Downloaded from http://jgslegacy.lyellcollection.org/ at UCLA on June 21, 2016 138 PROF. r. T. ottooM o.s THE ozor.ooteAr. [Feb. x9oo , 8. On the GEOLOGICAL STR~rC'rUItE of POI~TmI~S qf the ~IALVERN a'~d ASBSRLmr HILTS. By Prof. T. T. GROOS, M.A., D.Se., F.G.S. (Read November Sth, ] 899.) [PLATEVII[--MAP.] CONTENTS. Page I. Introduction ......................................................... 138 II. Swinyard Hill ...................................................... i39 Itl. The Herefordshire Beacon ....................................... 140 IV. The Depression between the Herefordshire Beacon and Black Hill ......................................................... 145 V, Black Hill .......................................................... 146 VI. The Range between Black lIill and the Wyche ............ 147 VII. The Worcestershire Beacon and .North Hill .................. 149 VIII. The Abberley Range ............................................. 155 IX. The District of Cowleigh Park and Rough Hill ............ 155 X. The Patch (,f Archman and Cambrian near Martley ......... 163 XI. Woodb,lry, Wallsgro~e, Rodge, and Penny Hills ........ 165 XII. The Old Red Sandstone and Coal Measures west of Wal]sgrove Hill ............................................... 173 XIII. The Relation of the Coal Measures to Underlying Rocks in other parts of the Malvern and Abberley Di,tricts ... 176 XIV. The Uncontbrmity at the Base of the Upper Coal Measures in Districts other than those of Malvern and Abberley... 176 XV. The Directions of the ttercynian Movements in the Western Midlands ............................................. 179 XVI. The Relation of the :Folds of the Malvern-Abberley Area to those of Adjoining Districts .............................. 179 XVII. The Connexion between the Upthrusts or Ove-thrusts of the Archman Massif of the Malverns and the Overfolding of the Beds to the West ....................................... 182 XVIII. The Probable Evolution of the West-of-England Chain in several Sections not produ,'ed quite simultaneously ...... 182 XIX. The Relation of the Hattleld Breccia to the Underlying Formations ...................................................... 183 XX. The Relations of the Trias to the ' Permian' (ttaffield Breccia) and to the Older Rocks of the Malvern and Abberley Hills .................................................. 185 XXI. The Po~t-Liassic Faults .......................................... 189 XXII. Movements other than the Hereynian in the Malvern and Abberley Districts ........................................... 193 XXIII. Summary of the Structure of lhe Malveln and Abberley Ranges ............................................................ i93 I. Introduction. I7 ~ former communication 1 an account was given of the structure of the southern portion of the Malvern Rauge ; it is now proposed to supplement this account by a description of the rest of the Malverh Range and of certain portions of the Abberley Range, which were selected with the view of throwing light upon the geological tfistory of the Western Midlands. The structure will be traced i Quart. Journ. Geol. So.,. vol. lv (1899) pp. 129-168 & pls. xiii-xv. Downloaded from http://jgslegacy.lyellcollection.org/ at UCLA on June 21, 2016 Vol. 56.~ STRUCTURE OF THE UALVERN A~D ABBERLEY HZILLS. 139 from south to north, beginning with Swiny~rd Hill, which is situated immediately to the north of the area described in the writer's former paper. II. Swinyard Hill. The mlrrow ridge of Swinyard Hill is separated from Midsummer Hill on the south by the Gullet Pass, and from the ]:[erefordshire Beacon by the depression termed by Phillips ~ the ' Silurian Pass.' It has been pointed out on a former occasion 2 that the Gullet Pass is traversed by a line of fault. North of this line the width of the Arch~ean massif suddenly narrows, so that the deposits which flank the hill abut on the south directly against the Arch~ean mass of Midsummer Hill. The Archzean rocks of Swinyard Hill are well foliated towards the south, and show a marked plaoiocliual disposition. The ridge is flanked on each side by May Hill Sand- stone, forming ground with a slope decidedly less steep than that of the ridge itself, especially on the eastern side. The change of slope is usually somewhat sudden, and probably marks lines of faulting on each side; but the May Hill Beds are very badly exposed, and their actual junction with the Archman is not seen. The faulted character ,Jf the junctions seems to follow from their usually straight or zigzag course. The two rocks occur one on each side of the narrow path leading through the ' Silurian Pass.' This is the only spot where the May Hill Beds are actually seen ire situ. They consist, here of sandstones and thin impure limestone-bands, such as mark the summit of the May Hill Series. The southern side of the path is apparently formed by the faulted surface of the