INTERGLACIAL EPOCHS. 



253 



however, was not recognised for a number of years. Mean- 

 while, Professor Bamsay had simultaneously worked out the 

 succession of changes which had obtained in North Wales 

 during the Ice Age, and showed that a period of great glaciation 

 had been succeeded by one of submergence, when the sea rose 

 to a height of 1300 feet or thereabout. This very considerable 

 submergence of the land was in turn followed by re-emergence, 

 and by the re-advance of the glaciers, which, grinding down the 

 valleys, swept out the marine deposits that had accumulated in 

 the interval of depression. 1 As it was formerly the general 

 belief that the cold of the Glacial Period in Britain and Northern 

 Europe was induced by a great elevation of the land, geologists 

 naturally assumed that the milder conditions which followed 

 were directly due to the lowering of the land, while the subse- 

 quent re-advance of the glaciers was no less reasonably inferred 

 to have been the result of a second considerable elevation. The 

 discovery made some years later that the lignites of Dtirnten 

 and other places in Switzerland were intercalated between 

 glacial deposits added very considerable strength to M. Morlot's 

 contention that the Ice Period in Switzerland had been charac- 

 terised by considerable oscillations of climate. In 1863, my 

 brother, Professor A. Geikie, described a number of sections in 

 various parts of Scotland which showed a similar intercalation 

 of freshwater beds and peat in boulder-clay. He pointed out 

 that these beds having been formed upon a land-surface, indi- 

 cated that the boulder-clay was not the result of one great 

 catastrophe, as was then generally understood in Britain, " but of 

 slow and silent, yet mighty, forces acting sometimes with long 

 pauses throughout a vast cycle of time." 2 Morlot had suggested 

 that the facts described by him in Switzerland might possibly 

 point to some cosmical cause, and was of opinion that " the idea 

 of general and periodical eras of refrigeration for our planet, 

 connected perhaps with some cosmic agency, may eventually 



1 Quart. Joum. Geol. Soc, vol. viii. p. 371. See also, by the same author, 

 The Old Glaciers of Switzerland and North Wales. 



2 " On the Phenomena of the Glacial Drift of Scotland," Trans. Glasg. Geol. 

 Soc., 1868. 



