218 James Geikie — On Changes of Climate. 



Layer of ochreous clay. Shells, Cyclas. 



Smaller gravel. Implements. Bones and teeth of Elephas, Deer, Bos, etc. 



Limestone rock." 



It may be admitted that tlie boulders of older rocks occurring in the 

 " coarse gravel " near the base, and in the " subangular gravel " near 

 the top of this section, have been derived from the Boulder-clay 

 of the adjoining higher grounds ; yet it by no means follows that 

 the underlying bed of " smaller gravel " has had a similar origin. 

 For all that can be shown to the contrary, it may belong to a much 

 more remote antiquity than the Boulder-clay in question^ and may 

 date back to interglacial or even to preglacial times. 



It is quite certain, however, that mammal-bearing gravels have 

 been found to rest upon Boulder-clay. Mr. Prestwich put this 

 beyond all doubt by showing that at Hoxne certain freshwater beds 

 which have yielded flint implements and mammalian remains were 

 superposed on Boulder-clay. Nevertheless this does not prove that 

 these fluviatile deposits are bf post-glacial age. To make this 

 certain we should require to show that the Boulder-clay in question 

 belongs to the close of the Glacial epoch ; for what I hold is, that 

 the deposition of Boulder-clay and other glacial drifts both preceded 

 and succeeded the formation of some at least of the older valley- 

 gravels. The consideration of this point raises the wide question 

 of the age of the English valleys. Are those valleys postglacial, 

 interglacial, or preglacial ? In a former paper ' I took the liberty 

 of saying that the sequence of the glacial deposits as developed in 

 Scotland being so comparatively simple, we might with advantage 

 view this sequence as typical, and that thus we might obtain a key 

 to solve the difficulties which beset the student of the glacial accumu- 

 lations in England. We may now advance a step further in this 

 correlation of geological phenomena. Some years ago I attempted 

 to give a brief account ^ of the kind of denudation to which 

 Scotland had been subjected since glacial times, and I showed, what 

 indeed was familiar to most geologists, that its chief features were 

 impressed upon the country in ages long anterior to the advent 

 of the Glacial epoch. Here and there we find the streams flowing 

 in deep ravines which they have scooped out for themselves since 

 the deposition of the glacial drifts ; but although they may not thus 

 always flow exactly in their preglacial and interglacial channels, yet 

 nevertheless they make their way to the sea along the same great 

 lines of drainage which marked the country before the first approach 

 of glacial cold. In short, the present river-cuts are postglacial and 

 recent, but all the main valleys in which these river-cuts are made 

 existed in preglacial times. There is nothing to show that it is 

 otherwise with the valleys of England. " One thing is certain," 

 Professor Eamsay says, " that before the Glacial epoch the greater 

 contours of the country were much the same as they are now."^ 

 Such being the case, there is nothing unreasonable in supposing that 



' See Geol. Mag. for March. 



"^ See Trans. Glas. Geol. Soc, vol. iii., p. 54. 



3 Physical Geog. and Geol. of Great Britain, p. 142, 



