8. ]~Ie G~OT, OGICAL STRVCTW~ of the S Ow
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Downloaded from http://jgslegacy.lyellcollection.org/ at Orta Dogu Teknik Universitesi on January 17, 2016 Vol. 55.-J . aE0r.0GICAT. STRUCTURE OF TWE SOUTHERN MALVERNSo 129 8. ]~ie G~OT,OGICAL STRVCTW~ of the Sow~,a~ ~[ALv~a~S, and of the AmAcE~r DIsTmc~ to the W~,sz. By Prof. T. T. GROOM, :M.A., D.Sc., F.G.S. (Read December 7th, 1898.) [PLATES XIII-XV.] CONTENTS. Page T. Historical Summary ............................................................ 129 II. General Structure of the Area ............................................. 130 III. The ]Kalvern Range ............................................................ ] 31 (1) Raggedst~)ne Hill. (2) 1Kidsummer and I-[ollybush Hills. (3) The Central Depressions in the Hills of the Southern Part of the Range. (4) The Hol]ybush Pass. (5) The Gullet Pass. (6) Chase End Hill (7) Confirmatory Evidence from the more Northerly Portions of the Range. (8) Theoretical Explanation of the Structure of the Southern Portion of the Malvern Range. IV. The Western Tract ............................................................ 157" (1) The District of White-leaved Oak, etc. (2) The District around Fowler Farm. (3) The District around BronsiL V. The May Hill Sandstone Escarpment .................................... 166 I~ ~'tISTORICAI, SUM]WARY. EASILY accessible, situated in a charmingly picturesque country, an~ marking some of the most interesting phases in the evolubion of the British Is]es, the Malvern Hills have now for nearly 80 years formed the subject of geological investigations, and have ever yielded new facts of interest and importance. Leonard Horner I described the Malverns as a granitic mass in- truded into the associated strata. Murehison 2 regarded the chain as essentially of igneous origin, though including ' Silurian' beds altered by the intrusion. Phillips, in his masterly work on the district, 3 maintained that the Lower Palmozoie strata associated with the range had been deposited against the crystalline rocks. I4o11, 4 regarding the range as probably composed of pre-Cambrian metamorphosed sedimentary and igneous rocks, described the Cam- brian aud Silurian beds as overlapping the metamorphic series. :Mr. Rutley 5 considers that the gneissic and schistose rocks of the Malverns are a series of altered tufts, grits, sandstmnes, and volcanic '- Trans. Geol. See. set. 1, vol. i (1811) p. 281. 2 , The Silurian System,' 1839, pp. 417 etseqq. ; ' Siluria,' 1854, pp. 92et se~lq. 3 Mag. & Journ. of Sci. vol. xxi (1842) ; Mere. Geol. Surv. vol. ii (1848) pt. i, pp~ 66 et seq~. & pp. 125-126. Quart. Journ. Geol. Soc. vol. xxi (1865) pp. 89, 92, 97 et seqcb 5 l&id. vol. xliii (1887) p. 508. Q. J. G. S. iNo. 218. x .~176 N ,, r #." ::2":1! 7:::..':V)"::!::..:i::;i.i.:. i o 0 c~ iJ .:iiii,ili7 0 Downloaded from http://jgslegacy.lyellcollection.org/ at Orta Dogu Teknik Universitesi on January 17, 2016 "-".:::" ~-~ 22 :.:: "-'14"o~".: "'. "~;'-:'.-.':"..'. :.':':. i:. ~? ::::.': ". -:-~ :;.';'-:.-i:":(-~:.l//~ ::...: : ~ ,. .... , ,-- Faults '.::...:-).!:.:':!i:;"':'":"'"::::"~:~::"~=~":~~ V ~" .... tObscu,'e Faults ~ ~'~.-'~'X''~'''- ~'~" ," "~'~'" '~='z:~ '=' "'"' .... (and Boundaries. 300............. 326 z~ ~.-;~" ,~.,~'~'"~2 " ,~',Z~,","~r .-,~ ~.. ~ / .,"" GEOLOGICALlAP ~~/~ :" SOUTHEBN PART Scalc: 4 i,~chcs lo lhc relic. ""'N"~'~ MALVERNS. • Drift ~Trias [-~HaffieldBreoeia ~MayHill8aJ~dstonel I" ~J ( 'P~rmam ) I : : " : :'l and Conglomerate IBasalt &DiabaseV////Crey Shales ...... ~ Hollybush i .o//rb.sh Co,,oMo,,,. ~ Malvernia n "wuuu~ St,ilce of tJlaCK SRales ~ Sandstone erate and Quartzite { A ,chaean ) ~r~Juuuw~ Schiszs and Gno."ss ~ Breccia [No~e.~One or the bands of basalt, occurring in the :Black Shales on the western side of" ~[dsmnmer ]=fill has been unintenti0nMly omitted here, but it is shown in fig. 1. Further, the small fault immediately to the left of tt in 'HOLLYBUStt,' and soufll of' the dip-arrow marked 55 ~ is incorrectly reproduced. Its southern termination should be about r inch more to the west : this wou]d show the northerly direction seen in the actual exposure.] Downloaded from http://jgslegacy.lyellcollection.org/ at Orta Dogu Teknik Universitesi on January 17, 2016 f~ rm~ 0 O O 0 c~ C~ Downloaded from http://jgslegacy.lyellcollection.org/ at Orta Dogu Teknik Universitesi on January 17, 2016 o 0 I~, 84 0 . i-,,-.i 0 o r...D r~ 0 0 ~ 0 o A r/2 Downloaded from http://jgslegacy.lyellcollection.org/ at Orta Dogu Teknik Universitesi on January 17, 2016 130 PROF. T. T. OR00~ 0~ x~rR OZOLOOICAL [May 1899, and other igneous rocks. Dr. Callaway,1 on the other hand, regards the tbrmer series as metamorphosed plutonic rocks, chiefly granite and diorite, and compares them with the Archamn Series of Primrose Hill in Shropshire. The same author ~ recognized the volcanic series of the Herefordshire Beacon, and correlated it with the Urieonian rocks of Lilleshall Hill in Shropshire. The Herefordshire Beacon rocks have subsequently been studied by Green, ~ and by Messrs. Rutley, ~ Harker, 5 and Acland. 