the pluton with the overlying rock (no hydrothermal alteration or other non-meteoric rock) and no indication that the tor forms were part of the original relief of the pluton. The sharp contacts and absence of hydrothermal alteration or other interaction of the pluton with the country rock indicate that the granitic melt had a temperature lower than the melting point of the dominant minerals of the lava, preventing intermixing of the magma with the country rock and restricting contact metamorphism in the Nicola andesite to a partial remelting of portions in close proximity with the magma. Although the Princeton map-area is rich in ores of hydro- thermal origin ice 1947),no ore deposits or other indication of hydro- thermal solutions are found in the Park area. The small size of the tors makes it unlikely that they are "cupolattforms inherited from the relief of the outer portion of the pluton,and the absence of hydrothermal or other non-meteoric alteration indicates that their morphogenesis has not occurred in a part of the pluton weakened by interaction of the granitic melt with the overlying rock. Tors elsewhere, however, have been shown to have resulted from these two conditions (cunningham 1971). Although no Jurassic or Cretaceous sediments are present in the Park, they cover much of the area to the north c ice 1947),and sediments of this age are thought to have been deposited in a narrow sea which covered the present day Bark and surrounding area (~udkin1969). There is no indication that the g~aniticplutons were injected into Jurassic material. The deposition became deltaic and continental early in the Cretaceous and was halted by a major mid-Cretaceous orogeny (~c~aggart1970). Erosion accom- panying and following this orogeny resulted in removal of the sedimentary overburden andifirst exposed the quartz monzonite to meteoric weathering. This period of denudation is thought by Willis (1903) and Holland (1964) to have produced a low relief surface (peneplain) which was present in the area during the Paleogene. The tors are, therefore, unlikely to antedate the Tertiary. A more precise estimate of the minimum age of the tors can be made. Tors are being exhumed at the northern boundary of the study area from beneath volcanic and sedimentary members of the Princeton group. These sediments are also found in a joint-bounded cleft in the quartz monzinite 314 mile south of the Princeton group-quartz monzonite contact near Giant's Cleft. The Princeton group stratigraphically overlies and is younger than the tors. Rouse and Mathews (1961) and Hills and Baadsgaard (1967) radio- metrically determined the age of the Princeton group at 50 m.y. (~iddle Eocene). The tors of McKeen Ridge are relict paleo-landforms which predate the Middle Eocene and probably are no older than the beginning of the Tertiary. Their genesis presumably occurred under the geomorphic regime during the interval between the unroofing of the pluton at the beginning of the Tertiary and burial of the tors during the Eocene, A broad assessment of the geomorphic regime of the Park and contiguous areas during the Paleogene can be made, thereby allowing an assessment of the probable morphogenetic,regimeunder which the tors evolved. The paleoclimate of the area during the Eocene has been inferred from fossil evidence contained in the Princeton sediments by Bell (1947) and Hills (1962). Their conclusions were discussed in an earlier section of this thesis. In summary, the Eocene climate was warmer and more equable than the con- temporary climate of the British Columbia southern interior,and was drama- tically different from the alpine climate now found on McKeen Ridge. Although abundant precipitation is thought to have been present ell 1947), the climate is not regarded as having been truly subtropical. The presence of a peneplain surface in the Paleogene (Holland 1964) makes it impr/obable that aggressive surface (fluvial) erosion was present. The combination of a moist, warm climate and low intensity surface erosion provides the essen- tial conditions for the development of a thick regolith of weathered rock (Strakhov 1967) as subsurface chemical decomposition then produces weathered debris faster than their removal by erosional processes. Deep weathering regoliths are present today on the Atlantic piedmont of the U.S.A. (~eithand Craig 1965, Harriss and Adams 1966) and deep weathering is regarded as an important process in the evolution of inselbergs in the same region by Kessel (1974). The evolution of tors at the base of a regolith is consis- tent with many theories concerned with their origin i in ton 1955, Ollier 1960, Mabbutt 1961, Thomas 1965 and many others) and is supported by petro- logic and morphologic evidence from the tors themselves. Before discussing this evidence it should be emphasized that the morphogenesis of the tors did not occur under Pleistocene or recent conditions (i.e., they are not the product of a one-stage morphogenesis), and, although a two-stage deep weathering morphogenesis is proposed, this weathering was not effected under tropical conditions, and a tropical environment is neither regarded as necessary to explain the occurrence of deep weathering nor would such a position be supported by fossil indicators of the paleoclimate at the time the tors were formed. In the explanation of certain North American deep weathering profiles and associated feature, Dury (1971) proposed the extension of tropical conditions to mid-latitude areas. This association of climate and weathering is rejected in the origin of the tors examined in this thesis and evidence regarding the origin of these tors in no way supports Duryls contention. The most striking evidence that the tors were isolated by subsurface chemical weathering is the incoherent state of the tor rock. The quartz monzonite, although not pervasively decomposed, has undergone sufficient alteration such that it is readily broken apart by hand, retaining little of the mechanical strength of the fresh bedrock. Microscopic examination of weathered samples showed only biotite to be significantly altered. In an earlier discussion accessory biotite was shown to be more susceptible to weathering than other cormon constituent minerals of granitic rocks (Goldich 1938, Keller 1954, Nossin and Levelt 1967 and others),and examples were cited in which the alteration of biotite to clay and other secondary minerals was regarded as producing stress within the rock, leading to its mechanical disaggregation after limited weathering (stephen 1952, Dumanowski 1969, Wahrhaftig 1965, Eggler et a1 1969, Clayton 1974). The alteration occurred in a subsurface environment and coarse-grained granitic rocks were part- icularly susceptible to this type of weathering attack. The friable, weathered state of the quartz monzonite in the tor area (see photograph 11) is the result of the type of weathering attack outlined Photograph 11.