I. Introductory

Downloaded from http://jgslegacy.lyellcollection.org/ at University of Kentucky on June 27, 2016 trol. 58.] ~aF.CCIAS AND THE PHYSICAL GEOffrR&PHY OF TItEIR A.6~:E. 185 12. On the I~EL&TIOI~of C~R'rXlN BRECCIXS to the 1)~IYSlCAL GEO~RAP]t~ of ~HmR AOE. By Prof. THomAs GEo~as BosNia, D.Sc., LL.D., F.R.S., F.G.S. (Read February 5th, 1902.) I. INTRODUCTORY. :BREccI~s and conglomerates have always attracted me, and the former especially since I had opportunities, about ten years ago, of examining one of the most interesting examples in Europe. They afforded problems, to which I failed to find answers in all respects satisfactory ; so in the hope of obtaining further information I spent, during the summer of 1900, some days in the Western Thiiringer- wald, with my friend the Rev. Edwin Hill, in order to study the noted breccias of the Rothliegende, and last July again examined, and more fully than before, the beds of breccia, sections of which are well displayed along the high road in the Val des Ormonts above Le Sepey. In former years I had visited the Permian Breccias of the English Midlands and those now assigned to that period in Devon. All these exhibit certain features in common, some of which are also found in the so-cMled Dolomitic Conglo- merate in the South-west of England. So I purpose to give a brief summary of the principal characters of each of these deposits, .concluding with some comparatively modern breceias, in order that, if I cannot completely unravel their history, I may at least bring the more significant facts into a clearer focus) These I have never had an opportunity of examining, but gather the following facts from the careful descriptions which have appeared in print. 2 The beds of Brockram are intercalated in the red Penrith Sandstone, which in the vicinity of that town is un- interruptcd either by them or by shales. Brockrams can be traced in a north-westerly direction from Kirkby Stephen to beyond Appleby, '~ and are also strongly developed in Dumfries-shire, where they thin towards the south or south-west. The authors of the Survey -~[emoir 9 describe in the Appleby district two Brockrams, separated by a mass of false-bedded red sandstone, the lower one of which they describe more minutely. This (according to :~r. Woodward's 1 I have referred in the course of this communication to the books and papers which I have consulted with profit; and I have to thank Dr. W. T. :Blanford, Dr. R. II. Scott, Prof. Garwood, and Mr. Wickham King for their great kindness in giving me infbrmation in reply to enquiries. 2 Mere. Geol. Sarv. 1897 ' Appleby, Ullswater, etc.' p. 72; and papers by Murehison, tIarkness, Goodchild, Irving, and others, for references to which see H. B. Woodward's ' Geol. of England & Wales' 2nd ed. (1887) s.v. Permian p. 210. 3 From one town to the other is about 10 miles. Downloaded from http://jgslegacy.lyellcollection.org/ at University of Kentucky on June 27, 2016 186 rROF. BONNEY ON THE RELATION 0V BRECCIAS ~May 19o2 , summary 1) is sometimes 100 feet thick, and the upper 150 feet. :But a diagram drawn by Mr. Goodchild : shows that there may be more than two beds : the solid Brockram-mass at Kirkby Stepheu tailing off wedge-fashion as it approaches Appleby. The lower bed is strongly jointed, forming bold mural escarpments, and often supplying a good building-stone. The fragments are usually crowded confusedly together in regard to size, though their longer axes tend to lie parallel with the bedding-planes. Those about 2 inches in diameter dominate, but they run down to mere grains on the one side and occasionally up to blocks 2 or 3 feet in diameter on the other ; being either angular or but little rounded. As a rule from 85 to 90 per cent. are Carboniferous Limestone, the remainder being sandstone from the same system, 3 with a little chert, and shale. A few rounded pebbles of liver-coloured quartzite have probably been derived from some older conglomerate. A red sandstone occasionally forms subordinate bands in the Brockram, and the middle mass of that rock is strongly false-bedded. The fragments are hardly ever striated, but in one case the discoverers were satisfied that the marks were due to ice-action. The materials in the Dumfries breccia represent the rock of that district. ~ These Broekrams have evidently formed a marginal fringe to a rocky or mountainous region. :Mr. Goodchild, who considers the ordinary Penrith Sandstone to be a desert-formation, suggests that the Brockrams were transported by shore-ice and deposited in water. ~ If so, the drift must have been (roughly) north-westerly in the one district and south-westerly in the other, the sand being indicative of