PAST GEOGRAPHICAL MUTATIONS 13 



for by glaciation alone, or embraced by Post-Glacial 

 time. Of one thing we may be pretty certain, that 

 when the penultimate inter-glacial period had attained 

 its meridian the climatal conditions (" more humid, and 

 much more equable ") of our area, and the fauna and 

 flora inhabiting it, resembled very closely those which 

 characterized later Pliocene time. It seems probable, 

 however, that the shallow North Sea of late Pliocene 

 ages had vanished, perhaps partly due to upheaval, 

 especially in the north, or marine depression, but more 

 likely, to a very great extent, silted up by the vast 

 quantities of detritus carried by the Scandinavian and 

 Scottish ice-sheets that several times swept its bed. 

 For, as Mr. Jukes-Brown xcms.v'ks {Tht; Building of the 

 British Isles, p. 426) : " a recent boring at Utrecht has 

 proved that the surface of the Pliocene deposits is more 

 than 500 feet below that part of Holland, and as the 

 Pliocene sea probably deepened northward, it is there- 

 fore hardly too much to assume that the same surface 

 lies some 100 fathoms below the present bed of the 

 North Sea between Norway and Britain, and conse- 

 quently that the upheaval necessary to convert this sea 

 into land after the Glacial Period was lOO fathoms less 

 than would have been required to effect the same result 

 in later Pliocene time." With the coming on of the 

 third glacial period, the "great submergence" of the 

 British Islands is presumed to have occurred ; but, as 

 we have already seen, this great subsidence could never 

 have taken place — and Professor Geikie himself admits 

 that there is no evidence of any such universal depres- 

 sion in Scandinavia, unless all trace has been removed 

 by succeeding glacial action, which does not seem 