-Decomposed quartz monzonite and griis on McKeen Ridge. above. It is unlikely that the weathering occurred under subaerial conditions. There is a general consensus that subaerial exposures of crystalline bed- rock in areas other than the humid tropics are largely immune to chemical weathering (~homas1965, Wahrhaftig 1965). The disaggregation of granitic rock by stress resulting from the weathering alteration of accessory biotite to clay minerals often porduces a residual material consisting of disaggre- gated crystals of the parent material, a material known as griis (wahrhaftig 1965, Eggler et a1 1969, Oberlander 1972). A grzs layer is present today between tors on McKeen Ridge, and single quartz and feldspar crystals from the quartz monzonite are found in the Princeton sediment, conclusively establishing the existence of griis and,by inference,a regolith of disaggre- gated bedrock prior to the deposition of the sediment in the Eocene. Although no complete section of this proposed regolith is preserved, substantial areas of poorly coherent bedrock are present, particularly be- tween tors. The absence of unconsolidated portions of the original regolith is puzzling as it might be anticipated that it would be preserved beneath the Princeton group at the contact of the Princeton group and Cathedral body. The Princeton sediment does not come into contact with an intact weathering profile anywhere along its contact with the Nicola lava or Lakeview and Cathedral bodies, but rests on fresh or poorly coherent bed- rock. The thickness of the sediment varies greatly, from a minimum of five to ten feet in the saddle west of Pyramid Mountain, to more than 60 ft in an incomplete section southwest of Ladyslipper Lake, and to over 200 ft in the cirque wall west of Quinoscoe Lake. As the sediment is only gently tilted, this variable thickness indicates that the sediment was deposited over an irregular (non-planar) surface. In the tor area the absence of weathering pits on recently exhumed tors indicates that the tors were not subaerial for any length of time during the Eocene (this will be discussed at greater length in the section on weathering pits). The proposed regolith must, therefore, have been removed before the sediment was deposited. Fortunately evidence is available which indicates how this may have occurred. Examination of the relief of the Lakeview body and Nicola basalt along their contact with the Princeton sediment, as well as the relief of the tor area which had been covered by the sediment, suggests a number of low hills and ridges were present during the Early Tertiary, The present strike and dip of the slope of the tor area on the west side of McKeen Ridge are N 420 W and 150 W, while values: for the slope between the ridge summit and tors isolated south of Ladyslipper Lake are N 400 W and 7 0 E. The sediment strikes N"15'~ dipping OW. Returning the sediment to the hori- zontal changes the slope orientations to N 60•‹w dipping 9'~ and N 28'~ 0 dipping 12 E. The Eocene weathering front, as determined from contemporary exposures, of the granitic bedrock, had a plan section of a low ridge, As the sediment lies directly on this surface, the ridge must have been located within a larger valley for impounded waters to cover the form. The reason for the localized impoundment of water at this time is not clear but, because the Princeton sediments are associated with lava flows, it is suggested that damming of a stream occurred as a consequence of either earthquake- induced mass movement, or the crossing and blocking of a valley by a lava flow. The relief of the ridge formed by bedrock tor surface (synonomous with Eocene weathering front) across the field area is a rise of 500 ft over one half mile. The observation that the Princeton sediment rests on intact rock, rather than regolith, necessitates the removal of the regolith by some means before sediment deposition. Two cases may be proposed to account for this sequence. If the weathering front and subsurface ridge-form had been submerged beneath a regolith whose upper surface was a plain (following the model of Linton 1955 or Thomas 1965), damming downstream would have submerged the regolith, preserving considerable sections of it beneath the Princeton sediment. The absence of any preserved regolith makes this theory untenable. A more suitable model includes a topographic surface corresponding to the weathering front, i.e., a ridge whose cross sectional profile is similar to hill profiles of Ruxton and Berry (1957) and Oberlander (19721,with the thickness of the weathered mantle being least on the summit area and pro- gressively thicker on lower slopes. The abrupt termination of the tors on both sides of the ridge reflects the trim lines of Pleistocene valley glaciers. In pre-Pleistocene times it may be reasonably presumed that the tors extended to lower levels and possibly across the valley floor. Down- stream damming and submergence of the ridge may have caused the unconsol- idated regolith materials to slump off the ridge and flow into lower levels of the adjoining valleys. Later deposition of Princeton sediments occurred on the weathering front, i.e., the present day tor-studded surface. The Princeton lavarflow locally protected the tor area from erosion resulting from the minor Miocene la ice 1947) and major Pliocene and Pleistocene (Rice 1947, Holland 1964) orogenies. A schematic presentation of the evolutionary sequence of the tors is contained in figure 9. Notable in the figure is the exhumation of the tors in late Pliocene times after,or shortly before they had reached elevations above the regional tree line. This exhumation is presumed to have resulted from the rejuvenation of surface erosion during this uplift. A factor establishing the indubitable subsurface morphology of the Early Tertiary Post-Eocene Late Pliocene Post-Pleistocene Figure 9.-Schematic portrayal of the morphogenesis of the tors on McKeen Ridge tors (in addition to the previously described weathered state of the bedrock and gr& material present in the Princeton sediment) is the morphology of the tors themselves. Earlier in this thesis a model for a deep weathering profile developed on regularly jointed crystalline bedrock was described (see figure 7). Subsurface weathering by circulating groundwater produced two principal morphological characteristices, an exploitation (etching) of joint surfaces along which water could penetrate,and spheroidal weathering of joint bounded blocks. Subaerial processes were regarded as not being capable of this pan-directional weathering attack. The McKeen Ridge tors (see photographs 5 and 6) are joint bounded, ubo~lderizedl'bedrock blocks,and superincumbent blocks characterized by etching at joint planes and rounding of corners. They are remarkably similar in appearance to other tors discussed in the literature (see in particular Cunningham 1968 pg 195 and photograph 5). Corestones were found within the tor area. In a sidewall of the northern cleft of the Giant's Cleft dome, corestones were present in closely jointed zone beneath the upper rock surface (see photograph 12). A narrow tunnelwascut&ng a joint plane beneath a tor block, and substantial etching of joint planes was present in the same area (see photograph 13). These morphological character- istics indentify the features as tors and demand a subsurface morphogenesis. A one-stage periglacial morphogenesis proposed for angular tors (~emekl964a, b, Czudek 1964, Palmer and Radley 1961, and Palmer and Nielson 1962) cannot explain the rounded forms encountered on McKeen Ridge. Frost shattered material is found on Nicola and Princeton basalts to the north, and on the Lakeview granodiorite and Cathedral quartz monzonite to the south and west, but is. entirely absent from the tor area, The tors are apparently immune to macrogelivation and are evolving slowly by granular disintegration. Photograph 12.-The photograph shows weathering penetra- tion and corestones in the sidewall of of a cleft on Giant's Cleft Dome. The photograph shows a thirty foot section of the sidewall. Photograph 13.