TRIAS. 225 



the western counties is the Trias more clearly presented than in 

 the neighbourhood of Shiffnal in Shropshire. Along the cuttings 

 of the Wolverhampton railway all the subdivisions of the Trias, 

 together with the Permian and Carboniferous rocks, are opened 

 out in their order of succession.^ 



The Pebble-beds of Cannock Chase in Staffordshire consist 

 chiefly of quartzites, grey and reddish, and occasionally liver- 

 coloured, with also pebbles of white quartz and hard grit, felstone, 

 etc. Prof. Bonney has observed that one variety of the quartzites 

 is identical with rock that occurs in Ross-shire ; a second variety 

 is like the quartzite of Budleigh Salterton, the Lickey, and Harts- 

 hill. Orlhis rediix, var. Bicdleighetisis, Spirifcra Venictiilii and other 

 species have been obtained from the Bunter Beds and from the 

 Drift. These fossiliferous pebbles belong to rocks of the age 

 of the Arenig, Bala, and May Hill series, as well as to Devonian 

 rocks.- Pebbles and fossils from the Carboniferous Limestone 

 occur also in the Conglomerates. The distant origin of the Bunter 

 pebbles has been opposed on the ground that the pebbles become 

 fewer, and ultimately disappear when traced northward ; and Mr. 

 W. J. Harrison has shown that they were most likely derived 

 from land-surfaces of old rocks which existed in the Midland 

 Counties in Pre-Triassic times, and some of which have been 

 denuded and buried up beneath more recent accumulations.^ 



The Pebble-beds form a broad band of country in the neigh- 

 bourhood of Sherwood Forest, east of Mansfield, and near Retford 

 and Tickhill. As Mr. Aveline observes, it is owing to its poor 

 sandy and gravelly soil that the Forest of Sherwood existed so 

 long, the greater part being still retained as woodland or common. 

 Market Drayton stands on the Pebble-beds, there represented by 

 hard pebbly sandstone. 



In the neighbourhood of Liverpool, Manchester, and Stockport, 

 the Pebble-beds are represented by reddish-brown pebbly sand- 

 stone, largely quarried for building-purposes. Chester Cathedral 

 was largely constructed of this stone from the neighbourhood of 

 Chester. The Mersey Tunnel was to a large extent excavated 

 through these Pebble-beds, which are here characterized by the 

 rarity of pebbles.* 



The Upper Red and Mottled Sandstone, both in structure and 

 composition, appears to be the most uniform division of the 

 Bunter. In the neighbourhood of Birkenhead, Liverpool, and 

 Ormskirk, the lower portion of this subdivision is red, the upper 

 yellow, and it is sometimes sufficiently hard for building-purposes. 

 The apparent unconformity that has been noticed between the 



^ Triassic and Permian Rocks, p. 30. 



2 See Rev. P. B. Brodie, Q. J. xxiii. 210 ; S. G. Perceval, G. Mag. 1878, p. 

 333 ; J- H. Jennings, Ibid. 239 ; T. G. Bonney, Ibid. 428, 1 880, p. 404, 1883, 

 p. 199; W. Molyneux, Pioc. Dudley Geol. Soc. iii. 139. 



^ Proc. Birmingham Philosoph. Inst. iii. 157 ; Midland Naturalist, viii. 194. 



* C. E. De Ranee, Proc. Geol. Assoc, vii. 324 : T. M. Reade, Proc. Liverpool 

 G. S. 1885. 



15 



