iMtergLacIaL periods In ancient ice ages 359 



piling up of great delta masses of firm materials which the later ice-sheet 

 can not displace, but must climb over. 



The absence of interglacial deposits in any given region is, then, no 

 valid argument against interglacial periods. The vs^riter holds that at 

 least one interglacial period of great length and with a warm climate is 

 proved for America, and that there is evidence enough in the rest of the 

 world to suggest strongly that this interglacial period was universal. 



The evidence just given from glaciated regions is interestingly corrobo- 

 rated by climatic changes in ungiaciated regions. Doctor Gilbert's well 

 known proof of two moist periods in the history of lake Bonneville in 

 Utah, with a dry interpluvial time, corresponding to two ice ages and an 

 interglacial period, may be cited as an example of this, and also the 

 parallel case of lake Lahontan. Dr Hans Meyer brings out the same 

 facts in the Andes below glacial levels, where he finds terraces correspond- 

 ing to two pluvial, = glacial, periods.^^ 



Eeference may be made also to Mr Huntington's notable paper on 

 "Some characteristics of the glacial period in non-glaciated regions," 

 wherein he correlates the alternating times of moister and drier climates 

 in the Central Asian region with the advance and retreat of the glaciers 

 in the Asiatic mountains. He believes there is no reasonable doubt that 

 Central Asian moraines are synchronous with those of Europe." In the 

 Kalihari desert of South Africa Doctor Passarge, too, has found evidence 

 of an alternation of moist and dry climates and refers to certain sand 

 dunes as formed in interpluvial times, the equivalent of interglacial 

 periods. 



It will be seen, then, that climatic changes which have taken place in 

 non-glaciated regions strongly support the evidence for interglacial periods 

 in glaciated regions. When two different lines of research lead up to the 

 same conclusion the probability of the correctness of that conclusion is, 

 of course, very much strengthened ; so that we may safely assume that 

 interglacial periods were worldwide in Pleistocene times. 



Interglacial Periods in ancient Ice Ages 



The best known of the ancient glacial periods, that of the Permo- 

 Carboniferous, has been sufficiently studied in some regions to make it 

 worth while to look for evidence of interglacial times, and the literature 



^ In den Hoch Anden von Equador. 



s' Bulletin of the Geological Society of America, vol. 18, pp. 351-388, 



