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184 XtR. C. T. TREOaatANS 0.'r X ~tASS Or ANH~DI~ITV. [ffune 1913,

11. On a MAss of AN~nRI~r in the MAa~rSlAN LIMES~O~rE at HA~TLE~OOr, and on the PrRXfIA~ of SOCTn-EASTrR~r DurmAlt. :By CrIARL~ TAYLOR TRECH~A~'. B.Sc. (Communicated by :Prof. E. J. GARWOOD, M.A., V.P.G.S. Read January 8th, 1913.) [PLATE XXII--M,te.] CO~T~TS. Page I. Introduction ...... 184 II. The Mass of Anhydrite in the Magnesian Limestone at Hartlepool. 185 III. Borings in the Magnesian Limestone where it is protected by .Red Beds ...... 193 IV. The Former Presence of Soluble Constituents in the Magnesian Limestone ...... 195 V. :Nature of the Shell-Limestone and the Associated Strata .... '. .... 199 VI. Typical Sections and Exposures in the Hartlepool Area ...... 203 (1) Hartlepool Foreshore. (5) Castle-Eden Dene. (2) West Hartlepool. (6) Hardwiek Done. s Blackhall Rocks and (7) Hart Quarries. the coast-section to (8) Blackhall-CollierySinking the north and south. (1909-13). (4) Hesleden Dene. VII. Notes on the Pal~eontology of the Hartlepool Area ...... 214 VIII. Summary of Conclusions ...... 217

I. IN'rRoI)UCTIOX. THB exposures of Magnesian Limestone in the area under dis- cussion in the present comnmnication are indicated on the 1-inch Geological Survey ~Drifg~ Map, Sheet 103 N.E. (New Series, Sheet 27), with the exception of the fine continuous sections of Castle-Eden, Hardwiek, and Hesleden Denes: these are only indicated in part, and seem to have been overlooked by the sur- veyors. No attempt is made to distinguish the divisions of the Magnesian Limestone. Otherwise I know of no paper dealing with the district as a whole, though scattered references to the exposures of the coast-section and Castle-Eden Dene occur in various publications. The isolated outcrops of Upper Magnesian Limestone with their associated anhydrite-mass, on which ~he two towns of Hartlepool and West Hartlepool are built,, are bounded on the west and north- west by a valley filled with Glacial and superficial ddbris, probably connected with the watershed of the pro-Glacial Tees Valley. The nearest outcrops of Magnesian Limestone occur nearly 2 miles away to the west, and nearly 3 miles away to the north-west along the coast. The area is bounded on the south-east by the fault, everywhere hidden and therefore largely problematical, which brings the Red :Beds down against the Magnesian Limestone, and is marked on the Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015 u 69. ] IN THE ~IAGNE$IAN LI~IESTONE AT H~RTLEPOOL. 185

Survey maps as extending in a straight line from West ]-Iartlepool to a point south of Darlington. The levels of the limestone in borings north and south of this fault at West Hartlepool show a difference of about 700 feet, and so the southward throw of the fault is probably of this magnitude. Its exact point of contact with the sea-coast would seem to be where the road from Seaton ~Carew to West ttartlepool crosses the railway near the saw-mills and engine-shed. The Red Beds, well exposed at Long Scar and Seaton Carew, are not touched upon in this paper, except as the protective covering of the underlying Magnesian Limestone. To the west and north-west the typical sections of Magnesian Limestone on the coast and in the various ravines and isolated outcrops are described as far north as Castle-Eden Dene, and as far west as the limit of the Magnesian Limestone in that dene. The whole south-western portion of the area is hidden by Glacial drift, and does not concern this paper. Glacial action has brought about an intense deformation of the limestone in parts ; this is especially noticeable in some of the Upper Limestones of the coast-section, and makes a detailed mapping of the coast an almost impossible task. The effect seems, however, to be a comparatively superficial one. As may be supposed, on account of the internal collapse of parts of the Magnesian Limestone, the dip of the beds is a very variable one; but the prevailing dip is a few degrees eastwards or south-eastwards, corresponding to the general slope of the country towards the sea. The work on the outcrops and sections in the area is based chiefly on pala~ontological evidence.

II. THE MASS OF ANHYDRITE IN THE Mk6NESIkN LIMBSTONB AT ~[ARTLEPOOL. The observations here detailed deal primarily with a large mass of anhydrite and the associated gypsum, which is proved by a boring and other indications to occur in close proximity to the Upper Magnesian Limestone upon which the towns of I{artlepool and YVest Hartlepool are built. To the subsequent denudation and erosion of this mass the harbour of Hartlepool owes its existence. Had the 3[agnesian Limestone extended without an interruption from its occurrence on Hartlepool foreshore to its second outcrop at the gasworks at West Hartlepool, it is clear that the inter- vening ' slack' or valley which accommodates the harbours of the two towns could not have existed under the given conditions. Thus the harbour of Hartlepool, situated as it is in a somewhat anomalous and unexpected position on the coast, proves to be in respect to its mode of origin in many ways a very interesting and unusual phenomenon. The presence of gypsum in the harbour might have been inferred without the evidence of any boring, from the fact that masses of o2 Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

186 ~rR. c. T. TREeIt.~tX~X OX .t ~tASS OF AXnYOI~ITE Effune 1913, that material often of very large size, reaching several hundred- weight, have frequently been observed in the Boulder Clay filling the 'slack,' and are constantly brought up by tile harhour-dredger from the depression occupying the area between the two outcrops of Magnesian Limestone, and also from the bed of the sea out towards the bay. Their extension northwards and westwards is strictly limited to the area of tile Hartlepool slack, but eastwards and south-eastwards their distribution is uncertain; though I havo been informed, on not very sure authority, that they extend across the mouth of the Tees and have occurred as far sou[h as Redear. These masses of gypsum seem to be true glacial boulders, torn up by a glacier passing in a south-easterly direction from the then exposed surface of gypsum, and embedded in the Boulder Clay. Before the coast was so largely encroached on by buildings, they seem to have been exposed in several places, where the material was largely quarried tbr carving small ornamental objects. The boulders are variable in colour, generally white but often red, pink, or brown, and all seem to be pure gypsum without an- hydrite or limestone. The promontory upon which Hartlepool is built is an isolated outcrop of Upper Magnesian Limestone, and is roughly oval in its present outline, lying with its longer axis oriented north-westwards and south-eastwards, measuring about half a mile in width and rather over a mile in length, from its first appearance at Partoll Rocks on the north-west to its disappearance beneath the sea on the south-east near the end of the new breakwater. About five-sixths of a mile west of the exposure the Upper Magnesian Limestone is again seen well exposed in the railway- cutting near the gasworks at West Hartlepool: and it is further observable, skirting the harbour for a distance of nearly a mile. The intervening slack is filled in with Boulder Clay, upon which rests a submerged forest or peat-bed, overlain in part by blown sand and superficial deposits. In these Glacial and recent beds the various harbours and timber-ponds of the two towns have been excavated and constructed at different times. The first solid rock met with on piercing this covering of super- ficial deposits is a bed of anhydrite of great thickness, which is found to be altered to gypsum on both its upper and nether surfaces. Unfortunately, but one boring is available showing the true thickness of this bed, so our knowledge regarding its lateral extension and thickness in other directions can be inferred only. There was nothing to indicate that the strata passed through were in other than a horizontal position. If the uniform ' slack' or depression in which the harbours are constructed is entirely due, as seems beyond question, to the erosion of the anhydrite, then the mass should have an oblong or elliptical outline with its longer axis lying north-west and south-east, and measuring possibly a mile and a half in length and nearly a mile in width. The boring in question was sunk in 1888 by ft. Vivian & Co., of Whitehaven, by the diamond-boring process giving 6-inch cores, Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

~'ol. 69. ] I~ ~s ~AG.~ESIAX LI.~ES~O-~E A~ nAn~LEroo~. 187 at the Warren Cement-Works at Hartlepool, at a spot exactly a sixth of a mi]e from the nearest known outcrop of Magnesian Lime- stone which occurs beneath the iron railway-bridge at Throston, and on the north-west or inner side of the outcrop of that rock upon which Hartlepool stands. The following section was passed through in descending order "-- Thickness in feet inches. Blown sand ...... 22 0 Submerged forest- or peat-bed ...... 8 0 Feet~ Red clay ...... 18 ] Red clay with small .~tones ...... 6 [ Glacial Dark clay and stones ...... 39 ~- deposits. ) '" 67 0 Red clay ...... 2 I Soft limestone (or boulder) ...... 1 Red clay ...... 1 J Gypsum ...... 1 5 Anhydrite ...... 265 7 Dark-grey limestone passin~ into a broken 0 limestone with abundance of water, j ...... 38

The solid rock was met with at a depth of 97 feet, and consisted of gypsum, passing after a further depth of 17 inches into a bed of pure anhydrite of the unusual thickness of 265 feet 7 inches. The anhydrite was more or less streaked and banded with Magnesian Limestone in its lower part, the bands of limestone occurring in irregular horizontal fragments and layers, which become larger and more numerous towards the base. The anhydrite was again partly altered to gypsum at the base of the mass, and passed quite contbrraably down into a bed of very hard dark-grey :Mag- nesian Limestone, which was met with at a depth of 364 feet and pierced to a depth of 38 feet, when a bed of broken rock was met with and a good feed of water was obtained ; this water proved to be highly charged with solids, chiefly chlorides and sulphates.

I recently undertook a detailed examination of the cores of the boring which are still preserved, with the view of determining, if possible, the exact horizon of this limestone, its composition, and the nature of its residues. Although the rock had long been supposed to be unfossiliferous, by earefuUy breaking it up three recognizable species of tbssils were obtained. The cores of the limestoue are now very much mixed up, out in the 38 feet of gypsiferous rock underlying the anhydrite-bed at least three varieties are met with, as follows (in their apparent order of superposition) :~ A. Limestone interbMded with anhydrite to-"~ wards the lower margin of the auhydrite- / bed. A hard, compact, dense, dark-grey ~- No fossi!so rock, containing much anhydrite but no I gypsmn. J B. Immediately underlying the anhydrite-bed.'l A very hard, dark-grey, dense, fine-grained limestone having fissures and cracks filled No fossils. with gypsum. The rock is breeeiated in part, the broken fragments being re- [ cemented with gypsum. .J Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

188 mr. c. x. TnECrrMA~;N O~t X MASS 0F A.~arDaITS [June I913,

C. Tough, coarse-grained, highly gypsiferous'~ limestone, darker in colour than B. The [ Strophalosia lamellosa Gein. ; gypsum occurs in cracks and fissures, and }- in poor preservation, but clearly is also largely incorporated with the mass [ recognizable, l of the rock. J D. A very dark, highly crystalline, but friable "/ ETithyris elongata Schl. & and'porous limestone, much broken up in [. Bakevellia ceratophaga Sehl. parts. This is the broken limestone f both fairly numerous. whence the water was obtained. J " 1 I have since detected traces of bryozoa, and a small obscure gasteropod in this. bed. The following analyses of the four samples were made, excluding the gypsum and anhydrite, so far as it was possible to remove these substances by hand before analysis :-- A. l B. C. D. Insoluble residue : ...... 2"03 2"78 0"27-1"00 0"82 0"62 Water, organic matter, etc .... trace trace trace 3"17 2"29 AI.-Oa, P20~ ...... trace trace 0"15 trace 0"20 FeO ...... 0"61 0"83 1"56 1"06 5"37 CaC03 ...... 38"16 52"36 56"00 42"86 56"39 MgCO:~ ...... 32"80 45"01 42"79 33"92 3~'97

