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. 



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