The Geology of the Appleby District, Westmoreland
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129 THE GEOLOGY OF THE APPLEBY DISTRICT, WESTMORELAND. WITH SPECIAL REFERENCE TO THE AREA TO BE VISITED DURING THE LONG EXCURSION OF 1907 Dv JOHN EDWARD MARR, Sc D, F.R S (Read July Silt. I907) CONTENTS PAGE I -Introduction I~9 II -The Lower PalreozOIc Rocks · 131 ] II.-The Old Red Sandstone Penou · 134 TV.-The Carbomferous Penod • • 135 V.-The New Red Sandstone Rocks 136 VI -Intrusive Igneous Rocks 138 VII -Glacial Phenomena 140 YIII -PhysIOgraphy 141 References 147 I -INTRODUCTION HE geologIcal structure of the Appleby Dlstnct IS of par• T tIcular Interest, for It determmes one of the dommant physical features of our Island-namely the Pennme Chain or Backbone of England. The country ImmedIately around Appleby forms compara• tIvely low ground, between the heIghts of the Lake Dlstnct to the west and the Pennme scarp to the east Through thIS low ground runs the nver Eden, and thIS low country has been termed Edenslde by the late Mr GoodchIld. The general pOSltlOn of Edenslde is shown on the accom• panymg map (Plate II) by the stIppled portlOn of New Red Sand• stone extendmg In a N.N. W. dlrectlOn from KIrkby Stephen, past Appleby, to wIthIn a few nl1le~ of the CIty of CarlIsle, where It passes Into the north-Cumbnan plam lymg east of the Solway. The map, Plate II (by the late J. G. GoodchIld), also shows the dIstnbutIon of the pnncIpal geologIcal formatlOns. EdensIde IS geologIcally a synclme between the Lake DI5trict antIclIne to the west and the Penmne antIclIne to the I'ROC. GEOL. Assoc., VOL. XX, PART 3, 1907.J II 13° JOHN EDWARD MARR ON east, but the eastern 11mb of the synclllle IS cut offby the prinCipal Penmne fault, and accordmgly we find, apart from detail, a repetitIOn of the rock-groups which occur to the west of the fault on Ib eastern side, and the general dip IS m an easterly directIOn, save in the case of the highly convoluted Lower PalceozOlc rocks ~.=! Standlllg on a promInent ~ ~ height near Appleby, we 5ee to ~~ the west the Lake DI5tnct " ~ c" c" hlll~ of Lower Palceozolc rocks, "'" " nearer are the hills between "i 0...0..." " "... Shap and l'ennth, formed by the M~ V overlymg Carbomferous strata, "::! " I ~ " and the ground on which we Jzl c- B ~'" ~ 5tand con~lst:; of the yet more Ul § ~~'" Z recent New Red Sand5tone '"<=: ;:: Turl1lng to the ea~t the POSI• ~ tIon of the Important Pennme Ul "'"Ul 0 0 .c" Fault IS shown by the 5udden ~ u " rise of the great Pennll1e ~carp ~ "S With the Lower PalceozOlc hills z t: ~ 0 (fJ of comcal shape III the fOle• [:: " "- U 0 if ground The fault runs between ~ the latter and the New Red If.'" -" OJ bn [f, Sandstone ...:'-' ~ ..-l" " If we cro~sed over the Pen• t) " Z ~ mne Cham we should reach the '" i3 N "E '" 0 '" New Red Sandstone of the tract "I 8 "ou: around the mouth of the TLe~, 0...~~~ _ v '"~ thus traverslllg between the fault .... § ~ '-' ~..c a: and Tees-mouth the same rocks <5 ~ 11) ~ ..... uZ over which we pass when "alk• Illg from the eastern confines of .... N '" the Lake District, past Shap and Appleby, to the Pennme Fault The SectIOn (Fig r 3), III which details are omItted, ~ 5hows the general he of the '"ii rocks to the summIt of the '"''" PennmE' Cham i:! 00" The stratified rocks WIll be :n "" described III the order of their i:! antiqUity, begmnlllg with the most anCient. THE GEOLOG \" OI THE APPLEBY m;:,TRICT, \\ E"nIORELAND I 3 I THE GEOLO(,IC\L DEPOSITS FOUND IN THE ApPLEBY DISTRICT. r Recent (AlluvIUm peat, etc ). QUATERNAR\ \. Glacial (boulder clay, sand, and gravel) St Bees Sandstone. MESOZOIC J TrIas { Gypseous Sandstones and I Marls MagneSian Llme~tone and Plant Beds. PermIan J Upper Pennth Sandstone. Upper Brockram Lower Pennth Sandstone UPPER.r l Lower Brockram P AL:EOZOIC f Millstone Gnt Carboniferous Limestone Carbomferou~ SerIes. I Sand~tones, shales, and con· ~ glomerate~ Old Red Sandstone (PolygenetIc conglomerate). ~ Brathay Flags. SilurIan 1 Stockdale Shales. AshgIll Shales r Staurocephalus and Kelsley LOWER 0 d D~~:~s~~:l~s. P ALtEOZOIC 1r OHClan f Corona beds lBorrowdale V oleanlc rocks Sklddaw Slate~ with Milburn V oleanlc rocks II.