524 LOCAL OR UNDERLYING DETRITUS OF THE NORTHERN DRIFT REGION. 



latter point is established, by the remains of land and fluviatile animals accompanying 

 the detritus of eastern rocks. These observations will afford the reader a general view 

 of the subject ; and while perusing the following details he must bear in mind that a 

 large portion of the centre of the map was under water after the other parts had been 

 raised above it. This recently submerged tract includes the eastern parts of Lancashire, 

 nearly all Cheshire, the north of Shropshire, and large portions of Staffordshire, Wor- 

 cestershire and Gloucestershire, being the region coloured as New Red Sandstone. 

 In proving that these districts were under the sea, while Siluria and Wales on the one 

 side, and a portion of England on the other, were above it, we assume that the sub- 

 marine tract had towards the north the form of a great bay, which tapering towards 

 the south, terminated in a strait. It is specially to the central and southern parts of 

 this space, that I now proceed to call attention 1 . 



Local or underlying Detritus of the region overspread by the Northern Drift. 



The subsoil of two thirds of the tract in question consists of rocks of the New Red 

 System. The oldest strata (with the exceptions near Dudley and Tortworth) belong to 

 the carboniferous series, which, when heaved up through the New Red Sandstone, oc- 

 casioned, at various points, a vast destruction of solid matter. (See illustrations in 

 chapters 36 and 37.) 



The consideration of this local detritus will be brief, for its composition and 

 structure lead us to suppose, that it must have been accumulated beneath the sea or 

 in estuaries, in the same manner as the coal measure detritus described in the last 

 chapter, and possibly at the same period. The surfaces of the Salopian and Staffordshire 

 coal-fields present, indeed, very generally, the same phenomena ; vast masses of the 

 New Red Sandstone with which they were once covered having been broken up and 

 distributed in irregular mounds of fine sand and gravel. Sometimes the fine sand 

 predominates ; but more often is intermixed with shingle-like gravel, both coarse 

 and fine, derived from the New Red Sandstone and adjacent rocks. In certain parts, 

 rounded quartz pebbles alone prevail ; in others, vast masses of clay inosculate with 

 beds of sand and gravel. Everywhere, however, the deposits clearly prove, that their 

 materials were derived from the neighbourhood of the localities where they are now 

 accumulated. Taking, for example, the tract surrounding Dudley, and examining into 

 the composition of the oldest or local detritus, we immediately perceive, that it must 

 have been principally produced by the upheaval of the carboniferous strata through the 

 overlying red sandstone j for it contains great quantities of the latter in a triturated 

 state, also rounded pebbles of quartz, derived from the disintegration of the conglome- 



1 The present relative levels of land are so prodigiously changed since the early condition of the region, that 

 some of the tracts containing recent shells on the surface are upwards of 1700 feet above the sea, while adja- 

 cent Silurian tracts elevated at much earlier periods, now lie at very low levels. 