-This photograph shows the substantial etching on joint planes on tors in the vicinity of Giant's Cleft Dome. Imme- diately to the right of the hammer is a six foot tunnel cut through the rock. This is not without precedent. Tertiary tors formed from coarse-grained granites were found be Demek (1964a) to be very resistant to periglacial frost action,while tors in fine-grained rockswere substantially remodelled. The ineffectiveness of ma~ro~elivationin the tor area is thought to result from the absence of tightly closed joint planes on tors along which water could penetrate and expand under confined conditions. As has already been noted, joint planes have undergone substantial etching such that tightly- closed joint surfaces are encountered at depths in the rock where the static confining pressure of the rock mass is probably greater than the pressure exerted by volume change of water to ice. The complete lack of frost action is unusual in that in most cases in which tors are found on ridge summits and side slopes the summit tors are rounded in form,while angular or angularized periglacial tors occur on side slopes (~emek1964a,b, Caine 1967, Czudek and Demek 1971, Derbyshire 1972, Pheasant and Andrews 1973). On McKeen Ridge tors on side slopes, like the summit tors, again are apparently evolving only by granular disintegration because of the etching present on joint planes and the weathered condition of the rock, Other theories must also be rejected. Neither the degree of chemical alteration of bedrock in the tor area (over 7 inches of weathered rock is often present before sound rock is reached),nor the distribution of tors can be explained by Dahl's (1966) theory of niicrogelZvation and chemical weathering or Derbyshire's (1972) theory of periglacial chemical weathering under xeric conditions, Hydrothermal or other non-meteoric alteration was a factor intors investigated by Caine (1966), Ford (1967) and Cunningham (1971). The sections of granodiorite below tors exposed in cirques give uncontestable evidence that entirely sound bedrock underlies the tors. Microscopic examination of biotite in fresh samples showed no indication of pre-alteration described by Eggler et a1 (1969). Although the tor area is thought to lie in the upper portion of the pluton, the small size of the tors makes it unlikely that theyare inherited from the emplacement of the pluton in the manner of certain bornhardts investigated by Cunningham (1971). Their distribution has, however, been partially explained in this manner. The McKeen Ridge tors are the products of a complex, two-stage morpho- genesis in which morphological characteristics were developed by subsurface weathering on a low relief surface in the Early Tertiary under temperate, mid-latitude climatic conditions. The low ridge under which the tors formed was submerged beneath a freshwater lake during the Eocene, resulting in the movement of regolith material off of the ridge, exhuming the tors. Sedimentation within the lake ultimately buried the tors, after which basalt lava flows covered the entire area. This armor of basalt protected the tors from weathering and erosion throughout the remainder of the Tertiary. Re-exhumation of the tors occurred either in the Pliocene as the result of accelerated erosion accompanying the major uplift of that period, or resulted from Pleistocene glacial and periglacial attack. Under the current geomor- phic regime the tors are evolving slowly by granular disintegration. Two additional factors which must be discussed with reference to this hypothesis are joint influence and the effect of Pleistocene glaciation in the area. The tor morphology is profoundly influenced by jointing which is characterized by two well developed vertical joint sets trending N 600 W and N 25O~,and by less regular horizontal or shallowly-dipping planar or curvilinear joints. Although the tors are probably formed in the outer section of the pluton, no evidence was found of primary joint structures described by Balk (19371, and there was only infrequent evidence of secondary crystallizations (in veins and dykes) on joint planes. Systematic vertical jointing is well developed in the quartz monzonite, This is well demon- strated by the near-vertical cirque walls which reflect the structural control of jointing, and the chasms cutting through the dome at Giant's Cleft. This jointing is probable tensile fracture,and is probably the result of stress developed during the late Cretaceous uplift of the area. Joint networks may have been further expanded during the minor Miocene and major Pliocene orogenies. Horizontal joints were frequently observed to terminate against vertical jointing,and occasional silicic veins present in the vertical joints were absent from horizontal fissures. The horizontal jointing is, therefore, judged to have formed at a later time than the vertical jointing, The lack of regularity in these joints suggests they are not the result of deep-seated extension but are produced in a near surface environment. The inconsistency of orientation of these joints also might reflect the influence of local stress conditions. Factors involved in this could not be concretely assessed,but may include some combination of topographic influence (chapman 1958, Chapman and Rioux 19581, weathering penetration (~homas1965), distribution of latent stress widal ale 1964) or other unknown factors. The well developed three-dimensional jointing of the quartz monzonite on McKeen Ridge is additional evidence supporting the proposed two-stage hypothesis because the existence of rectilinear jointing which is sufficiently dilated to allow the penetration of water is necessary in the two-stage morphogenesis proposed for tors by Linton (1955) and many others. Of particular interest was a tendency toward domical jointing seen in partial domes truncated alon-g cirque walls, but best exhibited by the Giantfs Cleft dome (see photograph 14). These low domes are marked by curvilinear jointing which becomes less regular and horizontal with depth, Photograph 14.-Giant's Cleft Dome as seen looking to the west from the spur ridge south of Ladyslipper Lake. Photograph 15,-Decapitated tors in the foreground (figure provides scale) with intact tors in the distance. Photograph looks to the north on the spur ridge south of Ladyslipper Lake. similar to jointing described by Jahns (1943). This indicates that the domes are not renewing themselves by continued concentric jointing. As the upper sheets are eroded and the lower, more horizontal, joint bounded sheets exposed, the dome will become flatter. This process is similar to the dome reduction described in Australia by Mabbutt (1952). Tors are present on the upper surface of the dome, a relationship also described by Thomas (1965) in Nigeria. Although much of the tor morphology reflects a joint control, no evidence was found in support of the frequent contention that it is variation in joint density that determines the pattern of deep weathering and ultimate distribution of tors i in ton 1955, Ollier 1960, Thomas 1965). Jointing, although infrequently exposed in inter-tor areas due to the grk cover, did not appear to be more dense there than joint intervals on the tors them- selves. An investigation of an essentially level, gr6s covered area between i tors in which no bedrock was exposed was carried out using a portable seismograph (~erraScout model R-70). Although several reversed course transects were made using this instrument, the bedrock topography beneath the griis and incoherent rock was too complex and of too small a scale toal- 3&h profile of this hidden surface to be constructed. Data obtained, however, showed an irregular bedrock relief to be present, with depths to bedrock exceeding six feet in some areas. Seismic velocities obtained were 1430-3440 ft sec-l for the weathered rock and 5250-7140 ft sec-L for the underlying bedrock. The shallow gr'& layer gave velocities of less than 900 ft sec-l. These values are similar to those obtained by Duncan and Dunn (1967) for the granite on Dartmoor, England. These findings show that no basal platform (proposed by Linton 1955) is present and that removal of the grzs and incoherent weathered rock would probably expose new tors, morphologically