CaS04 ...... 27"40 -- 0"18 19"04 1"17 1 Calculated without the anhydrite which is disseminated through the rock. -" The insoluble residue of all these samples is very much alike, and oilers the following peculiarities :-- (1) Comparatively large quartz-grains: some with idiomorphic outlines, others irregular, and both full of inclusions. The inclusions consist of crystals and crystal-agga'egates and groups of pyrite, showing the cube, octahedron, and pentagonal dodecahedron, mostly in combination one with the other. The idiomorphic quartz-grains show clear margins, where the perfect crystal bas subsequently grown round a normal irregular grain with pyrite inclusions. (2) Free pyrite in ag~'egates aud free crystals of the above-mentioned forms and combinations. (3) Highly refractive groins resembling zircons with rounded angles. (4) Dichroic minerals resembling tourmaline in occasional crystals. Only in one limestone at the surface (concretionary series) have I yet seen residues of quartz enclosing pyrite. The limestones obtained in this boring are unlike any member of the series exposed at the surface. Their dark colour is largely due to organic oily matter, but more especially to impure unoxidized iron salts chiefly present as ferrous carbonate. The highly mag- nesian character of all of them will be noticed, a feature indicating the original state of deposit of the formation. Sample A, the rock interbedded with the anhydrite, is assumed, I think safely, to be a limestone, if not in the condition of deposition, at least with its constituent elements present in the proportions in which they were originally deposited. These samples are com- pletely enclosed or encased in the bed of impervious anhydrite. The rock is hard, dense, and compact, recalling in this respect any normal Carboniferous or other limestone. It is entire]y unbrecciated and undisturbed. It contains a large quantity of anhydrite but no trace of gypsum, the anhydrite being arranged in parts in plates and aggregates of tabular formless crystals throughout the rock, recalling, as will be shown, in appearance the hollow negative Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

Vol. 69. ] IN THE MAGNESrAN LIMESTONE AT HARTLEPOOL. 189 pseudomorphic aggregates found in several beds of Magnesian Limestone at the surface.

The gypsiferous limestones underlying the anhydrite represent an intermediate stage between the above-described rock and the completely gypsum-free rock as it is exposed at the surface. They are in a condition comparable with the limestones underlying the Red Beds south of the West Hartlepool fault, and in other areas where the Magnesian Limestone has been partly protected. Re- moval of the protective covering, and exposure to atmospheric agencies, with consequent leaching-out of the gypsum and oxidation of the ferrous compounds, would bring about a complete change in the nature and appearance of these rocks. If accompanied by pressure of overlying strata, the consequent collapse and degra- dation of a bed, such as D, would probably complete the obliteration of the already scanty traces of organic remains.

The anhydrite cores have now been lying in the open air for 24 years, and are cot~siderably weathered and pitted, the mineral first becoming chal~ged to gypsum and then dissolved away. In situ, however, the hydration seems to take place much more rapidly than the solutio~ of the gypsum. The result is that at the base the anhydrite mass was found more or less completely changed to gypsum for 4 or 5 feet. Both in this part, a1~d in the underlying gypsiferous limestones, some instructive features which seem to throw light on the present condition of the formation were observed. They can be well observed if the specimens are left under running water for some days, in order to remove the superfluous gypsum. The following may be mentioned :-- (I) Fragments from tlle lower part of the anhydrite-bed enclosing streaks of Magnesian Limestone. The anhvdrite is almost completely changed to gypsum throughout its mass. On the wea'thered surfacesglistening crystals of anhydrite are seen in layers or irregular masses standillg out from the more rapidly dissolviz~ggypsum, while the Magnesian Limestone is becoming liberated in soft, friable fragments taking on in part a yellow powder)" character, very different in appearance from the streaks of rock'in the undisturbed anhydrite above. If left in water r,themass disintegrates,throwing down the fragmentary Magnes!an'" Limestone. The coluplete removal of snlphates from a thick bed such as this suggests an origin for some of the irregular masses of soft comminuted breccia which are seen at various horizons in the Magnesian IJit~lestone. (2) ~lassesofbrecciated limestonerecemented with gypsum. The bvecciation of the Magnesian Limestone evidently begins before the complete removal of gypsum, and before the rock is chemically altered, no doubt through the strains set up in the mass of the formation. The hard, brittle,unfossiliferous rock (B) is found in part very much broken up into angular fragments of all sizes down to extremely minute powdery particles. The fragments are more or less displaced vertically aud are slightly separated, the intervening spaces being occupied by secondary gypsum cementing the otherwise un- disturbed brecciated fragments. After having been placed under running water for some time the mass becomes disintegrated. (3) Breceiated fragments of hard brown limestone associated with gypsum. Aggregates of dolomite crystals are seen on the surfaces of the fragments as the gypsum is dissolved away, aud also lying loose in the secondary gypsum. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

]90 ~lR. C. T. WRSCa~AXX O.n X .~IASS Or A.nHXDm~E [June I913,

Some details of the Warren Cement-Works boring were published in connexion with a paper dealing with the salt-beds of South- Eastern Durham, read before the Manchester Geological Society on June 5th, 1888.1 Mr. :Bird remarks upon the abnormal thickness of the anhydrite in this boring, and says: ' This may probably be the Lower Anhydrite of the Saliferous Beds, although the one foot of limestone above it is rather against the theory.' (Op. cir. p. 575.)

There seems to be no doubt that the limestone was merely a boulder near the base of the Glacial Clay.

I was for a long time of the opinion, which seems to have been the opinion of the borers also, that this anhydrite was an abnormal thickening of the Lower Anhydrite Series directly underlying the salt-beds, and supposed that its presence might be explained by the existence of a trough-fault having a north-westerly and south-easterly direction, and bringing that series down against the Upper Magnesian Limestone. Several facts, indeed, seemed to favour this view, which it is not necessary to recapitulate here; and, before the palseontological evidence furnished by the underlying limestones was forthcoming, the probabilities were about equally divided between the fault and the inclusion theories. Against the fault theory, the following reasons may be cited, which were kindly suggested to me by Prof. G. A. Lebour :-- (i) No bed of anhydrite or gypsum approaching a thickness of 265 feet is met with in the Red Beds overlying the Magnesian Limestone in Durham or ]~orth Yorkshire. I find that the greatest recorded thickness of the true Lower Anhvdrite of the Saliferous Series is 77 feet 6 inches at the West Hartlepool Cement-Works of 5[essrs. Casebourne ; while in the Seaton-Carew boring it was only 38 feet 7 inches thick. Taking into account the whole of the anhydrite-beds met with in these two borings: that is, the upper layer which is always met with overlying and protecting the salt, and the lower series of more variable thickness underlying the salt, together with a bed of red marl, presumably representing the salt absent here, the total thickness was lO_.4 feet 6 inches a~ West I-[artlei)ool and 54 feet 7 inches at Seaton Carew. (it) Among all widely-developed dolomitic rocks abroad, layers or Ienticles of gypsum or anhydrite, regular or irregular, and often of very great size and thickness, are common at many horizons, and by their solution and erosion have been repeatedly shown to be the cause ot" much internal deformation of the enclosing limestone, as well as of many ' slacks' and valleys at the surface. The phenomenon is very usual in connexion with the Trias in many parts of the Alps, where it has been called in to explain the features of certain high- level lakelets and valleys. So far as physical and chemical characteristics are concerned, the Triassic Alpine Dolomites are in many ways comparable with the Durhanl Permian Magnesian Limestones.

However, the presence of two genera of brachiopoda in the lime- stone underlying the anhydrite at Hartlepool must allocate it to some bed of the great middle fossiliferous division of the Magnesian

l W. J. Bird, Trans. Manchester Geol. Soc. col. xix (1888) p. 564. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

Vol. 69.1 IN T~v: ~tAGXasI~X LIM~SIO.X~.~ H~Z~POOT.. 191

Limestone. The experience of all workers in this formation in Durham is that brachiopods die out and disappear before tile deposition of any o[ the upper beds) We are, therefore, driven to the conclusion that the greater part of the Upper Magnesian Limestone Series, and apparently also a considerable portion of the middle beds, are here represented and replaced by an included mass of anhydrite of uncertain shape and size, occupying in its" present condition a strictly limited area in the Hartlepool district.

:Fig. 1 (p. 192) is an attempt to represent diagrammatically the boring through the anhydrite, and side by side with it the most reliable boring records obtainable in the immediate vicinity, with the view of showing the beds which are replaced by the anhydrite. The discrepancy in the limestone in the various borings will be noticed, and, indeed, the absence of any bed having anything like a stratigraphical continuity over an extended area is a marked feature of the Upper Magnesian Limestones in Durham. The boring near Hart Railway-Station is 2~ miles north-west of the Warren Cement-Works boring. The limestone was met, with at 37 feet below the surface and completely pierced. It had a thickness of 708 feet, from which fact and the outcropping of Upper Limestones not far away, one may reasonably infer that all the great divisions are represented. No fossils were recorded, and the cores are now lost. The boring at Howbeek is situated near the Hartlepool Union Workhouse, about a mile away from the anhydrite boring. The boring was still in limestone at 324 feet, and a good supply of water was obtained. At West Hartlepool Waterworks, whenever borings are sunk, a good supply of water is obtained, and constitutes the household water of the two towns. It has been supposed, though it is by no means certain, that the water is held up by the mass of impervious anhydrite a little to the eastward. South of the West Hartlepool fault a boring was sunk at the West Hartlepool Cement-Works (Casebourne's Boring). Under 30 feet of Glacial drift the red beds were encountered, having a thickness of 575 feet 6 inches, following which the Upper An- hydrite Series (18 feet 6 inches), red and blue marls representing the here-absent salt-bed (28 feet 6 inches), and the Lower Anhydrite Series (77 feet 6 inches thick), occur in descending order. Beneath this, the Magnesian Limestone with gypsum was met with at a depth of 730 feet from the surface, and was pierced to a depth of 40 feet, the total depth of the boring being 770 feet. The boring was not continued far enough into the limestone to show whether any extensive bed of anhydrite existed in it, and the cores having, by a great misfortune, been recently thrown into a pond and buried up, I was unable to examine them for fossils. This feature seems to be common to the Upper Limestones over the whole of ~North-Western Europe. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

[ 192 ] Fig. 1.--Vertical sections of borings in the Hartle_pool area. HART. 2

WEST WARREN HARTLEPOOL CESIENT PL~LP WORKS. WORKS. 7 Yellow 3 Limestone Sea ~ ie-V~ 54' 3"

53 t Yellow I~imestone, broken. 32v Dark Pinnel / ~'ellow LimestoneI and Cobbles. Yellowish 3 8` ; C av~Bouldt Yellow sol ~uvv~m: I Yellow Limestone, very much i Magnesian broken, l Limestone,

86, 7,p x4~'

Yellow Limestone. 55' 9" Anhydrite Soft Yellow Dark Yellow Limestone. 265' 7" Limestone. 4z I 23 p xx~ 1.7 miles 1-6 miles

Very Hard Yellow. 2oP4~]

"Yello , Very Hard, ,imest ne Yellow and Grey JointT Limestone.