Archwan; this face dips E. 33 ~ N. at 60 ~. The sandstones dip north-eastward: that is, directly towards the Archa~an of Hangman's Hill, the southerly elevation of the Herefordshire Beacon. These relations suggest that the May Hill Beds are the remnant of a fold which has been overturned from the north-east, and overthrust by the Archman of the Here,%rdshire Beacon (see fig. l, p. 141). The May Hill Beds probably occupy most of the eastern slope of Swinyard Hill, down as far as the faulted boundary of the Trias. Symonds states that ' Wenlock beds ... have been seen still clinging to the eastern slopes of the Swinyard,' and that ' Wenloek corals have been tbund beneath the ddbris, in the garden of the cottage on the slope of the hill above the road to the Gullet quarry.' 3 No traces of these beds have been detected by the present writer. On the other hand, a portion of the upper part of Castle- morton Common is occupied by a southerly extension of the 'Warren House Rocks' (see Map, P1. VIII), which has hitherto escaped notice. The Silurian rocks west of Swinyard Hill are nowhere exposed close to the ridge, but abundant traces of the grey upper beds of the May :Hill Sandstone may be seen in I)laees. According 1 Mere. Geol. Surv. vol. ii (1848) pt. i, p. 29. 2 Quart. Journ. Geol. See. vol. lv (1899) p. 148. 3 , Old Stones' 2ud ed. (188Jr) p. 54. Downloaded from http://jgslegacy.lyellcollection.org/ at UCLA on June 21, 2016 140 PROF. T. T. GROOM O-'~ THE 6EOLO6]CAL [Feb. z9oo, to Symoncls, ~ the Cambrian conglomerate was formerly to be seen on the western side of the great quarry, at the southern end of Swinyard Hill. Untbrtunately, the relations of this formation t.o the Archa~an rocks of the quarry were not described. The Wool- hope Limestone, though badly exposed, may be traced by ddbris and by the steep slope that it forms, also by occasional exposures aleng a double line of outcrop0n the western slope of Swinyard Hill. The dip of; both bands = is easterly, and the area to the west and east of the western and eastern bands respectively is occupied by May Hill Sandstone; the limestone, theretbre, appears to form an overturned syneline. The supposed relations of the rocks at the northern end or" Swinyard Hill are shown in fig. 1, p. 141. III. The IIcrcfordshire Beacon. The Hertfordshire Beacon is certainly one of the most imposing and geologically interesting hills in the whole Malvern Range. It is bounded on the south by the ' Silurian Pass,' and on the north by a deep depression running from Wind's Point to Little Malvern. The w,estern and higher part of the hill is composed of rocks of the Maiverzfian Series; t,he eastern part is termed by the -' Warren House Rocks' of Hangman's Hill, Broad ])own, and Tinker's ttilL These reeks, first regarded by Hell 3 as metamor- phosed Cambrian, were compared by Dr. Callaway ~ with the rhyolitic Uriconian Series of Shr~pshirc; they have been studied by Green, ~ and by Mr. Rutleve and 3Jr. Aclan~l.7 They are shown to consist of rhyolites, andes|re.% basalts, and tufts; the bedding sometimes well marked, has a prevailing easterly dip. The line of junction between-the Uriconian and Malvernian Series runs along a marked depression, extending in a north-north- easterly direction from Clutter's Cave, and turning sharply east- north-eastward north of Tinker's Hill. South of Clutter's Cave the junction ia marked by no Surface-feature ; evidently it terminates against the patch of ~ay Hill Sandstone that occupies the' Silurian Pass.' South of Hangman's Hill the Uriconian Series comes directly into contact with the sandstone. The junction u-ith the Malvernian Series is nowhere actually exposed,-but the circumstance that it curves round eastward as it descends to lower levels suggests tha~ the plane off junction dips in that direction. In the absence of detailed knowledge of the disposition of the lava-beds and tufts, it is at present impossible to determine whether this junction is ~ fal, lt or a surface upon which the Uriconian series was originally deposited. 1 , Old Stones' 2nd ed. (188~).p. 24. 2 The eastern band is not. exposed at any point immediately west 'of Swinyard Hill, but it is seen dipping eastward near Walm's Well, immediately to the north. Quart. gourn. Geol. See. vol.xxi (1865) pp. 93, 94. 4 Ibid. vol. xxxvi (1880) pp. 536 et seqq. ~ Ibid. vol. li (1895) pp. 1 et Se~lq. Ibid. vu1. xliii (1887) pp. 481 et seqq. 7 Ibid. vol. liv (1898) pp. 556 et ~.eqg. Downloaded from http://jgslegacy.lyellcollection.org/ at UCLA on June 21, 2016 Vol. 56.] S'I'RI~C:tUREOF THE I~IALVERI~AND A-BBERLI~Y HILL8. 141 The rocks of the Malvernian series formthe most conspicuous part of the ]-[eretbrdshire Beacon. Towards the west this mass bulges out in a way suggestive of igneous intrusion into the Silurian Series. The rocks are, as a whole, massive rather than Fig. 1.--Section across the no,'thern extremity of I[anyman's Hill and Swinyard Hill.