

196 



INTER-GLACIAL PERIODS. 



[Ch. X. 



independent striae, but have subsequently suffered a new stri- 

 ation which is parallel and persistent across them all. These 

 appearances have been observed on the shores of the Firth 

 of Forth, below Edinburgh, and in other places, both on 

 the east and west coasts of Scotland, and on the shores of 

 the Sol way in England. Some examples of this second stria- 

 tum may have been due to the friction of icebergs on the 

 bed of the sea during a period of submergence ; others to 



a 



second advance of land glaciers over moraines of older date.* 



M. Morlot and others have adduced abundant evidence of 



two glacial periods in the Alps, during the first of which the 



glaciers attained colossal dimensions, filling the great valley 

 of Switzerland with ice, which reached from the Alps to the 

 Jura, while on the southern side of the great chain other 

 contemporaneous glaciers invaded the plains of the Po, where 



they have left moraines of truly gigantic dimensions. After 



these huge glaciers had retreated for a time, they advanced 

 again, but on a smaller scale, though still vastly exceeding 

 in size the largest Swiss glaciers of our day. The interval 

 of milder weather, marked by the decrease of snow and ice 



in the Alps, has been called by Prof. Heer the Inter-glacial 



Period, which must have been of considerable duration, for it 

 gave time for the accumulation of dense beds of lignite, like 

 those at Diirnten and other localities near Zurich. During this 

 intercalated series of warmer seasons the climate is supposed 

 by Heer to have closely resembled that now experienced in 

 Switzerland. He infers this from the fossil flora of the lignite, 

 especially from the cones of the Scotch and spruce firs, and 

 the leaves of the ash and yew, all of living species, as well as 

 from the seeds of certain marsh plants. The insects also, and 

 the freshwater shells, tell the same tale. Among the mammalia 

 occurring in the same carbonaceous shales are an elephant 

 (E. aniiquus), an extinct species of bear (Ursus spelceus), and 

 a rhinoceros different from B. tichorhinus. That the forma- 

 tion of the shale and lijmite containing the above-mentioned 

 remains was preceded and followed by periods of greater 

 cold, is shown by the polished and striated rock surfaces on 



* A. Geikie, Phenomena 

 Drift of Scotland, p. 66, 



of Glacial Messrs. C. Maclaren, Hugh Miller, 

 who cites Milne-Home, and Smith of Jordan-hill. 







5 1 





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