~"eZ Grey .mestol :. *2 .lght ( 'ey Limest, ,e. -- G~p~-~,~r--= 23 r Dark Grey Yello Limestone. mestol ,. x.I

.=I Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

Vol. 69. j AI~HYDRITE-MAS$ Il~ THE :MAGNESIAN LIMESTONE. 193

III. Bom~os ix THE ~AGBTESIAN LIMESTONE WHERE IT IS PROTECTED BY RED BEDS. The great boring at Seaton Carew was described in detail by E. Wilson, 1 who stated that no ibssils were detected in the cores, so that no opinion can be ibrmed as to the horizon of the lime- stones met with. The limestone here occurs nearly 200 feet higher up than at West Hartlepool Cement-Works, and probably has a northward dip. The section is important in connexion with the present paper, as revealing a mass of 'anhydrite with beds of dark-blue shale and gypsum,' 35 feet thick, at a depth of 84 feet from the top of the Magnesian Limestone, which here attains the greatest recorded thickness of 878 feet. It is note- worthy chat the limestone is gypsiferous throughout this great thickness. A critical examination of this boring, so far as the details recorded may be reliable, shows the aggregato proportions of the formation to be as follows :- Sulphate-free limestone ...... 480 Limestone impregnated with gypsum and anhydrite ...... 358 Pure anhydride and gypsum ...... 35 At 140 feet from the bottom of the limestone is a thickness of 260 feet of limestone free from gypsum, which might correspond to part of the Shell-Limestone, but no fossils are recorded. I have very little doubt that they would have been found, if a search had been made. With this boring another may be contrasted : namely, that sunk at Whitehouse Farm near Norton in 1892,: about 7 miles south- west of the Seaton-Carew boring, where the thinnest recorded complete section of the Magnesian Limestone occurred, measuring only 299 feet in thickness. No fossils are recorded. Whichever division of the formation may be represented by this rock, the fact of importance in connexion with this discussion is the presence of large interstratified beds of anhydrite and gypsum, having an aggregate thickness of 84 feet. They commence about 85 feet from the top of the Magnesian Limestone, the most considerable individual bed being 37 feet thick. The sulphate-free rock in this boring has an aggregate thickness of about 160 feet, while the beds of limestone impregnated with anhydrite and gypsum aggregate about 56 feet.

The presence of large quantities of anhydrite and gypsum in the Magnesian Limestone is a usual feature wherever that formatiorL is covered by a protective layer of comparatively impervious material as in South Durham, and undoubtedly represents a more original and unaltered condition of the formation. This fact encourages the idea that the mass of anhydrite beneath

1 Q. j. G. S. vol. xliv (1888) p. 781. "- T. Tate, ibid. vol. xlviii (1892) p. 488. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

194 ~. c. T. Tt{ECH]IANN ON A ,MASS OF ANHYDRITE LJune ~913,

]tartlepool Harbour occupied laterally a very much more extended area when it was originally deposited; also that it has been gradually reduced in size, and represents in fact the last remnant of anhydrite formerly common to the whole formation, its great r size and thickness havi.g saved it from complete removal 9 One of the objects of this paper is to demonstrate that most of the changes and vicissitudes undergone by the Magnesian Limestone are due to the sub- sequent removal of sulphates from the formation. These sul- phates were origi.ally present, both as interstratified beds and lenticles, and also impregnating and in very close association with tile limestone, and their II removal brought abouta collapse, degradation, and settling-down of great parts of the formation. The most obvious result of

-51 _ '.2 this proeess is the brecciation and internal deformation which are such common features of the ' z .-~ rock. The less obvious changes r 9,,a v-~ are those resulting from the removal o[ sulphates closely in- corporated with the mass of the %~ I 5 rock, leading to a molecular ~ ~ ~ : .- degradation with consequent ~ ~ segregation, and other processes which bring about a more or less complete obliteration of the m m z fossils. .... The solution-breccias des- cribed in the present paper frequently simulate effects which might have been anticipated if the Permian rocks had been 121 m e subjected to horizontally-acting dynamic forces 9 While not pre- ~ ', suming to deny the possible existe.ce of such forces, I have seen nothing in the southern part of Durham which would lead me to suppose that the disturbances in the Magnesian Limestone were due to causes other than the effects of solution herein described. The brecciation is confined to the Magnesian Limestone. In Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

Vol. 69. ] IN THE MAG~'ESIA~ LIMESTONE AT HARTLEP00L. 195

Blackhall Sinking the thin bed of Marl-Slate together with the Yellow Sands were to all appearances undisturbed and in normat condition, in striking contrast with the great mass of deformed carbonates lying above. Slickensided surfaces have been noticed in several instances. The)' occur between the masses of Shell-Limestone conglomerate at Blackhall Rocks, and can be seen on a small scale in the brecciated gypsiferous limestone beneath the anhydrite-mass at :Hartlepool, where the gypsum seems to have acted as a lubricant ; but these instances are purely local, and are such as might have been produced by movements set up in the mass of the rock through reduction in volume by solution. Whether the more extended movements which have recently been described ~ from the Sunderland area are due to the same or to independent causes must be left as an open question for the present. The discrepancy between the thickness of the protected limestone at Seaton Carew (878 feet) and that of typical sections of the unprotected ibrmation north of the fault which include all the divisions (Blackhall Sinking~688 feet, ]=[art Boring~708 feet), would seem to point to a very considerable reduction in volume on removal of the sulphates ; though it would appear to be necessary to hold this view with reserve, owing to the possibility of the fault having been active in Permian times.

IV. THr, FOR)IER PRESEI~eE OF SOLUBLE CO.N'STITUEI~TS IN TltE MAGXESIA~ LIMESTO,-'gE. The former presence of soluble constituents, presumably sulphates, can be inferred from several features observable in the formation in this and other areas. (1) The intense porosity of many beds, both in the Upper and in the Middle Limestones, which, from the existence of plentiful casts of fossils, are shown to be practically unaltered in volume. The highly magnesian character of these beds further indicates their original condition. (2) The presence of hollow or negative cavities or spaces left by crystals or aggregates of crystalline material in man) beds. They are most apparent in the well-stratified, unfossiliferous beds of the middle division, overlying, or otherwise associated with, the Upper Shell-Limestones ; but I have also found them sparsely distributed in some of the fossiliferous beds. When very numerous, causing the rock to become extremely porous, they lead in some cases to a structural collapse with development of the usual hard, calcareous, segregated breceias. When replaced by calcite, the crystalline aggregates appear as stellate structures on broken surfaces. L D. Woolaeott, 'Stratigraphy & Tectonics of the Permian of Durham (Northern Area)' Q.J.G. 5. ,'~L lxvii (1911) pp. 312-1:3. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

196 xtR. c. T. TR~CH~tAm~ O.W A UASS Or ~nYDm~E [June I9t3,

In some thinly-bedded limestones they are arranged in layers on the planes o~ bedding, as though some crystalline substance had been thrown down rapidly from a concentrating solution as formless plates and aggregates on the sea-bed, to become covered up by the next layer of sediment, and only to be removed again by solution long after the solidification of the deposit. I find that the rock which encloses these structures is always of a highly magnesian character (45 per cent. of magnesium carbonate). These structures can be compared with crystals of anhydrite that occur in several pieces of unaltered Magnesian Limestone in the lower part of the anhydrite-bed at Hartlepool. In this case the pieces have been cut through by the boring-tool, giving a surface which has been exposed to the atmosphere for 24 years. The anhydrite has been changed to gypsum and dissolved away, the result being a fretted surface of limestone with stellate spaces similar to, but generally on a smaller scale than, those in the Magnesian Limestone at the outcrops. Stellar aggregates of gypsum are seen in masses of that material dredged from ItartIepool Harbour. They are obscure structures, and may be pseudomorphic after anhvdrite. J. W. Kirkby 1 refers to the pitted surface of several of the limestones of the Brotherton Beds and small-grained dolomites o~ South Yorkshire, which seems to be an analogous structure; and makes some remarks upon the curious false bedding of parts of the Magnesian Limestone. He doubtfully refers the former structures to ' some peculiar concretionary action, analogous to that which gave the Upper Limestone of Durham its remarkable structures.' (Op. cir. p. 291.) (3) The apparent former presence of lenticular inclusions of soluble substance. This is well seen in some of the thinly-bedded limestones of the Upper Middle Division, exposed on the shore south of Blackball l~ocks. In the cliff-section, the strata present a series of undulations, and are very loosely compacted along the planes of bedding. On the foreshore, however, the beds are seen in the form of low irregular domes'-' of more or less circular outline, measuring as much as 10 feet in diameter. Se~'eral examples are broken into by the sea, and present every appearance of having enclosed a lenticular mass of some easily-removed material, either powdery limestone or some soluble constituent. J.W. Kirkby ~ notices that in the flaggy limestones of the Brotherton Beds of South Yorkshire ' the surface-planes are generally a little apart.'

Whether the sulphates i,~ the Magnesian Limestone were originally all deposited as anhydrite, or partly as gypsum, is not precisely an easy question to decide. The evidence seems to be in favour of complete anhydrite deposition, such as might be expected in a sea charged with magnesian salts. 1 Q. g. G. S. voI. xvii (1861) p. 290. 2 This feature was first noticed by my friend, Mr. G. T. McKay, M.Sz. a Op. jam cir. pp. 289-90. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

u 69. j IN ThE MAGNESIAN LIMESTONE AT HARTLEPOOL. 197

The Hartlepool boring shows that hydration takes place more rapidly than solution of the gypsum, and therefore the expansion following upon the hydration of the anhydrite might cause much of the very curious internal deformation and crumpling on a small scale seen in many of the thinly-bedded limestones; this would probably be followed by a collapse and movement in the opposite direction on solution of the gypsum. All the samples of normal 'unprotected' Magnesian Limestone that I have analysed contain a small quantity of sulphur; but in no case does it exceed 0"2 per cent. of sulphur trioxide within my experience, nor have I yet determined its state of combination in the rock. The changes consequent upon the unstable solubility-equilibrium of dolomitic carbonates are very apparent in certain beds of the Magnesian Limestone. There can be no doubt that the intensely porous condition in which many of the beds are left after removal of the sulphates lays them open to these changes; a fact which should never be ignored in studying the endless forms of segregation and brecciation that this formation affords. The changes may be conveniently indicated by the following synopsis :-

