lxxxii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [vol. lxxvi, 



gravel-mounds and banks or drumlins of boulder-clay have retained 

 what we must suppose to be their original features almost unimpaired ; 

 whereas the continuations of the same tracts, on reaching a position 

 of free and sharp drainage, break down at once into dissected 

 ground which gives the impression of comparatively long-endured 

 erosion. In fact, the Glacial deposits are, as a whole, so susceptible 

 to weathering and stream-action that their aspect at any place is a 

 measure of the violence of the attack rather than of its length ; 

 and deductions drawn from their relative condition in this respect 

 may be very misleading. It has nevertheless been ascertained, from 

 the study of the post-Glacial freshwater deposits and other pheno- 

 mena, that there have been rather wide vicissitudes of climate 

 and of sea-level since the disappearance of the ice. We know also 

 that the event is sufficiently remote to have allowed time for prac- 

 tically all the larger valle} r s of the later drainage to have been cut 

 down to base-level, or nearly so, wherever they cross the lowland 

 drift-covered tracts ; which in itself implies considerable local 

 reshaping of the ground. 



In the areas of scanty drift, the results of post-Glacial erosion are 

 practically a continuation of, and hardly separable from, the earlier 

 work of the glacial flood-waters. The Late Glacial flood- gravels and 

 outwash-fans in many of the valleys are so copious that, in most 

 tracts of low gradient, the shrunken rivers of subsequent times 

 have been unable to cut through them, and the present streams 

 meander over the old flood-plains in slightly-incised channels, the 

 valleys being now actually shallower than they were at the close of 

 the glaciation. This condition is exemplified, in varying degree, 

 in all parts of the country ; and widely, by the upper Trent and 

 its tributaries ; by that portion of the upper Severn which traverses 

 the Shropshire plain ; and by some of the rivers of the Vale of 

 York. 



Another obvious change in the surface-features since the drifts 

 were deposited is due to the obliteration of most of the pools and 

 lakelets, with which every drift-covered lowland appears to have 

 been thickly dotted upon the melting-away of the ice. In some 

 cases the hollows have been filled up with sediments ; in others they 

 have been drained by the opening of water-channels, often with 

 human aid. The sediments within them are invariably of land 

 or freshwater origin : they prove that the sea has had no part in 

 the final shaping of the interior of our country, though it has 

 meantime done much work on the coast-line, hoth by erosion and 