winds blowing more directly from the east. III. TItE Aa~AoH BR~CCIAS. Beds closely resembling these Broekrams, according to Prof. Hull, '~ occur in the Permian of Armagh. The sections described exhibit in the lower part a bed of breccia, 10 or 12 feet thick, composed (as I infer) of more or less angular fragments, embedded in a reddish sandy matrix, which passes locally into sandstone. The upper surface of this sometimes is eroded; at others the mass graduates into a stratified conglomerate and boulder-bed, the blocks being from 18 inches to 2 feet in diameter. These vary from angular to rounded, consisting of grit, felspathic sandstone, vein- quartz, and occasionally of limestone. Proi: Hull says that the boulders of grit (Silurian and Old Red Sandstone) must have travelled from 20 to 30 miles, and he attributes a glacial origin to ttle deposit. i 'Geology of England & Wales' 2nd ed. (1887) p. 212. The thicknesses given in Harkness's paper, Quart. ffourn. Geol. See. vol. xviii (1862) p. 206, are considerably less. 2 Geol. Mag. 1882, p. 223. a In one locality the bulk of the fragments consist of this sandstone. 4 The ' Crabroek' of the Barrow district probably is a kind of brockram, and a thin bed of breccia forms the base of the Permians near Whitehaven. Trans. Cumberl. & Westmorl. Assoc. re1. ix (1885) pp. 46-47. Quart. Journ. Geol. Soc. vol. xxix (1873) p. 402. Downloaded from http://jgslegacy.lyellcollection.org/ at University of Kentucky on June 27, 2016 Vol. 58.j ~'o THE PHYSICAL GEOGRAPHY OF THEIR AGE. 187 IV. NORTB[-EASTERN ENGLAND. A seam of breccia sometimes appears at the base of the Permian in North-eastern England. This, in the Nottinghamshire district, was described by the late Edward Wilson ~ as attaining a maximum thickness of about 4 feet and consisting of angular to subangular fragments--sandstone, ironstone, and shales from the neighbouring Coal-Measures, with similar fragments of slate, quartzite, quartz, etc. ; these seams of breccia also occur locally in the overlying sandstone. This basement-breccia, he states, maintains its average thickness and coarse texture, and mus~ have been simultaneously deposited over a considerable number of square miles. It might be attributed, in his opinion, to droppings from melting icebergs or 9 . | 9 floes, but he remarks that, as it comes above a line of eromon, no special explanation may be needed. He regards it as the base of the equivalent of the ' Marl-Slate,' the Rothliegende not being represented in this district. V. THE MIDLAND ~RECCIAS. Some of the most important sections of this breccia are well exposed on the Clout Hills, along the margin of the Malvern- Abberley range and to the west of Enville, cropping out over an area of about 500 square miles; but they have also been found, though thin, in Leicestershire. In the former region they attracted the attention of geologists more than sixty years ago; but full descriptions have been given and their origin discussed, by the late Sir Andrew Ramsay, ~ Prof. Hull, ~ and recently by Mr. Wiekham King. ~ In the Enville district the breccia is underlain by a mass of sandstones, interstratified with marls, about 850 feet thick (maximum), in which are two beds of conglomerate, rather local, one of which attains to 60 or 80 feet. Here the breccia is followed by sandstones and marls, its principal outcrop running in a general north-westerly and south-easterly direction, and the greatest thickness being about 225 feet. In the Clent district the breccia attains its maximum, 450 feet, and covers Wychbury Hill (about 750 feet), Clent Hill (997 feet),' Walton Hill (1036 feet), and Romsley Hill (930 feet). ~ Here it runs nearly north to south, parallel to, and mainly on the western flank of, a strip of older Palmozoics, from the northern end of which it continues in a north-westerly direction. The breccia is rudely stratified, and is occasionally interrupted by thin layers of sandstone, its materials becoming rather less worn in the upper parts until it passes into marl ; the fragments vary from angular to subangular, and are very commonly from 5 to 6 inches in diameter, 1 Quart. $ourn. Geol. Soc. vol. xxxii (1876) p. 535. 2 Ibid. vol. xi (1855) p. 185. 9~Mem. Geol. Surv. 1869' Triassic & Permian Rocks of the Midland Counties.' 4 Quart. ffourn. Geol. See. vol. iv (1899) p. 97 ; see also Prec. Geol. Assoe. vol. xv (1898) p. 372. i W. Wickham King, ' Midland Naturalist' vol. xvi (1893) p. 25. Downloaded from http://jgslegacy.lyellcollection.org/ at University of Kentucky on June 27, 2016 1~8 PROF. BONNEY ON THe, REL,kTION OF BItECCIAS ~May x9o2 , but those of smaller size are numerous.

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