James Geikie — On Changes of Climate. 219 



preglacial and interglacial deposits may exist in the English valleys, 

 just as they occur in those of Scotland. In the paper referred^ to 

 above, it was further pointed out that the last excessive denudation 

 of the Scottish glacial and interglacial drifts was effected mainly 

 during the growth of the sand and gravel (kames) series. '•' During 

 that period waves and currents often ploughed out the till in the 

 narrow straits and seas to a large extent, while in the fiords and 

 other sheltered regions this deposit escaped the same degree^ of 

 erosion, and the configuration then given to it has not been oblite- 

 rated by the atmospheric forces, although these have been so long 

 employed in its reduction." I do not under-estimate the erosion by 

 frosts, rain, and rivers since the re-elevation of the land from the last 

 great submergence. It would be strange that any one familiar with 

 the aspect of our hills and -valleys should dream of doing so; the 

 later denudation has tmdoubtedly been enormous : yet I feel con- 

 vinced that upon the whole the glacial and interglacial deposits 

 of Scotland still retain much of the appearance they presented after 

 the final retreat of the sea. If we are to believe that the preglacial 

 and interglacial river-deposits of England have all been swept away, 

 and that the valley-gravels belong exclusively to postglacial times, 

 then we must also believe that the marine denudation during the last 

 great submergence and the subsequent subaerial erosion have been 

 much more excessive in England than in Scotland, and that far 

 greater physical changes have been efi'ected in the former than in 

 the latter country since the re-elevation of the land. 



Since the deposition of the older valley-gravels of England, con- 

 siderable derangement of the drainage-system has taken place. Mr. 

 Prestwich remarks, " One feature of these deposits is, that although 

 closely related to the present configuration of the surface, yet they 

 are always more or less independent of it. They are often near 

 present lines of drainage, yet could not, as a whole, possibly have 

 been formed under their operation." ^ In this respect they closely 

 resemble the Scottish interglacial beds, to which, indeed, the entire 

 description just quoted most aptly applies. It has been already 

 shown that the partial or complete filling up of the preglacial and 

 interglacial river-cuts with drift deposits has often so modified the 

 contour of the ground as to compel the streams in postglacial and 

 recent times to hollow out for themselves new cuts in drift deposits 

 and the solid rocks. In Scotland, glacial deposits are so well marked 

 that there is no possibility of their being mistaken for anything else ; 

 they tell us in language that cannot be misconstrued, that the gravels, 

 sands, silts, etc., lying in old water-courses beyond the reach of the 

 present streams are preglacial and interglacial, — we cannot by any 

 ingenuity explain away the superimposed Till. But the glacial 

 deposits of many parts of England are by no means so well defined. 

 The further we recede from the mountains of that country, the 

 glacial drifts become less and less distinguishable. To such an 

 extent is this the case, that geologists are sometimes at their wits' 

 end to say whether the large stones occasionally met with in the 

 1 Phil. Trans. 1860. 



