GEOLOGY them may be derived from rocks that occur within 10 or 20 miles. The occurrence of these beds seems to indicate the margin of a large mass of land occupying this part of England, the cliffs of which furnished the debris that was transported a short distance, and mingled with the marls and sands of the neighbouring sea. The origin of these rocks has given rise to much con- troversy. Ramsay considered that they were the morainic matter of old glaciers existing in Permian times. 1 Jukes thought they were the debris derived from neighbouring rocks now concealed beneath the Trias, 2 and this view is the one now generally held by geologists at the present time. The outcrop of these rocks is most irregular, but they appear to occur principally along hollows in the underlying Carboniferous rocks. The unconformity between them is very marked along the western side of the coalfield, the breccia occurring in patches of no great thickness, and being frequently overlapped by the various members of the Trias. The thickest beds of breccia are those at the southern end of the coalfield about Measham, Packington and Donisthorpe. TRIAS The Trias covers the largest area of any formation in this part of the Midlands, and extends from west to east over a distance of from 50 to 80 miles. It consists of the following subdivisions : Rhaetic K _ f Red marl with thin bands of sandstone. I Red, white, and brown sandstone with thin beds of marl. Bunter Pebble-beds and beds of sandstone. Of these rocks the Keuper covers the greater part of the district ; the Bunter, which is thinning out rapidly in this area, occurs only at a few isolated places around the western part of the Coalfield ; while the Rhaetic Beds crop out as a narrow band running from north to south nearly across the centre of the county. BUNTER The Bunter consists mostly of beds of shingle with occasionally some beds of soft sandstone. These pebble-beds are formed of partially con- solidated quartzose gravels which pass into alternations of more or less pebbly sandstone. The pebbles themselves are mostly brown and grey quartzites, and the matrix of the rock is in many cases so hard and con- solidated that they fracture more readily across the pebbles than between them. They are often covered with small indentations or pits caused by pressure or chemical action where they are in contact. 3 Professor Sollas considers that they are caused by earth tremors.* The origin of these pebbles and the manner in which they have been formed are questions concerning which there is a great diversity of opinion. 6 These beds probably have a 1 Quart. Journ. Geol. Soc. xi, 198. 1 Memoirs of the Geol. Surv. : 'South Staff. Coalfield,' 2nd ed. 3 W. S. Gresley, Geol. Mag. dec. iv, vol. ii, 239 ; T. Mellard Reid, ibid. 341. 4 Brit. Assoc. Rep. for 1893, p. 755. ' C. Lapworth, Proc. Geol. Assoc. xv, 382 ; T. G. Bonney, Quart. Journ. Geol. Soc. Ivi, 279 ; and O. A. Shrubsole, Quart. Journ. Geol. Soc. lix, 311. 9 2