similar to tors present today, in inter-tor areas. In an earlier section of this thesis the general boundaries of the tor area were described and shown to have been determined by Pleistocene glacial action. The boundaries on the east side and south end of the tor area reflect truncation of the tor area by the backwasting of cirque walls, while the western boundary follows the trim line of valley glaciers in the Wall Creek basin. The contact of the Princeton group with the quartz monzonite forms the northern boundary. Valley glaciers were present in Lakeview and Wall Creek Valleys only during the incipient and waning stages of ice sheet development in the British Columbia Interior. The upper level of the ice sheet in Cathedral Park probably was below 7500 ft during the Fraser glaciation and a minimum 8400 ft during a pre-Fraser glaciation (a discussion of this is presented in the first section of this thesis). Much of the tor area was,therefore,submerged beneath this earlier ice sheet. The tors, however, show little sign of having been influenced by the ice. The principal flow of the pre-Fraser ice sheet split into two lobes near Princeton and was directed to either side of the Park, moving easterly and southerly through the lower Similkameen and Okanagan Valleys and south- westerly between the Tulameen and Upper Similkameen Rivers (Rice 1947). Ice presumably moved southerly through the P,ark area. The flow, however, was probably not very aggressive due to the area being outside of the P principal zones of ice movement and because of the damming effect of the upward slope. In Cathedral Pafk the only evidence of glacial erosion by a pre-Fraser sheet is at the southern end of Lakeview Valley where "U" shaped gaps occur between the drainage basins. This erosion probably resulted from the concentration of flow in these areas as the ice was constricted by the nunatak areas of Lakeview and Boxcar Mountains, the Sawtooth Range and l McKeen Ridge. The ice, in areas other than those just mentioned, may have been stagnant and capable of little erosion. This would explain the intact condition of the tors despite their having been overridden by glacial ice. Other writers, including Cunningham (19651, Caine (1967), Sugden (1968), Kaitanen (1969) and Pheasant and Andrews (19731, describe cases in which tors have remained essentially unaffected by submergence beneath continental ice sheets. These writers, along with Feininger (1971), suggest that continental ice sheets seldom accomplish substantial erosion except in the exceptional case (emphasized by Sugden 1968) in areas in which the flow of the ice was concentrated into narrow zones, producing adjacent areas of substantial and no erosion. Cunningham (1968) found tors to have been often displaced by ice movements with the upper blocks being rafted away from the lower portions of the tors which are rooted in bedrock. Limited rafting and other displacement of tor blocks did occur on McKeen Ridge. Rock plinths, interpreted asUdecapitated tors" similar to those described by Cunningham (1968), were present over substantial areas on the western slope of the tor area,and at elevations below intact tors on the spur ridge leading from the valley floor to the isolated tor group immediately south of Ladyslipper Lake (see photograph 15). Also found in the summit area of McKeen Ridge was a boulderized block with a weathering pit in a side surface which had definitely been displaced from a tor. Similar displaced tops of "decapitated torsf1were noted by Cunningham (1965). Most tors on the ridge have the appearance, however, of being intact, i.e., the upper boulderized blocks rest evenly on the bedrock bases and joint surfaces pass without disruption across the tor. Many of these tors have weathering pits (a subaerial microform) on the tops of the uppermost blocks. If the weathering pits are paleo-microforms having their origin before the Olympia interglacial which preceeded the Fraser isc cons in 11) glaciation,their presence is definite proof that the tors survived submerg- ence beneath continental ice. The alternative is that the pre-Fraser or other Pleistocene ice sheets principally removed only the armor of Princeton basalt from above the tors and was in the process of destroying the tors when glacial erosion was terminated at the end of the pre-Fraser glaciation. The upper surface of the Fraser ice sheet did not extend above 7500 ft,and neither it nor periglacial conditions associated with it could have displaced tor blocks on McKeen Ridge. The absence of a mechanism during the Fraser glaciation capable of rafting extremely large tor blocks, when coupled with the presence of a displaced block and weathering pit on the ridge summit, place the origin of the weathering pits to a time before the pre-Fraser glaciation, thus confirming the survival of the tors on McKeen Ridge despite submergence beneath the pre-Fraser ice sheet. This is consistent both with the inferred nature of flow within this ice sheet and other literature accounts of the relationship of tors and continental ice movements. The action of Pleistocene ice sheets and valley glaciers has also influenced the distribution of tors within the tor area. The rock plinth and gr& areas (see figures 5, 6a and 6b) are zones in which the upper parts of tors have been removed by glacial erosion,: leaving only the bedrock bases to mark the location of former tors. The steepness of the western slope of the tor area (15O) suggests that slope processes (including both creep and mass movements) are capable of moving detached tor blocks downslope. These processes would have been particularly active under the periglacial conditions associated with the Fraser glaciation. Although much of the talus would have been carried out of Wall Creek Valley by the glacier then present in it,some of the large talus blocks currently present on the valley floor are the remains of displaced tor blocks moved by slope processes. The continuous line of tors along the gentle summit of McKeen Ridge have survived in the zone where both glacial erosion and slope processes were least effective, At least some of these tors are thought not to have been submerged beneath the pre-Fraser ice sheet (i.e., those at elevations from 5400-8600 ft). The presence of tors on the spur ridge south of Ladyslipper Lake along the divide between two cirques is again an area where glacial processes would have been least aggressive. These tors also show that the tor area extended down the eastern slope of the tor area before the backwasting of cirques developed on this shaded valley-side cut into and largely eliminated the old tor surface. Although the action of glacial ice has created a sharp juxtaposition of the Eocene tor landscape with Pleistocene glacial features and had been the major factor in determining the general distribution of tors, it does not satisfactorily explain the location of individual tors, the large tor-studded masses or the ridge tors. Although variable intensities of erosion within the ice sheets and along valley walls by valley glaciers may explain part of the distribution of particular features, the original subsurface weathering pattern present during the Eocene formation of the tors seems the most likely agency responsible for the location of particular tors. The factors controlling the penetration of subsurface weathering during the Eocene are unknown. There was no indication that the variability of joint density was of importance. Factors which might have been important include joint openness widal ale 19621, micro-structures (~isdom1967, Thomas 19741, surface and groundwater drainage patterns, or other unknown factors. The location of individual tors, ridge tors and massive tor outcrops