Calcareous Constituent, Original l~ock. Magnesian Constituent. Hard, skeletal, spongy, cal-') Normal, bedded,fine- ~Yellow powdery material, 1 careous structures, ultimately I grainedlimestones | present as irregular len- coalescing into beds of dull, t or " roestones.' ~ ticles or pockets. lustreless, crystalline, massive ] Often intensely I Frequently containing rock of saccharoidal structure I porous and friable. [ (lust)" cavities or calcite- and all shades of colour, ~Magnesium carbon-~ lined geodes. (Contrac- (white, brown, bright yellow,] ate 40 to 4,5 per I (ion eflbcts ?) ashen-grey, etc.). 1 cent. ] Magnesium carbonate up- Magnesium carbonate 0 to 10 t Fossils traceable if ] proaching 46 per cent. per cent. I originally present. I Fossils obliterated in the Fossils always obliterated. J (. final state. The powdery magnesian constituent occurs in all stages of asso- ciation with, or complete rejection by, the calcareous segregations, the result being an endless variation both in appearance and in composition of the rock-mass. In all fossiliferous sections it can be observed that, in proportion as the segregation of calcareous structures becomes more apparent, the obliteration of the fossils becomes more complete. The beds chiefly thus altered prove to be the eastern and western equivalents of the Shell-Limestone, together with certain beds of the Upper Limestones--that is, limestones which on other considerations are shown to have been originally rich in sulphates. The Shell-Limestone, for reasons indicated in w V of this paper, is very much less affected; but the change is by no means absent, especially in the upper beds of that division. Siliceous residues are generally identical in character in the various stages of such altered rocks, though I have frequently 1 Generally described as ' marl' or ' marly limestones,' a too-often repeated error. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

198 atl~. c. T. TI~ECHMANN ON A MASS OF AI~ttYDRITE Effune 1913, found them less concentrated in the calcareous segregations, with subsequent idiomorphic growths round the quartz-grains. Patches or beds of original unsegregated rock occur ill several sections of these highly-altered rocks, frequently of very limited extent and irregular shape. As a]ready stated, they are generally of an intensely porous and friable nature and considerably fractured. The fossils are obtained only by carefully breaking the fragments along the original bedding-planes. These unaltered parts of the formation afford a useful clue to the original nature and palmontologieal horizon of several highly-altered limestones. ~ The above-described segregation is quite distinct from the typical eoneretionary structure or' the lower beds of the Upper Limestones. Both the botryoidal bodies and their investing matrix yield a great quantity of oily and carbonaceous matter on solution in acid: a feature not so evident in the former segregations, and one which would seem to suggest the formation of these bodies under the influence of organic matter. From analogies in quantity of organic matter, nature of residues, and general preservation of fossils, I am inclined to attribute the ' cannon-ball' structures to the action of segregation at a very much earlier period of the formation, anterior to the great changes undergone by the rock. The action of percolating water in leaching out the soluble con- stituents originally deposited with the Magnesian Limestone has already been noticed. The part which it plays in the dedolomiti- zation of great tracts of the formation through the removal, in great part mechanical, of the powdery magnesian constituent has also been touched upon. The Upper Shell-Limestones are in places considerably altered by the action of water, which percolates with particular ease through these rocks. ]11 Blackha!l Colliery Sinking, at one time in 1911, as much as 15,000 gallons per minute were being pumped from the Shell-Limestones. Analysis of this water showed it to correspond to sea-water diluted to about five times its volume with water containing calcium carbonate in solution. Previous analyses had shown that the proportion of sea-water varied at different levels. The effect is very noticeable in the so-called' interbedded con- glomerate' of :Howse, which seems to occupy a fairly definite horizon in the Upper Shell-Limestones. The rounded fragments are interbedded among layers of bedded limestone, and appear to have formed the hard unaltered cores in a soft and friable mass of limestone undergoing gradual change, the soft powdery portion having been removed by water. Each mass at Blaekhall Rocks and elsewhere is generally surrounded by thin concentric layers of altered material, which must be broken away to reach the fossiliferous rock inside. i R. Howse, 'Guide to the Collections of Local Fossils in the Hancock Museum,' ]889, p. 10, records a fragment of a coniferous plant from laminated mass in concretionary rock near V,'estoe. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

~r 69.] IN TttE M:tGNESIANLI.~IEs'roxE AT HARTLEPOOL. 199

V. ~-~ATUREOF THE StIELL-LIMESTONE A.ND THE .hkSSOCIATED STRATA. One of the most conspicuous features of the Permian of Durham is the ridge or bank of raore or less regular, dome-shaped masses of Shell-Limestone which lie in a belt from 2 to 4 miles wide in a north-westerly and south-easterly direction. Commencing with a fragment on Tynemouth Cliff, it occurs north of the Wear at Down Hill and Hylton Castle, passes by Claxheugh Rock and Pallion, t[umbledon and Tunstall Hills, Ryhope, Dalton-le-Dale, ]~awthoru, Beacon Hill, Easington Colliery, Horden, and Castle- :Eden Dene, until it touches the coast at Blaekhall l~oeks; after this it reappears ill Hesleden Dene, and thence presumably passes under ttartlepooh The presence of these masses of Shell-Limestone and the condition of the beds upon their eastern flank have been the determining factor in the nature of the coast-section between Sunderland and Hartlepool. The Shell-Limestones of the .Middle Magnesian Limestone form an irregular chain of reef-knolls, lying in a band more or less parallel with the old Pennine shore-line. They are the chief repository of the fossils of the Magnesian Limestone, the classical localities being Humbledon and Tunstall Hills, both south of Sunderland. Tim most probable view of the origin of these bryozoonal reefs would seem to be that they represent areas of comparatively sulphate-free deposition in the Permian sea, where the fauna, in consequence of greater purity of the water, would congregate and thrive. Assuming this, then, to be the true explanation, it will be seen that this rock, owing to its greater freedom from more soluble constituents, is to-day practically unaltered in volume; while the surrounding strata, more particularly the equivalents of the Shell- Limestone. upon its eastern flank, haw undergone structural col- lapse and degradation, leaving the Shell-Limestone as the elewted ridge or'bank which forms so conspicuous a feature of the geology of the county. This supposition, the plausibility of which can hardly be denied, in view of the already demonstrated replacement of Magnesian Limestone by sulphates in the Hartlepool area, certainly affords a ready explanation of many extremely puzzling features observable at various points on the coast-line where beds of Upper Limestone are brought down against, and frequently occur on a lower level than, the bank of Shell-Limestone. The strata on the western and eastern sides of the ridge of Shell- Limestone in the southern area of the county, that is, on the side facing the Pennine shore-line and on the off-shore side of the Shell- Limestone reefs, are markedly different one from the other. In the northern area of the county the western escarpment of the Shell-Limestone occurs directly upon the Lower Limestone, and generally only a short distance to the east of the great main Permian escarpment. Q. J. G. S. No. 274. P Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

In the southern area, roughly south of a line drawn from about Dalton-le-dale to ]=[etton, the Shell-Limestone rapidly passes westwards into a series of well-stratified beds, often profoundly altered, but not so completely collapsed and brecciated as are the equivalent beds on the eastern side. In the area under discussion the passage is r well seen in Castle-Eden Done, where at several points the beds are comparatively unaltered, and yield a scanty but character- no istic fauna sufficient to fix their Middle Limestone horizon. ~ They cover a very con- siderable area of country in the southern half of the count)-. Ill the northern area both these beds and the uppermost Shell- ,r Limestones are wanting, presumably through denudation. It will be seen then, that q~ despite the greater poverty of exposures, the Permian succession is moro complete in the southern than in the northern part of the county. (See fig. 3.) % The Upper Limestones have not hitherto o" been recognized upon the western side of the ridge; on the eastern side, however, matters are different. Here we find the various members of the Upper Limestones both overlying and flanking the side of the Shell-Limestone, which in elevated visible

.d sections slopes very rapidly down to the L) sea-coast, corresponding to the original eastern side of the reef. % Whether or no the Upper Limestones were ever deposited west of the Shell-Lime- stone reef is still an open question. In I-Iesleden Dene and at :Blackhall Colliery, for instance, and presumably at ]:[artlepool~ %) they certainly overlie the Shell-Limestone ; but a common position for them, especially evident in the shore-sections, is down

q5 upon the eastern side of the bank of Shell- Limestone. e~ The Upper Limestones may, of course, have been deposited in part upon the flanks of an elevated ridge or reef of Shell-Lime- I stone, in which case one might reasonably r expect to find derived fossils of the Shell- eb Limestone included in the Upper beds. :No fossils havo yet occurred to my knowledge in the highly-altered Middle Limestones on I A list of the fossils found in these beds is tabu- lated in the last column on p. ~ The most interesting form is Astarte va/li~;~eriana King, hitherto recorded only from the Lower Limeston~ at ~Vhitbv. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

Vol. 69.] ANttYDRITE-.MASS IN THE MAGNESIAN LIMESTONE. 201 the eastern side; but the Concretionary Series and the overlying ]:[artlepool or Roker Beds are, of course, full in places of their scanty but characteristic fauna. In my opinion ~ part of the Upper Limestones owe their present position on the side of, and at a much lower level, than the Shell-Limestone, to an irregular series of slip-faults caused by the degradation of the underlying, originally sulphate-bearing equivalents of the Middle Series. As a general rule, therefore, in the southern part of the count)', where the Shell-Limestone retreats from the shore-line or passes beneath the surface, the Upper Limestones are exposed in the shore-section. Where the Shell-Limestone approaches the shore or forms a high elevation immediately behind the coast, the shore- line and cliff-section are occupied by the highly-brecciated but well-bedded Middle Limestones occupying the lower flanks of the Shell-Limestone on its eastern side. These beds constitute large stretches of the cliff-section to the north of the area at present under discussion, and in general both these and the Upper Lime- stones dip rapidly away eastwards from the Shell-Limestone. The extreme complexity of parts of the Durham coast-section will, therefore, be readily realized. The typical Shell-Limestone is in general a hard, fine-grained magnesian rock, usually without very definite planes of bedding except in its upper parts, but is easily recognizable by its organic remains. The accumulation of certain forms of marine life in the Shell- Limestone may have been induced by the action of currents in the :Permian Sea, with consequent increase in the rapidity, and change in the character, of the sedimentation. Whatever may have been the inducing cause or causes, however, it is a true reef accumula- tion, the reef builders in this case being predominantly bryozoa (taking the place of corals), brachiopods, lamellibranchs, gasteropods, ostracods, and, in the lower beds, crinoids.

