510 



LOCAL DRIFT OF SILURIA. 



Of this drift, the region contained in the map presents three distinct varieties, two 

 of which may be termed local, the third foreign or transported from a distance. The 

 drift of the high lands of Siluria is of the earliest date, and was produced by the ele- 

 vation of the older rocks. The next in age arose from the upcasts of the various coal- 

 fields, and the third or most modern drift is that, which covers large portions of the 

 central counties and contains bowlders of northern granite. All this detritus was accu- 

 mulated beneath the sea during successive epochs. 



The local drifts will be first described, and the most recent or northern drift will 

 chiefly occupy the next chapter. It will, however, then be shown, that the far trans- 

 ported detritus, though generally overlying, is sometimes mixed up with, and not easily 

 separable from, the local debris. 



f The second class of alluvia includes all the deposits formed in lakes and river courses, 

 since the final elevation of the districts from beneath the sea ; also the masses of tra- 

 vestine formed by calcareous springs, and the various results of atmospheric action. 



These phenomena will be described in two other chapters, after the submarine drifts 

 have been disposed of ; though for the sake of illustration, some examples of the two 

 classes will be occasionally considered together. 



Local Drift within the region of Siluria. 



All the loose detritus which covers the surface of large tracts in South Salop, the 

 north-west of Worcestershire, the whole of Herefordshire, and the adjoining Welsh 

 counties, may be called local ; because it has been derived, either from mountains 

 forming the north-western limits of the country, or from the disintegration of rocks, 

 occupying the very districts where the materials are found. 



This region, therefore, being free from all distantly transported detritus, presents a 

 class of phenomena distinct from that which is exhibited in those parts of the kingdom, 

 where the surface is covered by accumulations of materials derived from remote 

 countries. 



Now, as the drifted matter is of local origin, so we conclude that the action of the 

 bodies of water which produced it, must also have been local, and totally unconnected 

 with any vast or general deluge, even confining the application of the word " general' 5 

 to a small portion of Europe. 



Another important inference derived from the phenomena connected with this drift, 

 is, that the high combs, as well as valleys in which it abounds, must have been per- 

 manently under water ; for it is plain, that they could have been modelled into their 

 actual forms only, by the action of a large body of water overspreading their entire 

 area ; and this mass of water could not have existed unless the valleys were then beneath 