remains a puzzling feature of McKeen Ridge not explained by this study. Current Weathering Current weathering on McKeen Ridge is strongly related to the micro- environment present. Climatic conditions (see earlier discussion) include a moderate (30 inches) year round precipitation, a mean annual temperature below OOC, and probably six months in which temperatures remain below freezing. The entire tor area and ridge south of Quinoscoe Lake lie above the tree line, and are very exposed to winds which remove winter snowfall from the ridge,-allowing frost penetration to depths over 40 inches (70 inches was noted on Lakeview Mountain by Van Ryswyk 1969). The frost free season probably averages less than 20 days,with frost possible on any night. Climatic and exposure factors suggest that frost shattering would be the dominant geomorphic process on the ridge. As it is thought that the climate has not changed significently since the Pleistocene (some evidence suggests the tree line extended no higher than 8000 ft during the hypsi- thermal, (van Ryswyk 1969), and since weathering conditions in much of the Plei~tocene~wereundoubtedly periglacial, it is reasonable to regard frost action as the dominant weathering process in the area since the onset of the Pleistocene. Abundant evidence of frost accion is present on McKeen Ridge, the Sawtooth Range and Lakeview Mountain. Minor landforms developed on the four rock units (princeton basalt, Nicola basalt, Lakeview granite, Cathedral quartz monzonite) in areas other than the tor zone consist of solifluction lobes, patterned ground and felsenmeer. Although these landforms undoubtedly had their origin in the Pleistocene it is probable, in view of the climate present today on the ridge, that they are continuing to develop (though more slowly) under contemporary conditions. The Princeton and Nicola basalts are particularly susceptible to frost-riving because of the dense joint networks (joint intervals are 18 inches or less). Jointing in the Nicola lava probably developed during periods of tectonic deformation, while those in the Princeton group are mainly contraction joints. These planes allow water entry and highly effective freeze-thaw action. Similar frost-shattered material is present on the granitic rocks. The evidence of extremely effective frost action outside of the study area contrasts sharply with a complete absence of frost shattered material within it. No angular talus or other evidence of frost action was present. The ineffectiveness of frost action cannot be explained on a lithologic basis as frost shattering is effective on the quartz monzonite outside the study area. It is explained, however, by the weathered state and qualities of the quartz monzonite in the tor area. The quartz monzonite in the tor area is in a friable state, a condition traced to subsurface weathering during the Early Tertiary. Since the re-exhumation of the tors during the Pliocene or Pleistocene the tors have probably been evolving by granular disintegration. Confirmation of this can be seen in the absence of frost shattered material in the area and the ubiquitous presence of gr& soil horizons. It is noteworthy that the action of this weathering process probably results in little change in the form of the tors. Demek (1964a) cites tors in Czechoslavakia developed in coarse- grained granites which retained their form during the Pleistocene while tors formed in other rock types were extensively altered by frost action. Although the susceptibility of the quartz monzonite in the tor area to undergo granular disintegration can be traced to its partially weathered condition, the actual mechanism causing the detachment of individual crystals remains less certain, Granular disintegration is a response of the rock to stress having its origin in physical and chemical weathering processes. Physical factors capable of producing the necessary stress include thermal expansion, expansion resulting from moisture absorption, stress due to salt crystal- lization, and possibly tectonic stress latent in the rock itself. chemical factors are not different from normal weathering processes and include continued hydration, hydrolysis, and solution. Kessler and Hockman (19.50) investigated the expansion caused in granitic rocks by temperature change and moisture absorption. Temperature change produces stress by instituting a thermal gradient, because crystals of different sizes are present, and be- cause the constituent minerals expand at different rates, amounts, and in different crystallographic directions. The shallow absorption of water is thought to produce unequal stress in the rock surface. Kessler and Hockman (1950) found that expansion over the temperature range -40•‹ to 60'~ gave 6 o thermal expansion coefficients ranging from 4.8-8.3 x 10- per C,while - 5 expansion due to moisture absprption averaged 3.9 x 10 . Thermal expansion is more important than moisture absorption as the total amount of expansion 0 due to moisture absorption is equivalent to only that occurring in a 6 C temperature change. The two factors may augment one another, and while their effects may not be noticeable over short periods,they do contribute to weathering. The evidence outlined above supports the contention of Leigh (1968) that insolation weathering may be an important factor in the granular disintegration of granitic domes in Australia. The weathered state of the tors on McKeen Ridge indicates that the minor expansion due to these factors is not significant as it could easily be absorped in the weathered quartz monzonite without causing further disruption, Freeze-thaw action (mi~ro~elivation)involving stress produced by the volume expansion of water on freezing (approximately 8%) is frequently proposed in the literature is capable of producing granular disintegration (~emek1964a,b, Dahl 1966). This process can be effective only where voids are nearly saturated-no pressure will result where expansion is accomodated without filling a void. The effectiveness of mi~ro~elivationis somewhat in question. Kessler et a1 (1940) subjected saturated granitic rock cores to 5000 cycles of freezing at -120 C for six hours,and thawing for one hour in water. No changes were observed at the conclusion of the tests, even in specimens which had undergone considerable weathering prior to the test. These results question the legitimacy of microgelivation. Similar tests (freezing hours at -16 0F, thawing for one hour) were conducted over a 30 day (90 cycles) period during the course of laboratory analysis of weathered fresh and indurated Cathedral quartz monzonite done as a part of this thesis. No change in any specimens, even the weathered rock which was friable by hand, were noted. Mi~rog~livationis, therefore, judged to be an ineffective mechanism in causing granular disintegration. Although freeze-thaw action seems to be an ineffective micro-scale weathering process, the susceptibility of some rock to disintegration under conditions of temperature cycling through 00 C is beyond question. A possible mechanism was developed by Dunn and Hodec (1966). The writers examined the origin of frost sensitivity in carbonate rocks and using a differential thermal analysis technique, found that water in sound rock (rock known to be unaffected by frost cycling) froze upon super cooling to -loOc,while most water in unsound rock remained unfrozen at -400 C. The apparent frost sensitivity could not be explained by volume change. The writers proposed that water molecules (which are highly polarized) would become absorped on to the negatively charged clay surfaces (i.e., hydration of clay). The ordered water would be bonded to the clay surface more strongly than the bonding in ice and would be effectively