1 This is not mere conjecture. The faults which bring down the concre- t ionary beds against the Shell-Limestone north aTld south of Blackhall Rocks are of this order. At Beacon Hill, a knoll of Shell-Limestone facing the coast immediately south of Hawthorn Dene, the brecciated beds now lie in a sort of platform at the base of the hill, and form the whole of the cliff-section. A fissure in the breccia contains fallen masses of Upper fetid and fossiliferous Limestones of the concretionary series. The whole mass now occupies a lower level than the Shell-Limestone, with a fa,ma placing it about the middle of the Shell-Lime- stone and including Prodactus horridus. This rock is well exposed in a cutting for the new Coast Railway, which runs at the foot of the hill upon the platform of breccia. Part of the side of the Shell-Limestone reef has been stripped off in the railway-cutting, and slickensided surfaces are seen on the bank of Shell- Limestone passing vertically down the slope, indicating the downward movement of beds formerly adjacent to the now bared slope of Shell-Limestone. The Middle Breccias in the cliff are n'uch segregated and unfossiliferous. Beacon ]:Jill, therefore, represents the original eastern slope of the anefent Permian reef, and is one of the best sections of Shell-Limestone at present exposed. :k quarry at the top of the hill shows a bedded Upper Shell- Limestone with a typically impoverished fauna. P2 Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

202 ~a. c. T. TI~,ECHMANNON A ~ASS OF A:N~YDRITE [June I9I 3,

There appears to have been a comparatively rapid though tranquil accumulation of remains of these organisms. The delicate hollow spines of Strophalosia and Product~s are preserved intact, and the valves of lamellibranchs throughout the bhell-Limestone are in most cases still articulated by the ligament, and separated merely to the extent naturally resulting from the decay of the animal. The great~ accumulation of marine life indicated by the Shell- Limestone does not seem to have been adversely affected by the presence of magnesian salts. Every sample of the typical, un- segregated, often profusely fossiliferous rock, taken from all horizons, that I have analysed, shows a unifol~aly high percentage of magnesium carbonate, ranging generally from 40 to 45 per cent. :By whatever means the magnesia gained access to a rock such as the Shell-Limestone, or its equivalent beds on the eastern or western side, which, when unsegregated, show a similar compo- sition, its presence is undoubtedly an original and contemporaneous feature of the formation. The phases of the LTpper Shell-Limestone exposed in the Hartlepool area may be tabulated as follows, in descending order, with their visible thickness in each section and the most obvious faunal features. The sequence must not be taken as a constant one, as the Upper Shell-Limestones probably thicken southwards :--

Shell-Limestones exposed in the Hartlepool Area. Thiekness in feet. Fa nna I Features. Brachiopod species, 2. Uppermost Beddecl Shell- Stropl~alosia very rare. Limestones. i 60 ! Intense dwarfing of fauna. Gastero- (Upper end of Hesleden poda, Bakerellia antiqua, and Dene.) ..J I Epithyris very common but dwarfed ~_ and variable. (" Brachiopod species, 3. Shell-Limestones With inter-'~ I Strophalosia rare. bedded Conglomerates. [. Typical middle forms very dwarfed. (Blackhall Rocks and lower { ,tO-~ ~E2pitht/ris common, but localized. end of Hesleden Dene.) .J Baketiellia erratotohaya very I... comnloll. Bryozoonal Shell-Limestones.'~ ~" Brachiopod species, 4. i Dwarfing less apparent. 8trophalosla (Castle-Eden Dene; Ivy- ~ 80 very common. Bryozoa as reef- Rock section.) J ~. builders. Bryozoonal Shell-Limestones.'~ ~" Brachiopod species, 6. (Castle-Eden Dent; ~ 20 Camarophoria scMotheimi and Tri. Deneholme section.) J I~ yo~wtreta multi2olicata appear.

In Blackhall-Colliery Sinking the full thickness of Shell-Lime- stone (about 335 feet) was encountered, and proved to exist beneath the surface in the district. The upper part of the Shell-Limestone, which alone occurs in the outcrops in the area under consideration, with its impoverished and dwarfed fauna, was clearly indicated as overlying the typical highly-fossiliferous rock, with profusion of brachiopods and other Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

Vol. 69. ] IS T~E ~tXO:~ESlA~ T.m~.STOX~. A~ HAR~L~POOr.. 203 forms, which is so characteristic of the northern area of the county. This upper or P,.oductus-free phase, so far as I could ascertain, had a thickness of about 150 feet in Blackhall Sinking. The fauna of the uppermost Shell-Limestones approaches in character that of the brachiopod-free Upper Limestones. It is characterized by (a) the comparative absence of brachiopoda, (b) the abnormal dwarfing of many typical Shell-Limestone forms, (c) the numerical profusion of certain genera which are charac- teristic of the Upper Limestones (T,o.bo and other small gastero- poda, Myalina, ,Schizodus, etc.). The increasingly unfavourable conditions that prevailed towards the top of the Shell-Limestone bring about the gradual extinction of all the typical brachiopod genera, except E2~ithyris and Stro2lmlosia (many of the largest and most conspicuous forms, such as Spirifer alatus and Atl, y,'is pectinifera, being the first to disappear, followed shortly by l~rodt~ctus and the large Camaroplwrice). The more adaptable lamellibranehs persist, though many in a dwarfed con- dition. Pleurophor~,s survives the ordeal, although dwarfed to about a third of its normal size, and persists throughout the Upper Limestones. The gasteropod genus Turbo is comparatively un- affected, as its great numerical abundance in some beds in Hesledcn Dene and at Blackhall Rocks testifies. The profusion of small littorinoid gasteropods and mytiloid lamellibranchs might be considered as evidence of influence of littoral conditions in the upper beds of the Shell-Limestone. The beds of small gasteropoda may be taken as evidence of shallowing water over the reef, ~ but neither the composition of the rock which maintains its uniform highly magnesian character, nor any increase in the insohlble residue, indicate any change from the conditions prevailing in the typical lower beds of the Shell- Limestone. The reason for the decadence of the fauna is more probably to be sought in the increasing amount of sulphates in the sedimenta- tion, following upon the gradual failure of the conditions which gave rise to the formation of the Shell-Limestone. This view seems to be further favoured by the great amount of bedding (regular and irregular) and internal deformation, at present observable in all sections in the Upper Shell-Limestones in the district, as also the association with them of unfossiliferous beds containing the cavities, presumably left by sulphates, already described.

VI. TYPICAL SECTIONS A~ND EXPOSURES IN THE ]~ARTLEP00L AREA. (1) Hartlepool Foreshore. The cliff-section is now greatly obscured by the sea-walls, but the main succession may be studied and Upper-Limestone fossils collected at various points at low tide. J. W. Kirkby, Q. ft. G. S. vol. xiii (1857) p. 218. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

204 ~l~. c. T. ~arzcn~A.~ o.~- x xfass OF A~-~D~ITr. [June I9I 3,

Tit iekness i~t feet. f" Soft, white, porous, fi'iable, well-'] bedded limestones, showing [ dendritic specks ou fractured ~ 30 (Schiz~ schlotheimi Gein. sm'faces. Calcite-lined geodes I" ?. _llytilus sefltifer King. 1 and small brown fluorites { occur ...... j Massive bedded ' roestone' in part`] H~a~ssr I of section, enclosing large ~_ Li~Es~o~-Es..~ flattened lenticles of powdery ~ 20 No fossils. HARTLEPOOL material ...... , SERIES. Variable, hard aud soft. white~ (Schizodus schlotheimi Gein. and yellow limestones. "Fossils [ / Pleurophorus costatus Brown. generally obliterated, lint some [..~ M,/tilus septifer King. occur in the harder parts of the ( 35 Tz'o'bohelicinus Schl. rock west of the new break- I [ Nation cf. leibnitziana King. Small indeterminate gastero- (. water...... j (_ poda.

At Brunswick Brewery, tIartlepool, a boring was sunk to 100 feet in the limestone ; but no trace of anhydrite or gypsum was met with. In Victoria Dock the limestone was struck on the east side of the dock, at a depth varying between 14 and 23 feet beneath Boulder Clay; but on the west side, 350 to 400 feet westwards, the depth had increased to 36 and 50 feet. This is apparently not the dip of the beds, but represents the westward slope of the old pre-Glacial 'slack' or valley of which the anhydrite-mass forms the floor.

(2) West Hartlepool. Limestone of this outcrop is well exposed in a quarry near the waterworks, and in the railway-cutting oft the east. The following section may be seen in the quarry :~

Thickness in feet. Fauna. (Thin, well-bedded layers of soft,-~ yellow, decayed, extremely t porous limestones, interbedded with hard bands a few inches HIOH~ST thick. A.~sociated with these I Seh izodus schlotheimi Gein. L ] are several beds' 1 t~ 2 feeti30 Mqtilus septifer King. I~ESXOS]~s. thick, of a soft yellow rock P'leu~'oph~'us costatus Brown. showing a granular oolitic I structure. Traces of fossils are abundaut in some bal~ds, L. but are nearly obliterated ...... J

A boring at the waterworks shows that these beds continue to a depth of 39 feet from the bottom of the quarry, when an extremely hard limestone is met with, having a thickness of 9 feet. Beneath this the details of the boring are unreliable, but it was carried to 69 feet without encountering any trace of anhydrite or gypsum. Samples of the above-mentioned limestone were i0und Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

u 69. 3 I~ THE MAGNESIAN LI,~IESTOh'E ),T HARTLEPOOL. 205

lying round the wells, but no fossils could be detected in them. The limestone is similar in appearance to the flaggy beds which underlie the Uppermost Limestones in the Hesleden-Dene section. It is a well-bedded brown and grey fissile rock of extreme hardness, containing nearly 43 per cent. of a fine siliceous residue.

(3 a) Blackball Rocks.

This is the only spot on the Durham coast where the true Shell- Limestone is exposed in the shore-section. The Shell-Limestone reef occurs only a short distance inland all the way down the coast from Sunderland to Hesleden Dene ; but the actual exposures of rock on the shore are either the Upper Limestones or the unfossiliferous breccias which occupy the eastern flank of the Shell-Limestone. The section is as follows :--

Thickness in feet. Fauna. Dusty, porou% decayed lime--] stones. Generally ~vell-1)edded| and oceasional]'r massive. Much collapseci. Hollow ~'~ aa,~ No ~bssil~. pseudomorphic aggregates after I sulphates plentiful in places ... J Peastone in part of the section ... 2 ,No fossils. Upper Shell-Limestone with inter- -' ]~PPE R [ stratified conglomerates. Large and small irregular rounded [Dwarfed and impoverished masses of variable hardness. i Shell.Limestone fauna, l In parts apparently piled to- [ LI.~Esro~Es. I gether indiscriminately, in other i parts in distinctly stratified "40"~iA andbandOfotherSmallformsgaSteropodaoccurs order. Severalbandsof bedded [ locally about the middle of limestone appear between the '[. the conglomerate. layers of rounded fragment~. , Hard limestone showing much [. internal deformation ...... I~ase not seen. 1 Lists of these fossils are given ill tabular form ill w VII, p. 215.

The Middle Limestones are here exposed over a length of slightly under a mile of coast-line. Both north and south of this section the Upper Limestones are faulted down against the Middle Lime- stones , the incoming beds being in each case the Concretionary Series. The well-known caves at this place are due to the rounded masses of Shell-Limestone Conglomerate becoming detached by the action of the sea, and leaving the overlying bedded limestones as a roof to the caves. Southwards, the overlying beds occupy the cliff-section until the fault at Cross Gill is reached; but they change considerably Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

206 ~tR. C. x. zarC~t~x~'~r o~ A ~xss oF AXa~:DarxE [June 19I 3,

in character. Slightly north of the fault the following section occurs :-- Thiekness in feet. "Massive white limestone, assum-'~ ins a 'roestone' structure and I de~'eloping hard calcareous spongy 1)reccias for some dis- I U1,PZR tanee north of the thult. 1 Laver of small yellow brecciated ! ~lflDDLE fraffments, thi'nning out betbre ~ 60 No fossils. LI~ESTONI~S. the fault is reached. Thinly stl~tified limestone, very I loosely compacted, sh0wb~g [ traces of large lenticular in- t (. clusions now removed ...... J

Between the fault and the incoming Concretionary Series a well-defined space intervenes, filled with a soft collapsed mass of eomminuted white-and-yellow fragments of a fetid limestone. The bedding is visible in part, and a band of limestone at the base dips rapidly southwards; this seemingly indicates that the beds next encountered have been carried downwards.