8 During the past year the present writer 7 has maintained that the Malvern and Abberley Hills are the basal wrecks of an old mountain-range which arose during Coal Measure times. II. GE_~IERALSTRUCTURE 01~ THe. AREA.s The area which constitutes the subject of the present communi- cation includes the southern end of the Malvern Range, as formed by Midsummer, Hollybush, Raggedstone, and Chase End Hills, together with the district~ of Coal Hill, Pendock's Grove, White- leaved Oak, Fowler Farm, and Bronsili, which lie immediately west of the range. This area is one of the most interesting in the Malvern district, because here the upheaval of the Palmozoie strata has been greater than elsewhere, and thus the Cambrian beds have been brought within the sphere of denudation 9whereas, along the rest of the range, the Silurian are the lowest Palmozoic rocks that come to the surface. The main axis of the joint mass of Midsummer and Hollybush Hills, like that of Swinyard Hill (from which it is separated by the Gullet Pass), runs about north and south ; that of Raggedstone Hill, which is bounded on the north by the Hollybush Pass, and on the south by the lower par~ of the ' Valley of White-leaved Oak,' runs :about north-west and south-east ; while Chase End Hill runs from north-east to south-west. On the east, these hills are bounded abruptly by the Trias, along an undulating line of fault. On the west, the lower parts of the slopes are formed almost exclusively by a flanking series of highly-inclined and much-dislocated Cambrian strata. At a short distance to the west of this southern part of the range is a half-lyre-shaped escarpment, well-marked for the greater part of its course, and formed by the May Hill conglomerates and sandstones. Between this escarpment and the Malvern Range is a partially- enclosed basin, or tract of generally lower ground, largely occupied 1 Quart~.ffourn. Geol. See. vol. xxxvi (1880), vol. xliii (1887), vol. xlv (1889), & vol. xlix (1893). 2 ]bid. vol. xxxvi (1880) pp. 536 et ,e~q. 3 Ibid. vol. li (1895) pp. 1-8. 4 /b/d. vol. xliv (1888) pp. 740 et seqq. 5 , Petrology for Students,' 1895, pp. 55, 143, etc. Quart. ffourn; Geol. Soe. vol. liv (1898)pp. 556~562. 7 :Rep. Brit. Assoc. 1898 (Bristol), p. 873. s Throughout this paper the signs M 100, 1~ 103, etc. refer to locMities corresponding to numbers in the map (P1. XIII), and to specimens collected at those localities. Downloaded from http://jgslegacy.lyellcollection.org/ at Orta Dogu Teknik Universitesi on January 17, 2016 Vol. 55-] STR~CTVl~,O~ ~av, sowmuU~ ~tALVEI~S. 131 by the Cambrian shales. For descriptive purposes this may be spoken of as the ' Western Tract.' Its surface is greatly diversified, owing to the presence of a number of intercalated bands and in- trusive bosses of andesitic basalt and diabase, as well as by the inclusion of several faulted blocks of ~ay Kill Sandstone. These masses form a series of continuous or interrupted ridges or eleva- tions, standing out more or less clearly from the surrounding lower ground. Some of the gentler elevations are capped or flanked by a stratified Drift of local origin. The district is, moreover, broken up by two small valleys, one running from the Kollybush Pass west- south-westward, and the other from the village of White-leaved Oak south-westward. The tract is partly under cultivation, and partly used as pasture- land; much of it towards the south, however, is occupied by woodland. The soil, in accordance with the varied petrographical ~haracter of the rocks, varies greatly in character, but is for the most part of rather poor quality. III. TH~ MALVEm~"RAI~GI~. (1) Raggedstone Hill. (Figs. 1-7.) It is proposed to examine first the structure of l~aggedstone Kill, ]~ecausc it is here that the mutual relations of the various rock- masses are best shown. The hill is approximately triangular in outline, and is divided throughout its length by a curved depression running from north to south right across its centre, two distinct summits being thus formed, each of which attains a height of over 800 feet (see P1. XIV). North of the summits the depression broadens out north-north- eastward, and forms a hollow known as Winter Combe. On the south, too, the depression widens, as it curves south-eastward. This depression marks a line of dislocation, as already shown for part of its course by Hell, 1 and by ~[r. Rutley/ The former points out that the character of the rocks and the strike of the schists differ in the two halves of the hill. In Mr. Rutley's map this fault is represented as terminated by a transverse fault on the south ; but I shall in the sequel give evidence to show that it probably runs the whole length of the depression. That portion of Raggedstone Kill which lies east of the depression is formed by a mass of Arehamn rocks : this, according to the two authors named, is divided by faults into three main blocks.