unfreezable. The water would have high shear strength and rigidity. As water expands rapidly on cooling below 0 3.8 C, the authors postulate that it is pressure evolved in this expansion that ruptures the rock. This process is effective because the rate of expansion of the ordered water is two orders of magnitude greater than the rate at which rocks con- tract on cooling. Strict application of the theory requires small fissures or pore spaces. Falconer (1969) suggests a maximum space of 5 microns in which this effect can occur. Initial weathering may result in the presence of clay minerals in micro-fissures in granitic rocks. In unaltered rock, water entering micro-cracks could become oriented as the exterior surfaces of tectosilicates normally have a negative charge (a common case is the adhesion of water to glass). Ordered water layers from opposing sides of pores or fissures would be electrical opposites and repel one another. Experiments by Dunn and Hudec (1966) show the mechanism to be important in determining the frost sensitivity of argillaceous carbonates, while Falconer (1969) proposes it to be a mechanism producing glacial detritus. On the McKeen Ridge it is possible that this mechanism acts in conjunction with simple hydration of clay minerals,or works alone in widening micro- structures. It is again not regarded as a major cause of the granular disintegration. A further cause of granular disintegration is the crystallization of salts in pores and fissures. Kessler et a1 (1940) subjected samples of granitic rocks to salt crystallization in cycles of alternately soaking the samples in a saturated solution of sodium sulfate (~aSO ) for 17 hours 2 4 and drying them for 7 hours at 1050 C. All specimens suffered substantial disintegration,and a 10% weight loss occurring in a minimum of 14 and average of 42 cycles. The results indicated that salt crystallization can be a significant factor in the weathering of the granitic rocks. Similar tests were conducted during laboratory work for this thesis on fresh, weathered and indurated samples of the Cathedral quartz monzonite using solutions of sodium sulfate, sodium chloride and sodium carbonate. Substantial disintegration of the weathered sample occurred after 11 cycles, while the indurated and fresh specimens suffered from only mild disinte- gration after 18 cycles. The early disintegration of the weathered rock resulted from its substantially greater porosity and friable condition. Specimens of the fresh, weathered and indurated quartz monzonite were dried at 105~~for 48 hours, and then soaked in a dye (blue methylene) for 48 hours. The dye penetrated only a few millimeters into the fresh and indurated specimens, whileitpeneeated over six centimeters into the weathered samples. Results are not reproduceable for the salt crystallization or dye penetration tests because hand specimens of irregular size and shape were used rather than uniform rock cores. The results do qualitatively indicate the greater susceptibility of the weathered rock to salt crystallization and its greater ability to absorb water. The implications of the similarity of indurated and fresh samples will be more fully discussed in a later section. Substantial theory and observation supports the position that salt crystallization is an effective weathering process. Weyl (1959) has shown that significent pressures can be exerted by crystallizing salts and that voids do not need to be completely filled by the crystal. Pressure exertedwas related to the degree of local supersaturation,and he showed that crystals could continue to grow in a pore even while extending down a capillary. Uellman and Wilson (1965) contended that salt crystallization was underrated as a weathering agent, and related crystal growth and pressure evolved to pore size. Large crystals grow at the expense of smaller crystals, and more importantly, a large crystal continued to grow against the constraint of a completely filled pore, Pressure would build in a pore until mechanical rupture occurred or the crystal ceased growing in the pore and extended down the capillary. Rupture would be favored where pore sizes are large (or more favorably where large pores are separated by micro-porous regions), and where the michanical strength of the weathered rock is low. Variation in mechanical strength and pore size could possibly explain the varying susceptibilities of rocks to granular disintegration. The process would be expected to be more effective in weathered rock because to its low mechanical strength. The reduced mechanical strength of weathered Dartmoor tor granite was demonstrated by Duncan and Dunne (19671,and granular disintegration is occurring on the tors there i in ton 1955). The weathered tor quartz mon- zonite,having low mechanical strength and high moisture absorption, would be expected to be susceptible to this type of weathering attack. Wellman and Wilson (1965) proposed that the shape of some tors and inselbergs was due to granular disintegration. This was disputed by Bruckner (1966) who argued the scale of the process and landforms precluded the salt crystallization from having a major role in the formation of the features, although it was effective in subsequent subaerial denudation of the features. Evans (1970) discussed the theory and summarized evidence for salt crystallization. In particular he found it to be an active process in the dry valleys of Antarctica where it was regarded as generally more important than freeze-thaw in the development of tafoni. The rudimentary experimental evidence with salt crystallization using the Cathedral quartz monzonite and theoretical considerations (i.e., weathered condition and multiple wetting and drying cycles) indicates that salt crystallization may be an effective process resulting in the slow disinte- gration of the tors. If this were true, weathering should be most rapid near ground level. Kessler et a1 (1940) showed granites to have significant abilities to transmit water by capillary action. Average amounts of water 1 transmitted through 2.1 X 2.5 inches rock cores were 0.81 grams water day,- 1 while a high of 7.5 grams water day - was observed in a partially weathered sample. Evaporation of groundwater could result in the precipitation of salts in the rock, creating stress lending to its disintegration. Most tors on McKeen Ridge, however, did not show marked cavernous weathering along their bases. This is not interpreted as indicating a lack of effec- tiveness of salt crystallization,but reflects the probable low water trans- mission ability of the indurated surface of these tors. Salt crystallization is,however, regarded by this writer as an effective process on exposed weathered quartz monzonite on the tors. Release of latent stress could result in, or assist granular disinte- gration. This might be residual tectonic stress (~ieslin~er1960) or form related stress (~erbierand Scheidegger 19691, although neither author proposes stress release to operate at the scale of granular disintegration. The possibility must not, however, be discounted. Stress evolving from chemical weathering includes continued alter- ation of minerals (particularly biotite) to secondary minerals, hydration of clays and removal of material in solution. This differs in no way from normal chemical weathering, in which stresses are built up and the integrity of the rock reduced. These factors are probably active in reducing the surface of the tors, which is commonly indurated. Granular disintegration on the indurated skins must occur at a slow rate because its low ability to absorb water indicates it willweather almost as slowly as a fresh rock exposure, i.e., the micro-environment of the indurated tor surface is arid due to the high runoff (low absorption) of the rock surface. Granular disintegration is regarded to be the dominant weathering pro- cess on the tors. It is principally the result of continued hydrolysis, hydration and solution, although on non-indurated tors salt crystallization is also a potentially effective process. Micro-gelvation is not a signif- icant process. The absence of vegetation on the tor surface means biotic weathering is unimportant. The sparse lichen cover gel he be lanta) present on some tors is not thought to have a substantive weathering effect. Lichens are generally regarded as having little decomposing ability,although a recent investigation in Hawaii by Jackson and Keller (1970) indicated that lichens were significant in that area. The granular disintegration (and weathering in general) must be limited to the months in which temperatures rise above the freezing level with no weathering occurring during the long winter season. Micro-forms Minor landforms often found in association with tors include core- stones and blockfields, weathering pits and lapies. Corestones are the depositional counterpart of tors, being spheroidally-weathered boulders isolated from the weathering front in a matrix of weathered material which are deposited on,or appear at the surface as the fine matrix material is removed. Few corestones are present on the ridge itself. This is not entirely unexpected in view of the Pleistocene environment and exposure of the area. Two corestones found were of particular interest. One was approximately 46 inches in diameter and embedded in grus material (see photograph 9). This corestone had three concentric indurated shells ranging from 1-1:s inch in thickness. Concentric weathering shells have been reported by a number of writers, and are thought to result from inward penetration of weathering along micro-cracks (~isdom1967) followed by separation of a weathered layer as stress developing as lower density secondary minerals are formed, exceeds the tensile strength of the rock (chapman and Greenfield 194-9, Simpson 1964). Other spheroidal structures, not necessarily involving the separation of distinct,shells, are regarded as evolving by a liesgang mechanism (~ugustithisand Otteman 1966, Ollier 1967, 1971). The thickness of the layers reflects the coarse texture of the quartz monzonite. Coarse- grained rocks have a greater depth of water absorption than fine-grained and volcanic rocks and give rise to thicker shells (0llier 1971). Another interesting corestone was an apparent partial shell of a corestone, the shell being 3-7 inches thick and a diameter of 30 inches. Bisdom (1967) proposed that coalescing micro-structures would createa dense fracture network in the center of a corestone. This may partially explain the absence of small boulders in deep weathering debris as the dense web of micro-structures causes crumbling of the boulder to g;;s (another factor, of course, is accelerated weathering as the ratio of surface area/volume of the boulder increases). Crumbling of the center of a boulder prior to complete weathering of the outer section conceivably created the partial shell present today. A final corestone feature is the boulder field of corestones on the i lower portion ridge leading southward to the valley from the isolated tors south of Ladyslipper Lake. Boulderfields of spheroidal boulders (rather than angular, frost-riven debris) has been described by Demek (1964b), Matsumoto (1964) and Caine (1968). Matsumoto 61964) reported some block- streams in Japan to have formed by simple removal of the fine-grained matrix from a deep weathering regolith while others had undergone Pleistocene mass movement. In Czechoslovakia, Demek (1964b) regarded the blockstreams as having been deposited in place by accelerated erosion,and regarded the degree of exposure of boulders on slopes to reflect the intensity of denudation on slope segments. In Tasmania, Caine (1968) regarded block fields to be pro- duced over four stages: 1) Production of blockfield material by Tertiary deep weathering, Pleistocene glacial erosion, periglacial frost action and interglacial weathering 2) Flow of blockfield material and unconsolidated matrix material during the Pleistocene 3) Post-Pleistocene eluviation of interstitial fines 4) Current weathering (adopted from Caine 1968) The wea-thered condition, indurated shells and rounded form of the boulders in the blockstream south of Ladyslipper Lake,indicate they are of Tertiary origin, while the regular orientation of ellipsoidal boulders with the long axis parallel or perpendicular to the slope demands deposition in their present position by some type of mass movement, probably occurring in the Pleistocene. An evolution similar to that proposed by Caine (1968) seems likely for this blockfield on McKeen Ridge. A final interesting feature found in the upper surface of many tors in Cathedral Park were shallow rock basins called llgnammall, "weathering pitsf1or "panholesf'. The origin and evolution of these curious features of this type have been the subject of much speculation (~entworth194.4, Cunningham 1964, Corbin and Twidale 1963, Hedges 1969). A number of hypo- thesis proposed for the morphogenesis of weathering pits were discussed in an earlier section of this thesis. The weathering pits present on Cathedral Park tors are morphologically similar to other weathering pits described in the literature, The depressions , t are most often circular or elliptical in plan,with diameters ranging from t i 6-52 inches and depths froin 2-18 inches. Most weathering pits were located on level or shallowly inclined summits of tors. The maximum rock slope on which a weathering pit was present was 200 . Typical weathering pits had flat bottom, perpendicular sides, and overhanging rims around al1,or a portion of the upper portion of the weathering pit. These rims result from the weathering pit widening after it breaches the indurated veneer on the tor surface and begins developing in the more easily weathered underlying rock (White 1944). Overhangs usually were in the 2-4 inch range,but an overhang of 14 inches was observed in one weathering pit. No preferred orientation for overhangs was found and the location and extent of the overhangs appeared to be determined by variation of thickness of the indurated crust. Some weathering pits had deep grooves cut into one side providing an outlet for water. Similar features were described by Cunningham (1964). The "gutters" did not extend to the floor of the weathering pit. Most weathering pits rely on evaporation for removal of standing water trapped within them. PH values of standing water were in the 4.8-5.4 range, close to values obtained from weathering pits in Czechoslavakia (p~4.5-5.5 Demek 1964a) and Australia (p~5.5 Leigh 1968). Concentrations of dissolved solids in the standing water of nine weathering pits were measured with a portable dissolved solid meter. Values obtained ranged from 28 to 54 ppm. Deepening of the weathering pits is probably not due to frost action (proposed by Dahl 1966 in Norway) as the effectiveness of microgelivation as a weathering process is doubtful. Deepening could result from solution, (LeGrand 1952) which is a viable process in view of the moderately low pH values (Baglord et a1 19631, continued hydration and hydrolysis (Bakker 19601, crystallization of mineral salts (~emek1964a),or a combination of these factors. Salt crystallization in particular would seem to be an effective process as progressively higher concentrations of solutes would be expected as evaporation occurred. Many weathering pits had g& type debris on the bottom, probably resulting from granular disintegration. This process would be more effective below the indurated zone and assists in