(3 b) Coast-Section south of Blackhall Rocks. The coast-line between Cross Gill and the Targets at :Hart is occupied by the lower series of the Upper Limestones, here forming two divisions, of which only the lower shows any concretionary structure. In no case is that structure developed to the extent observed in the Sunderland area. The section is as folIows :~

Thickness in feet. ~'a ~r 7. (Thinly - bedded, well- stratified ] yellow lime~tone~, frequently t ('Eilograna (?) Termia~a2 t)recciated and collapsed. Fos- I I King. sils occur lying on a matted ~35~ Sehizodus sehlotheimi Gein. I ground of rods of .Filograna. [ 3[ytilus septife~" King. Sections of this fossil arc ~_Natica sp. visible in the face of the cliff' as CO~CR~rIol~ARY I small circular l)unctures ...... J J Hard, fissile, fetid, flashy lime. ] LI~ESXON~. stones with interstrat]tied beds l developing coucretionary, bo- [ ~-Schizodus sehlotheimi (h, iu. tryoidal, and camtou-ball struc- [ [ ~l~tilus septifer King. tures. Associated with these [.,~J Slabs of eoneretionary lime- (as matrix of the concretions) ~ov~ stona, with crowded masses are soft, fetid, grey or browll [ [ of testiferous specimens marly - looking i ~ limestones, I ~ occur. occasionally massive, generally [_ much brecciated and collapsed.._J Base not seen.

t Ineorreotly described by earl:r writers as' marl' or 'marly limest,~ne.' It yields practically no clayey re.cidue on solution, but much oily organic matter. W. King, ' Monogr. Perm. Foss. Engl.' (PaL Soc.) 1850, p. 56. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

Vol. 69. ] Ix THE ~t.~6,~ESI.tN LI.~IESTONE XT H.kRTLEPOOL. 207

(3 C) Coast-Section from Blaekhall Rocks to Castle-Eden Dene. This section measures slightly over a mile. The southern part embodies a section of the Concretionary Series similar to that already described. The fault that brings down the concretionary beds occurs a short distance north of Blaekhall Rocks. It is apparently of slightly greater throw than the corresponding fault on the south. The northern part of the section, across and beyond the mouth of Castle-Eden Dene, exposes the following beds :~ Th ickn ess in feet. Fauna. Very soft, white and yellow, powdery limestones, associated with a ' roestone' well seen on l I the shore. Both arc pierced UPPER,lOST I and interbanded with irregular L LIM'ESTON:ES. "{ masses of yellow, crystalline, }-25 (?) Schizodus sp. I calcareous material whicll re- I rains in part the 'roestone' I structure. The oolitic graiu~ 1 are filled with aggregates of l.. brown fluorite-crystals ...... j Owing to the complication of the cliff-section by glacial action and fallen sand and clay, it, is impossible to ascertain the thickness of either these or the concretionary beds.

(4) Hesleden Dene. A post-Glacial ravine extending in a more or less east-and-west direction for a distance of about 4 miles. The stream has cut a gorge in the limestone, laying bare a goocl and contiuuous section of the Middle and Upper Magnesian Limestones for about 3 miles. The limestone is first met with about half a mile from the dene mouth. :Between the two railway-viaducts which cross the dene, the stream passes through a gorge where the following section of Upper Shell-Limestone is exposed, and can be studied both in the gorge and in an old quarry in the dene close by :- Thickness in feet. Fauna. f-Hard, bedded, Shell-Limestones. "1 I Thinly-bedded limestone in part of the section. I I Interbedded , conglomerates [ Dwarfed and impoverishe,i UPPER rounded, or angular and much Shell - Limestone t'aulla Srrl~Lr.- -{ broken up. Themasses consist ~-35 similar to, lint scantier LIMsSZO~.S. ,1 Shell-Limestone.~typical, fine-grained, compact I than,Rocks.thatof Blackhall_ I Hard limestones, more or less[ bedded, showing locally much ~. internal deformation ...... J Prevailing dip of the beds = about 5 ~ east-south-eastwards. These beds very closely resemble the Shell-Limestone Con- glomerate of Blackball Rocks and are probably equivalent thereto. They very likely owe their existence here to a fault west of the gorge which cannot now be traced, but may lie beneath the railway- embankment. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

208 ata. e. T. ~ttECrL~A_~ OX X _~ASS OF .~Nrt~Dai~g [Juno I9I 3,

On crossing the railway one meets with the Uppermost Lime- stones (Hartlepool or Roker Series). The beds now dip more or Jess regularly eastwards and south-eastwards at a small but variable angle, so that older beds are encountered as one ascends the stream until finally the highest Shell-Limestones are met with at the upper end of the dene. Owing to the rapid lateral alteration of some of the beds, the sequence must not be regarded as a constant vertical section. The succession is as follows :- Thickness in feet. ~Fauua. f-White .limestones, well- bedded,] massive in part. Thinly bedded I (~Schizodus schlotheimi Gein. in the upper and lower parts. ~ 30 J3I!/tihts septlfer King. A massive bed, with much L "~ P'leurolM~orus eostatus Brown. eross-jointing, is quarried as a[ ~Natiea (?) sp. building-stone ...... ) HIGHEST Thin bed of ' roestone,' e~mlpri~ing'~ ][~IM ESTOI~'ES. large and small irregular len~- [ -~ ticle~. Very higlfly tbssili-( 4 Same as above. ~-~A-RTLEPOOL I ferous ...... i .... ) O1% Indurated and partly-~cgregated] ROKER wlfite limestone.% developing a I SERIES. porous and irregular breccia[ I in parts. Occasionally much ~ 25 Same as above. cross-jointed. The 'roestone' structure is maintained, de- J [~ spite induration ...... J "Well-bedded, thin, hard limef] ~tones, white and yelh)w, and ] slightly fetid. Soft at the top, where they are much broken up and cross-jointed. The lower I~. part consists of a fine-grained , 20 No fi)ssils. grey and yellow limestone with I cavitie% as a rule very thinly bedded. 9(Well seen near Temps Hole.) _3J (.~) Honeycomb breccia with powdery ~ 10 "EQUIVALENTS material ...... ) OF THE -~ Well-bedded, yellow, commilmted'~ 2 No fossils. (]ONCI~ETI ONAI%u breccia ...... ) SERIES. Spongy breccia, much broken ~ 10 up ...... ) Very regularly bedded, yellow-] limestones, consisting of coarse- grained, soft, yellow beds, occa- sionally much broken up and jointed, intercalated with bands 25 i~*o fossils. of thin, hard, yellow, fissile limestone. Massive in part, with a hard honeycomb breccia [ at the base ...... J Well-bedded, porous, partly mas- 6 { Bakeeellia ceratophaga and - sire limestones ...... small gasteropoda. Variable, hard and soft, more or] less bedded limestones show- / ing intense internal de~brma- I ~Very dwarfed and scanty Shell- UPPERMOST tion, with pockets of powdery I Limestone fauna. SH EL~- material enclosing portions of [ J~I MESTO.NES. hard, granular, porous, corn- 50 ~ Many fossils, especially in the paratively unaltered rock in [ lower part, where bands full stratified masses. Massive ~ of Epithgris and small honeycomb breccias developed [_ gasteropoda occur. locally ...... Base not seen. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

Vol. 69. ] I~ TaE ~.~,~NrsIx~ rL~IaSTO~'E x'r HXrtTL~rOOL. 239

There is apparently in Hesleden Dene a perfectly conformable passage, down from the Uppermost White Limestones to the Upper Shell-Limestone, without any trace of development of coneretionary structure. Neither the typical fossils nor any trace of Filo.cp.ana recur in the presumed equivalents of the Concretionary Series. The same applies to the Hardwick-Dene section. The Shell-Limestones are exposed for a distance of over a mile, coming in at Jackdaw Rock, at which point the overlying yellow fissile limestones dip sharply south-westwards at an angle of about 15 ~, and ending with the disappearance of the rock beneath Boulder Clay at the top of the dene. Overlying and partly replacing the Shell-Limestones is a series of soft, white, bedded limestones, very porous and friable, but occasionally massive, with dusty cavities arranged along the planes of bedding. They are often full of hollow cavities, presumably pseudomorphic after sulphates. These beds are excessively tumbled and collapsed in part, with development of calcareous ribs and irregular segregated breccias. From the nature of the fauna as well as from their position, the beds at the upper end of Hesleden Dene are regarded as the highest Shell-Limestone that occurs in the county of Durham. (5) Castle-Eden Dene. This is a ravine extending in a north-easterly and south-westerly direction for a distance of nearly 5 miles. The valley is of pre- Glacial origin, and upon the Boulder Clay that fills the pre-Glacial wash-out the present stream has been superimposed. The stream apparently coincides with the line of the pre-Glacial wash-out in only the last part of its course, and empties itself into the sea near the northern boundary of the original valley, which has a width of about a third of a mile. The result is that the stream has in places cut .~ very deep gorge ~nto the rock, exposing a fine and nearly continuous section in the Middle Magnesian Limestones for a distance of over 3 miles. The strata in the shore-section at the mouth of the dene, as already described, belong to the Uppermost Limestones, and are here probably faulted down against the bank of Shell-Limestone. The following section of Shell-Limestone is exposed near the entrance of the dene, between Deneholme and the railway-viaduct, in the bed and on the southern bank of the stream :- Thickness in feet. Fauna. Grey and yellow, crystalline, line- -~ grained limestol~es of variable hardness, passing locally into [ ~A highly bryozoonal lime- breccias of varying degree of [ | stone, with plentiful ostra- UPPER fineness, in ~:hich irregular [_ ! cods. SHELL- 20~ Rock largely made up of LIMESTOSE. pockets and masses of powdery ( it material occur, i I comminuted fragments of Fossils in all stages of preserva- (. various organisms. tion, from pe~ffect preservation 1. to complete obliteration ...... The Shell-Limestone is again finely exposed between the Garden- of-Eden Bridge and White Rock. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

210 ~R. C. T. TRECHMANN ON .,k ltl.kSS OF ANItYDRITE [June 1913,

Ag Craggy Bank a good exposure of very fossiliferous rock occurs on the south side of the stream, some distance up the bank. It is here broken up into large and small irregular angular fragments, which however are in undisturbed position. At Ivy Rock the following fine section is laid bare in an over- hanging cliff about 80 feet high, where the position of the above- mentioned angular breccia can be seen about the middle of the exposure :- Thickness in feet. ~'auna. (Hard, massive, varial)le, indurated "} ] beds, muchbroken up. Fossili- ~ 30 ~autilus at the base. ] ferous in places ...... I Highly - fossiliferous angular "~ 15 Highly brvozoonal limestone. ] breccia ...... ) I This passes gradually but rapidh-] UPPER down into a soft powdery mass, I Sa~L- -~ tnueh cross-jointed, enclosing l LIMESTONES. bands of harder material, in }-35 which the tbssils are still recog- [ nizable in the layers directly I underlying the breccia ...... ) Thin, stratified, soft, uncollapsed } {CastsofBakevelliaanticlua bed of porous limestone in tim 2 and small gasteropods. stream ...... The prevailing dip of the Shell-Limestones, about 5 ~ to 10 ~ east- wards, brings up the underlying soft powdery beds, until at White Rock they occupy the whole of the cliff on each side of the stream, giving a very conspicuous section as follows :~ Th iekn ess in feet. :Fauna. S~:IJ~- [Yellow and white powdery friable-) I limestone. LI_~tESTOXE t Lines of stratification distinctly I ~EROI~O "~ indicated by bands of harder ~80 All traces of fossils al)l)a- STRATIFIEDII~XO T~ and less altered, but still very rently obliterated. WESTER:,- porous, limestone, l I Section practic'dly homogeneous { EQVlVALEST. (. throughout ...... ] Passing downwards and westwards the beds become less altered, the white powdery rock merging gradually into a well-bedded fine- grained limestone. The intermediate phase is well seen in the cliff above the stream opposite Seven Chambers, where the powdery material, accompanied by some calcareous segregation, becomes subordinate to bands of unaltered reek containing fossils. Between this place and Gunner's Pool many fine sections of com- paratively unaltered bedded limestones are exposed, representing the equivalents of the Shell-Limestone ou the western side of the reef. At Devil's Bridge the following section is laid bare :~ Th iekuess in feet. Fauna. [Well stratified, fine-ffrained,thinly] bedded, lmrd, aad slightly-/btid ] limestones. Generally ahnost [Vermes, larnellibranehs, unaltered, though breeeiatiou I 1 and ostraeoda. ~IIDDL:g and segregation are present to a BEDDED -~ small extent. Strata often very 760~ LI~tESTO~ES. I much fractured at right angles| I' Bryozoa and brachlopods to the planes of bedding, l L entirely absent. Flattened hollow spaces (left 1)y sulphates ?) present in some of iL. the less altered portious ...... ) Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

