346 G. W. Bulinan — Glacial Geology. 



Alpine lakes, tliey crept out from these and piled up great end- 

 moraines upon the lower grounds beyond." ^ 



Prof. Heer's inference as to climate is, however, somewhat incon- 

 clusive. Pine, Oak, Birch, and Larch are doubtless native trees in 

 Switzerland at the present day, but do they not occur up to such 

 heights that they might easily be mingled with the deposits of the 

 present glaciers, especially during some of those minor oscillations 

 to which these are subject ? And if those in the lignites are proved 

 to be intercalated with glacial deposits, it may not mean any more 

 than that these temperate forms of vegetation approached the ice 

 of the glacial period as nearly as the same trees approach the ice 

 of to-day. But the evidence that the growth of these trees was 

 succeeded by a glacial period is less satisfactory than that it was 

 preceded by the same. 



The lignite is surmounted by sand and gravel upon which are 

 several large alpine erratics. This is certainly suggestive, but 

 hardly sufficient; for, to quote the authors of the Manual of the 

 Geology of India, such " presumed erratics " are the " least certain 

 form " of evidence of glacial action. And in considering such the 

 enormous carrying power of Alpine torrents is perhaps too much 

 lost sight of. 



"But," says Prof. Geikie, "the erratic blocks that overlie the 

 lignite are not the only evidence of this second advance of the 

 glaciers. That the ice after retiring from the Jura to the mountain- 

 valleys did again invade the low country had been inferred before 

 the interglacial character of the lignite beds was discovered. It had 

 been known for years that the first ground-moraine and ancient 

 alluvium were overlaid by newer ground -moraines, terminal 

 moraines, and alluvium ; the meaning of this having been pointed 

 out by Morlot as far back as 1854." ^ 



The facts adduced by M. Morlot, however, can scarcely be con- 

 sidered conclusive evidence of two glacial epochs separated by a 

 prolonged warm interval. 



In his paper he speaks of two glacial periods, a general mighty 

 glaciation, and a more limited local glaciation. The evidence adduced 

 is the presence of " diluvial drift " on boulder-clay. 



" During the diluvial period," he writes, " the glaciers had entirely 

 disappeared, as has been shown, whilst after the diluvial period the 

 glaciers returned, leaving on the diluvial terraces abundant deposits."^ 



M. Morlot mentions examples of this " diluvial drift " overlaid by 

 erratics, and others of the same drift lying upon till; but he brings 

 forward no case where it lies between glacial beds, 



Ihe formation of the loess is attributed to the glacial period. 

 The evidence of the glacial origin of the loess, however, is far from 

 certain, nor is the opinion that it thus originated by any means 

 universal among geologists ; so that any argument drawn from its 

 presence on supposed interglacial beds is inconclusive. 



1 Great Ice Age, pp. 405-6. 



- Edinburgh New Philosophical Journal, 1855, p. 14. 



3 Edin. New Phil. Journ. 1855, p. 18. 