explaining the overhanging rims. Other weathering pits had no debris in the bottom. As it is unlikely that large caliber material of this type could be removed during periods of overflow, these pits would seem to be developing slowly by solution and other chemical weathering, rather than granular disinte- gration (at least in recent times). Weathering pits develop under subaerial conditions. Those present on McKeen Ridge are likely to have first developed during the Late Tertiary exhumation of tors, with development continuing into Pleistocene and recent times. No weathering pits were found on recently exhumed tors at the quartz monzonite-Princeton group contact. No anamolous material of glacial deposition was found in weathering pits. Dating of the weathering pits is problematic in the absence of definite evidence. The overhanging rims, however, do indicate that the induration was present before development of the weathering pits. Initiation and deepening of weathering pits, although a fairly rapid process in geologic time scales, is probably slow in terms of historical time spans and it is unlikely that they have developed in the short period since the Pleistocene. One of the most puzzling of problems presented by weathering pits is the origin of the initial depression. Mechanisms proposed include the pre- sence of aggregates of solu ble mineral (~atthes1930), accelerated weathering beneath patches of moss (White 19441, small scale extension jointing a lank 19511, and joint influences orbi in and Twidale 1963). These hypothesis were inferred from field evidence. The origin of some weathering pits on McKeen Ridge may be due to these mechanims, but a different mechanism, outlined below, must be invoked for at least some of the weathering pits. The existence of more than one indurated crust on some sections of tors was noted in an earlier section. These partial shells could often be pried apart with a geologist's pick. Cohesion between layers was low, apparently due to water penetration and weathering action along the inter- face. On the upper surface of one tor a small ttblistertt9-14 inches across and 26 inches long of indurated crust occurred in the indurated layerwhich covered the entire tor surface. This blister was pried from the tor surface, exposing one crude rock basin and two incipient basins. The basins were filled with finely weathered rock material, Removal of the indurated blister and fine materials revealed three incipient weathering pits. The micro-environment beneath the indurated blister was more moist than that of the rock surface, and was suitable for accelerated chemical decomposition of the underlying rock. The removal of the indurated blister with the rock pick accelerated a process that would have occurred naturaily, probably as the result of freeze thaw action. The frequent presence of multiple indurated shells on portions of tors suggests that the mechanism outline above may explain the origin of many weathering pits on McKeen Ridge and helps account for their irregular distribution. In view of the strong probability that weathering pits are a convergent landform, it would be preseumptuous to explain thedorigin of all weathering pits in this manner, although it is definitely responsible for some of the features, Concluding Remarks The examination of literature accounts concerned with tors and related subjects in previous sections of this thesis produced a number of generali- zations about the nature of the landforms. Although tors have been regarded as resulting from periglacial frost attack, valley-side downwasting, parallel escarpment retreat and simple solution, or they have been regarded as struc- tural landforms, those possessing morphological characteristics described in the text are attributable to a two-stage morphogenesis. The form and evolution of the features reflects the interaction of regularly jointed bedrock with chemically reactive groundwaters. Jount systems guide the weathering attack by allowing the penetration of groundwaters into otherwise impermeable crystalline bedrock. The closure of joint fissures marks the vertical limit'of weathering penetration. Sub- surface chemical weathering is best characterized as a spheroidal process which progressively boulderizes joint-bounded blocks. Chemical weathering is an azonal process and the degree of leaching the most important factor in determining the type of residual material formed. Deep weathering will occur when the rate of subsurface decomposition of the bedrock is greater than the removal of debris by surface erosion. Deep weathering and tors are not restricted to particular climates and cannot, in the absence of other evidence, be regarded as indicators of particular climatic conditions. Although tors most frequently occur in coarse-grained granitic rocks, they occur on a wide variety of igneous, metamorphic and sedimentary rock types. In all cases the influence of the lithology and structure of the particular bedrock is important. Another important facotr in many landscapes is the susceptibility of granitic rocks containing accessory biotite to I t mechanical disaggregation after limited weathering. All chemical weathering is not of meteoric origin. A hydrothermal stage is part of the normal sequence of crystallization of an intrusive magma. Non-meteoric alteration of this or other origin may act separately or in conjunction with meteoric alteration to produce tor landscapes. Recognition and assessment of the influence of non-meteoric weathering in these cases presents a formidible problem. Tors exposed to subaerial conditions evolve very slowly, surviving to be paleo-landforms of immense age. Most torswhich have evolvedby a two-stage process had their genesis in the Tertiary. The resistence of tors to destruction by subaerial processes includes their ability to survive sub- mergence beneath continental ice sheets. The conditions needed for deep weathering, when coupled with the questionable erosive power of continental ice sheet,indicated that deep weathering landscapes and tors may have had a widespread distribution in cratonic areas of.the northern latitudes during the Tertiary. The tors on McKeen Ridge are shown to be paleo-landforms of immense age. They are formed in a coarse-grained quartz monzonite pluton of Jurassic age which was first exposed to meteoric weathering at the beginning of the Tertiary. Environmental conditions at this time included a low relief "peneplain surfaceft(and associated low intensity denudation), and a warm, moist and temperate climate. The tors evolved in the subsurface of a low ridge present in the area. They were exhumed during the Eocene and then buried beneath the fossiliferous freshwater sediment and volcanics of the Princeton group approximately 50 m.y. ago. Four factors, the geomorphic and climatic conditions of the Eocene, the presence of weathered quartz monzonite in the Princeton sediment, the weathered state of the bedrock in the tor area today, and the morphology of the tors themselves, establish the the subsurface origin of the features. The tors were protected from weathering processes throughout the re- mainder of the Tertiary by the overlying Princeton strata,and were re-exhumed during the major orogeny which began late in the Pliocene. Many, if not all, of the tors have survived submergence beneath Pleistocene ice sheets. The tors are present today on an alpine ridge and occur in close association with a wide variety of glacial and periglacial landforms. The features show no evidence of Pleistocene or recent macro-frost shattering and are evolving slowly by granular disintegration. Minor features found on many tors include an indurated crust and weathering pits. 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