Vol. 69. ] I~ THE MAGNESIAN LI.MESro.NE AT ItARTLEPOOL. 211

At Gunner's Pool and Bruce's Ladder the above-described beds have undergone much alteration, and calcareous segregated bands are seen intercalated with yellow powdery materiah The latter is very apparent at the top of the section, but lower down has been largely removed. The calcareous bands here coalesce, forming a typical honeycomb breccia merging downwards into a hard unyielding thick bed of limestone which offers an obstacle to the stream. The whole mass is pierced with vertical fissures in various directions, through one of which the water finds its way. The fine wall of rock at the base of which the stream emerges is the face of another fissure, and affords a good section of these much altered rocks. The whole gorge is one of great natural beauty, and in parts is thickly hung with ferns. Fossils are entirely obliterated. Beyond this section, towards the upper end of the dene, the beds are less altered. .Near an old quarry the following section is exposed in the side of the stream :~

Tlt ickness in feet. Fauna. ('Well-bedded, thin, yellow lilne-'~" ~IIDDLE I stones. Very highly fractured[ (AstartevallisnerianaKing. BEDDED -~ at right av.gles to the bedding. ~- 6 - LIMESTO.'(ES.| Collapsedin part, with 1)owdery [ ( Schizodus sp. (_ material ...... _)

(6) Hardwick Dene. This is a small, post-Glacial ravine passing in a north-and-south direction for slightly under a mile, and joining Castle-Eden Dene about half a mile from the sea. The stream has in places cut into the rock to a depth of 40 feet, exposing a good section of the Upper Limestones. The ravine rises rapidly, and the dip of the s~rata is very variable, but higher beds are encountered as one ascends the stream :~ Thickness in feet. :Fauna. (Soft, yellow, well-bedded,rotten~ Schizodus schlotheimi Gein. limestones, which enclose large, | 3Iqtilus septifer King. rounded,hard masses containing i Small gaster~poda. a few fossils ...... 30 Small-grained 'roestone,' partly UPPERMOST indm'ated ...... J No fossils. :LIMESTONES. Soft yeliow limestone, more 07" less ) (Sch izodus and Mgtilus abun- HARTLEPOOL collapsed and brecciated, es-[ 20~ d'mt in a less altered OR ROKER pecially in the lower part ...... ) f. band. SERIES. Hard honeycomb breccia. "~ 'Roestone,; very porous in the| lower beds. "Large and small,}-50 No fossils. flattened, irregular, lenticular ] bodies very apparent ...... J , Thinly-bedded, fissile, well strati--] (?) I fled,white and yellow limestones I EQUIVALENTS of marly appearance, much brec- I OF THE -~ ciated and powdery in places. ~- 30 :No fossils. Co.~-cRETIO~'XRX" [ These beds become extremely] SERIES. i wllite, porous and friable in[ ~_ part with dusty cavities ...... j (?) (tlard, angular, limestone-breccia,) S~ELL- ~ the masses embedded in yellow~ 20(?) No fossils seen. LIMESTONE. powdery material ...... ) Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

'212 )lR. c. T. TRECHMAB'N ON A MASS OF ANHYDI~ITE [June I9~3,.

(7) Hart Quarries. Nearly 2 miles to the west of the waterworks at West Hartle- pool, the land rises rather rapidly to the 200-foot contour-line which corresponds with an outcrop of limestone. It probably owes its presence here to a fault which cannot, however, be definitely located. The limestone is well exposed in three quarries on the west side of the road from Hart to West Hartlepool, in a quarry at Hart Windmill, and ill a largo quarry near ~'aiseberry, south-west of High Throston, about a mile from the Ward-Jackson Park at West Hartlepool. As the last-named section is the most typical, and the only one. where any traces of fossils seem to have been preserved, it is t-ere described :- Thickness in feet. Fauna. ~- Very hard, deuse, brown and ashen "~ grey, segregated limestones. ] lrregu]arlv bedded, but stratifi- 25 eatiou vel:y apparent, breceiatod ~ Fossils obliterated. (?) in places. Powdery constituent [ HIGRES:r -~ entirely removed. .3 LIMESTO.~ES. [ 'Roestone' in part of section. 6 :No fbssils. Extremely soft and fl'iable, well- bedded 9yellow limestones, slmw- ~ 6 { Sehizodus sp. ing ' roestone ' structure in 3l~tilus sp. [. places. Fossils found in these beds were in the last stages of oblitera- tion. The genera are recognizable, but specific determination is hardly possible. They would seem to justify the reference of the beds in all these quarries to the Uppermost Limestones, here protected from denudation by the overlying mass of segregated calcareous material. Similarly altered beds occupy a very considerable area of country on the west. The surface-contour of these beds is extremely variable, determined no doub~ by the different hardness of the calcareous and magnesian portions of the rock. Such rocks are exposed in quarries a(~ Wellfield, ~Vingate, Trim- don, Haswell, etc., where in most eases they can be shown on pal~eontologieal evidence to represent the western equivalent of the Shell-Limestones. A somewhat similar limestone is exposed in a quarry at Whelly Hill, near the intersection of the Durham, ~artlepool, and Stockton roads. It lies very slightly above the 400-foot contour :~ Thickness in feet. ~'auna. [-Collapsed, recemented calcareous fragments~ I forming a rather massive bed ...... ) 4 I Very thinly-bedded limestones, white and] (?) I yellow, showing great internal bending;] .-MIDDnE -~ towards the base the rock 1)ecomes spongy I Li~Esxo.~-~. I and associated with powdery material. ~30 ~ofossils. Hollow spaces left by sulphates are very I numerous, causing the collapse and breccia- / (_ tion of the overlying part ...... ~J Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

Vol. 69. ] I~ TRE MAGNESIAN LIMESTO~NE AT HARTLEPOOL, 213

(8) Blackhall-Colliery Sinking (1909-13). This sinking has been of great help in elucidating the structure of the district, and shows that the normal Permian successimt exists beneath the Upper and the Upper Middle beds exposed at the surface. It is situated almost midway between the typical exposures of Upper Shell-Limestone of Blackball Rocks and Castle-Eden Dene, and is probably the only sinking that pierces the whole thickness of the Shell-Limestone, though it is situated not on the centre, but near the eastern slope of the reef. Two shafts were sunk, the northern and the southern shaft, 165 fee~ apart. A drift to carry off the water was sunk between these and the sea, 210 feet east of the shafts, to a depth of 246 feet. The following section is drawn up, both from data which I obtained myself, and from examination of rock-samples taken from authenticated levels, in the possession of the Horden Collieries Company, Ltd. It represents the section in the southern shaft. The thicknesses given for the Upper Limestones are not absolutely certain. The total thickness of the Permian strata is 688 feet, and the depth of the base of the sand-bed from the surface is 756 feet.

Thickness in feet. Farina. Bouhler Clay...... 68 Broken limestone, similar to a } HIG~tEST bed exposed in the railwav- LIMESXO-~- { cutting near by. it has a roe- 19 No fossil~ seen. stone in part ...... COnCREXIOXXR'Z ~ Limestones with well-developed ~ (?) No fossils seen. LI~tEs~o~r~.s. ( concretionary structure ...... ) 63 SH,LL-UP~'~R {Shell-Limestones of ,'ariable'(155{Highly fossiliferous, buL LrMxsTo~E. character ...... ~ with a restricted fauna. t ~ ('Profusely fossiliferous. MxI~ [ ~ Fully developed fauna. SH~.LL- Typic'd Shell-Limestones ...... ~- 180 Masses of bryozoa at; LI~tZsxo~. [_ several levels. f- Yellow, bedded, friable limestones. ] Fragments of bryozoa an(t drifted plant-remains. I Brown fi'iahle limestone. White friMfle nodular limestone. I L0WXR Hard hrown and white bedded ~-240 No fossils seen. LIMESTONES. limestones. ] Very hard, brown, 1)anded lime- stones, with carbonaceous part- ings ...... J ( :Pal~eoniseus, Platysomus, MxRL- Compact dark.grey and black } ) Pygopterus, etc. with SLXIE. { shales ...... 5 ) coprolitic matt~r,~ Also, t. (.7) Posidonomya. I Sand-bed, very compact in parts, l YELLOW resembling a dark-~ey sand- 26 No fossils seen. SA~-I)S. stone-conglomerate. Enclosing pyrite in cracks and veins ...... Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

214 ~aa. c. T. TI~ECH~AXN ON :t ~SS OF AXnYDI~IIE [June 1913,

I am told that when the stratified beds at, the top of the Lower Limestones were encountered beneath the Shell-Limestone, the dip was found to be due south, at an angle of 16 ~ : and that, in con- sequence, these beds occurred 50 feet lower in tile southern than in the northern shaft. However, when the Marl Slate was reached in the tbrmer shaft, the dip was a very slight one to the south-east, whence we may infer that the disturbance of the upper part of the Lower Limestone was a local phenomenon.

In the drift, 210 feet east of tile shafts, beneath the Boulder Clay, an incoherent, soft, yellow limestone of marly appearance, showing no stratification, was encountered, and pierced to a depth of 246 feet. It exhibits a distinct ' roestone' structure in samples which I obtained. The best explanation that I can offer of this sudden ch~mge is that here we are off the reef of Shell-Limestone, and that this substance is part of the collapsed Upper Limestones occupying the eastern slope of the reef.

vii. Norms o~ xH~ PAL2F:ONTOLOG]7 OF THE ]{ARTLEPOOL AREA.