-THE LOWER PALiEOZOIC ROCKS. The Lower PalreozOlc Rocks occur In an inlIer to the east of Edenslde (see the Map, Plate II, and SectIOn, FIg. 13), extendIng III a directIOn nearly north and south from the neighbourhood of Melmerby to the western flanks of Roman Fell, havll1g an average Width of about a mIle. On the west they are separated from the New Red Sandstone, as already stated, by a great fault, III many respects the most Important III the dlstnct This has generally been spoken of as the Pennllle Fault, but the Geological Surveyor" term It the Outer Penmne Fault, glVll1g the terms Inner Pennll1e Fault and Middle Pennllle Fault to two other faults whIch we Will now notIce The Il1ner fault on the" hole separates the Lower PalreozOlc rocb from the Carbol1lferous roch of the great escarpment, though a few patches of Lower PalreozOlc rocks occur to the east of It III one or two valley bottoms, and the Carbomferous rocks on the top of Roman Fell are on Its western I3 2 JOHN EDWARD MARR ON sIde. Its throw IS not very great. The MIddle Fault along the greater part of ItS course dIvIdes two group" of Lower Pal<eozolc strata, the older lymg to the east, and the newer to the west of the fault-lIne SectIOn (FIg 14) shows the effects of the three faults. (I) The Sklddaw Slates -Along the stnp of country between Melmerby and Roman Fell, bounded by the mIddle and Inner PennIne faults, occur rocks whIch are correlated with the Sklddaw Slates of the Lake DIstnct They consIst chIefly of glossy black or greYIsh badly-cleaved slates WIth thIn grIt bands. In a few places, as at EllergIll, are more earthy shale5 WIth GraptolItes These, whIch are apparently newer than the main-mass of slates, are of Aremg age. The mam-mass may be partly Arenig and partly of older date, but In the general absence of fossIls lIttle need be saId concernmg It, for we shall pay httle attentIOn to ItS rocks dUrIng the excUi slOn. w E. FI F2 F3 ~; 4 FIG I+ -SECTION ACROSS THE PENNINE FAULT - Y E Mal r. Length of SectIOn about 2 mIles. I. Sklddaw Slates Fr Outer Fault 2. Upper OrdOVICIan and SIlUrian. Fz MIddle Fault 3 Carbomferous. F3 Inner Fault 4 New Red Sandstone Above the EllergIIl Beds are graptolIte-bearmg shales WIth Intercalated ashes and lavas, markmg the change from the non-volcamc Skiddaw Slates to the volcamc Borrowdale Rock,;. These were called the MIlburn beds by the late Mr. GoodchIld. Certam volcamc rocks at the north-west corner of Roman Fell may be of the same age as the MIlburn beds (2) The Borrowdale Volcantc Rocks (LlandeIlo )-Near the northern extremIty of the InlIer, and still between the mIddle and mner faults, IS a group of contemporaneous porphyntlc and veSIcular baSIC andeSItes and ashes whIch are undoubtedly the eqUIvalents of the well-known Eycott HIll rocks, north-east of KeswIck, the latter occur some way down m the Borrowdale Senes The hIghest rocks of the BorrO\,dale Senes are found In the block between the mIddle and outer faults, and pass up mto the hIgher OrdovIcIan sedIments They comlst of rhyolites and rhyolItIc ashes, and form several of the conical hIlls of the mlIer, THE GEOLOGY OF THE APPLEBY DISTRICT, WESTMORELAND. 133 mcludmg Knock PIke and Dufton PIke. On these PIkes they are usually very rotten, and the best exposUles are found m the stream-courses, espeCIally m Swmdale Beck, where one of the lavas IS of great Interest. It IS descnbed by Mr. Harker as an "eutaxIttc" rock wIth discontmuous band~ of crystallIne character consisting of clear felspar quartz and decompositIOn product5. It has caught up fragment5 of an earlIer Andesitlc lava, and the flow-lines stream around these fragment5 The highest bed of thIS senes m Swmdale Beck IS an ash whIch IS Immediately succeeded by fos51lIferous depOSits, themselves contalnmg ashy matenal. The rhyolItiC group of the mlIer IS qUite comparable with that which forms the 5ummlt of the Borrowdale Senes m the Lake District The general stnke of these and the succeedmg rocks IS W N.W and ESE, but they are repeated several ttmes owmg to faults which cross from the outer to the middle Penmne faults With a general N.E. and S W. trend. These cross-faults produce five mam blocks of strata, one at the extreme northerly end of the inlier north-east of Melmerhy, the second With Knock Pike and Swmdale Beck, the thud wIth Dufton Pike, Pusgtll, etc, the fourth With Gregory and Kelsley, and the fifth WIth Roman Fell and part of Hilton Beck Each of these blocks dIsplays the rhyolIttc senes. (3) The CorOlla Beds -These conSIst of ashy calcareous shales, and argIllaceous limestones, the latter sometimes largely composed of Beyriclua. The beds are seen m theIr proper posItIOn m Swmdale between the rhyolIttc senes and the over• lymg Dufton Shales, but the most fOSSIliferous localIties are the Alston Moor Road near Melmerby, PU5glll, and the flanks of Roman Fell. In addItIOn to the type fOSSil Trematzs corona, Llllguia temtigralIItiata seems to be confined to thiS group The bed5 are probably of Lower Caradoc age. (4) The Dufton Shales.-Dark grey or black cleaved shales With much calcareous matter, and thm bands of limestone, greatly folded, so that no accurate estimate of thickness can be made, but they are probably not more than 500 ft.