The changed conditions represented bv the Middle Limestones in the Durham area, while introducing at least thirty new species, gave the Lower Limestone fauna, so to speak, a new lease of life under the protection of the Shell-Limestone bryozoonal reefs. There is evidence to show that this sudden influx was never repeated, but that the fauna was caught and trapped in a sea isolated from the oceans. Its adverse fortunes and gradual de- cadence and extinction, following on the slow failure of the conditions which inaugurated it, can be studied as we ascend in the Shell-Limestones. Obviously, then, new species are hardly to be expected in the Upper Shell-Limestones, more especially as the material for the classical monographs was chiefly obtained from the highly fossil- iferous localities of the main Shell-Limestone then open in the" Sunderland area. Nevertheless, many of the typical forms described by King and others undergo considerable change as we ascend in the formation. Owing to the continued absence of a revision of the Anglo- German Permian fauna in the light of recently investigated marine Permian faunas, the lists of tbssils are somewhat unsatisfactory. To avoid any confusion, I have based my identifications for all forms, except the braehiopoda, on King's Permian Monograph (1850). For the brachiopoda I have made use of Davidson's ' Monograph of British Permian Braehiopoda ' (1857-62). Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

Vol. 69. ] L~ THE MAGNESIAN LIMESTONE AT HARTLEPOOL. 215

FOSSILS OF THE ~IDDLE ~AGNESIAN LIMESTONES IN THE HARTLEPOOL AREA~

SHOWING THE GRADUAL EXTINCTION OF THE FAUNA oF THE SHELL-

LIMESTONE.

[The last column includes the fossils of the bedded western equivalents of the Shell- Limestone in Castle-Eden Dene. r----rare ; e=common ; v.c.=very common.]

Lower Bryozoonal Shell- [-IighestlBedded Shell- Limestones of I Shell-Limestone Shell- [Middle Lime- Conglomerates. Lime-I Lime- stone. Castle-Eden Dene. NA~ES stones, stones.

OF .~

SPECIES.

o

Vermes. ~pirorbis permianus King '~ Serpula (?) pusilla Gein ...... ~" Vermilia obscura King ......

Anthozoa.

Petraia progeunda Germar ......

Bryozoa. Calamojoora maerothii Gein ...... Slenojaora columnaris Schl ...... :Fenestella retiformis Schl ...... ~ Synoeladia virgulacea Phill ...... i :Phyllopora ehrenbergi Gein ...... i Thamniseus dubius Schl ...... Aeanthoeladia aneeps Schl ...... E

Echinodermata.

Cyathoerinus ramosus Sehl ...... ! I Areha~ocidaris verneuiliana King v,r, v.r~

Brachiopoda.

! Discina speluncaria Schl ...... Productus horridus Sow ...... ~ ! 1)roductus umbonillatus King ...... Strophalosia lamellosa Gein ...... ! Strophalosia goldfussi Mfinst .... V.C, v.r~ ' Streptorh,yr~chuspelargonatusSchl. i Camarophoria schlotheimi v. Buch CamaroThoria globulina Phill ...... Camarophoria multiplicata King.. ... Trigonotreta alata Schl. and

variants ...... ~ Triqonotreta cristata Schl ...... v.r. ... Triqonotreta multiplicata Sow. ,,~

Clelothyris peetinifera Sow ...... Martinia elannyana King ...... ,.. ~ :Epith.yris elongata Schl ...... :ETithyris su~ata Schl. V.Co V.C~ V.Co

Q.J.G.S. No. 274. Q Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

216 MR~ C. T. TRECHMANN 051 k MASS OF ANHYDRITE [Juno x9x 3,

FossiLs O~ THE MIDDLE MAI}NESIAN LIMESTONES IN THE HARTLEPOOL AREA (continued).

Highest Bedded LowerShell- Bryozoonal Shell- Shell-Limestone Shell- Middle Lime- Limestones of ! Conglomerates. Lime- Lime- Castle-Eden Dene. AMES stone. stones, stones.

OF ~

SPECIES. ,._, t~-j ,~

,.-., ~ N

Lamellibranchiata.

Pecten pusillus Sehl ...... ". ' , .. King ." ii ""i , Lima permian~z * v.r...... Schl ...... , Monotis spelvnearia C C ...... Sow.. , Mytilns (Liebea) squamosus ... C ......

lgdmondia murchisoniana King ... , ...... Bakevellia ceratoTh_a[la Sehl ...... , * C r C Bakevellia antiqua M'iinst ...... , * r V.C, * B!/ssoarca striata Sehl ...... , * r

Byssoarea cf. kin#iana de Vern ...... * ......

Cardiomorpha modiolifor~nis King , ... c Pleurophorus eostatus Brown ...... : ,

8vhizodus truncatus King ...... ' , ... ,

Astarte vaHisneriana King ...... i ......

Astarte cf. tunstallensis King ...... ~ ...... Allorisma ele#ans King ...... ,

Oasteropcda. ]

Chiton cf. loft.us*anus King ...... : ......

Turbo helicinus Sehl ...... , * v.c. C ...

Turbo thomson*anus King ...... i ...... * ...

Turbo taylor*anus King ...... i * ... .. Loxonema sp ...... , ......

Macrocheilus sp ...... ~ ......

~uomphalus Term*anus King ...... , ...... Nat*ca leibnitziana King ...... , ......

.Nat*ca of. minima Brown ...... V.C .... l~leurotomaria antrlna Schl ...... , v.r.

laleurbtomaria tunstaHensis King. ? * ... V.C .... Pleurotomaria nodulosa King ...... , ~leurotomaria linkiana King ...... , ......

Minute indeterminate gasteropoda .... 9 r

Cephalopoda. Nautilusfreieslebeni Gein ...... * V.C. * -Nautilus bowerbankianus King ... ,

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Vol. 69. ] I1~ TItE MAGNESI.~.I~ LIMF_~TONE AT HAETLBP00I.. 217

(1) The Magnesian Limestone, in the district here described, in its original condition of deposition contained very large quantities of calcium sulphate, as shown by several borings entering or piercing the Magnesian'Limestone where it underlies the Red Beds or other protective covering. (2) This calcium sulphate has been completely removed by the action of percolating waters, wherever the Magnesian Limestone has been divested of its protective covering of comparatively impervious Permian and Triassic red marls and the associated beds. (3) A mass of anhydrite, apparently by reason of its exceptionally large size, has escaped complete removal ; and, because its denuda- tion and erosion were more rapid than was the case with the surrounding Magnesian Limestone, it has given rise to the ' slack' or valley which now accommodates the harbours of Hartlepool and West Hartlepool. (4) This mass of anhydrite overlies a gypsiferous (protected) Magnesian Limestone containing fossils of the Middle Division (Shell-Limestone), and so must represent the time-equivalent of ~Lpparently part of the Middle, and of a great part of the Upper Limestones. (5) :Evidence goes to show that the sulphates in the Magnesian Limestone were originally deposited as anhydrite, and that this an- hydrite was converted into gypsum before removal. The bands of limestone which are interbedded with anhydrite towards the base of the anhydrite-mass represent Magnesian Limestone in its original condition. The gypsiferous limestones which occur beneath the anhydrite-mass at Hartlepool or other areas represent an inter- mediate stage between the unaltered rock and the completely gTpsum-free limestones at the surface. (6) The removal of soluble sulphates from the formation has brought about a degradation and settling-down, with a consequent decrease in volume of the Magnesian Limestone, resulting in (a) A mechanical collapse of parts of the strata with consequent brecciation ; and (b) an intense porosity in those beds where the su]phates impregnated, or existed in close association with, the carbonates. (7) The porous condition in which parts of the formation are left after removal of the sulphates lays it more open to processes of segregation and differentiation of the two carbonates, with pro- duction of hard calcareous breccias associated with powdery material rich in magnesium carbonate, which are an obvious feature of the formation in its present condition. The subsequent removal by water (by solution or by mechanical means) of the powdery material brings about the dedolomitization of parts of the formation on a more or less extensive scale. (8) Analysis of obviously less-altered portions of "the formation goes to show that the Middle and Upper Magnesian Limestones were originally deposited in a highly dolomitic condition. While the variability in composition of the Lower Limestones, where a2 Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University Library on November 25, 2015

218 A~BYDRITE-~ASSI~r ~rS ~tAOI~SlA~r LIMr:s~0~r. [June I9t3, more purely marine conditions prevailed, is largely due to conditions of deposition, the Middle and Upper beds were deposited in a sea more completely isolated from the oceans, and undergoing con- centration, but never complete desiccation, until perhaps the deposition of the salt-measures. This view is entirely supported by evidence deducible from the nature of the fauna. (9) The distribution of the fauna in the Middle Limestones was largely influenced by the quantity of sulphates present in the sur- rounding waters in the Permian Sea. The highly fossiliferous Shell-Limestone indicates an area of comparatively sulphate-free deposition, where the fauna consequently flourished and influenced the sedimentation by its remains. The present distribution of the Shell-Limestones indicates the possibility that current-action in the Permian Sea was the determining cause of the comparative absence of sulphates. (10) The increasing deposition of sulphates prevailing towards the top of the Shell-Limestone brought about a gradual extinction of the fauna, with a progressive dwarfing of those forms which survived, until the Uppermost Shell-Limestones yield a fauna which, though still typically Middle, yet approaches in character that of the braehiopod-free Upper Limestones.

EXPLANATION OF PLATE XXII. Map of the t/artlepool area, showing the position of the anhydrite and the Magnesian Limestone, on the scale of three-quarters of an inch to the mile, or 1 : 84,480.

])Isc~sslo~. Dr. •. W. EvANs commented on the interest and importance of the occurrence of anhydrite and gypsum ill the Magnesian Lime- stone, either disseminated through it, or forming lenticles of various dimensions, in striking similarity to what was met with in the same formation in Germ'any. On the reading of Dr. Woola- cott's valuable pamphlet on the rocks of Tyneside before the Geologists' Association last May, and afterwards during the excur- sion to that district, the speaker had insisted that the true explana- tion of the brecciated structure of the Magnesian Limestone in the neighbourhood of Sunderland was the former presence of gypsum, representing original anhydrite, which was afterwards dissolved .out ; and that the cellular and porous condition, which likewise resulted from the solution of the gypsum, favoured the formation of the concretions for which the locality is famous. In times when the rock was saturated with moisture, the excess of car- bonate of lime over carbonate of magnesia would be dissolved, to be precipitated again in concretionary structures in times of desiccation; ~vhile the residue, containing lime and magnesia, approximately in the proportions of dolomite, would resist solution and remain as that fine powdery material which is found in the cavities when they are first broken open. This had been only a speculation, but the Author had shown that it was founded on fact. Downloaded from http://jgslegacy.lyellcollection.org/ at Carleton University ['ou![-HnuLibrary J uopp.tq on November~ saluo.tpu.t 25, Ioodol~aeH 2015 UlOa.I dutu oq7 ssoaoe spa~lsoa~-qmos ~tuuuna au!i ~iotqq ~[o.tq~ oq3. "o~.tapitlU~ atll $o pu~ 's!t D jo ~seo oql ol so![ ~oo(i ~!ao:lo!A "ss~tu ol!ap.(quu ot[~l jo ou.qlno olquqoad oqq s.~oqs oo~ds I'oao oq3~] "a~aa~O uol~oS "O "I°°d°l~a~H qsaAk 's~[a°~aa~"Ak "9 "[oodol~H 's~iaOAk-~uotuoo uoaa~A~t "g "I°°doll'i~tI ~soA~ 's~[-loA~.-~uouloD "8 "~.IO.tIO.t~ ~to!.~suna~I "q .qa~ H "g "s~IaoA~-dIncI "1 "~[a°q~°H "t" "Iao.t[loO II~tpl°~lff "I "slhqzoR ,IO ~s!'I

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