Sayles — Dilemma of Paleoclimatolo gists. 4:71 



ought to be some evidence of the climate of the Pleistocene 

 in the deposits which formed ontside the glaciated areas 

 and on these, if there were no tillites or glacial slates, the 

 conclusions would be based. 



If the geologists can make out four episodes of great 

 explosive vulcanicity during the Pleistocene to correlate 

 with the four glacial episodes now recognized, the most 

 important cause for ice ages may have been found. The 

 occurrence of an interglacial ash bed at Des Moines, Iowa, 

 reported by Keyes, is interesting in this connection. In 

 any event any cause within the earth itself, which could 

 cause glacial periods, should be investigated to the utter- 

 most before we venture beyond the earth. If the sun is 

 responsible for glacial and interglacial episodes it will be 

 well-nigh impossible with our present knowledge to prove 

 it, however strong any solar theory may be. 



The finding of tillites in formations which originated 

 during times of great land emergence have led geologists 

 to infer that only at such times could the earth be cool 

 enough for glacial conditions, and that there was a causal 

 connection between mountain building and glaciation. 

 From recent discoveries of tillites deposited during times 

 of great ocean transgression it is now greatly to be ques- 

 tioned whether a large land surface is necessary for at 

 least a logical glaciation. As already pointed out, a world- 

 wide glaciation could not be registered without great land 

 masses, but local glaciation appears to have occurred dur- 

 ing the Silurian, about Niagara time, as discovered by 

 Kirk 23 in Alaska in 1917, and in the Beekmantown at 

 Levis, Quebec, as discovered more recently. Kirk found 

 a thick bed of tillite between what would appear to be 

 warm water limestones. In the Beekmantown the waters 

 Avere supposed to be warm by some and cold by others. 

 In both cases the extent of land was comparatively small 

 and the extent of marine waters was great. If there had 

 been extensive continental areas during these times it is 

 probable that great continental glaciers would have 

 formed. It is to be noted that the latitude of the Silurian 

 case is between 55°-60 c north and of the Beekmantown 

 case at Levis about 47° north. Very regularly banded 

 shales of Lower Ordovician age with marked seasonal 

 characters, collected by Mr. A. C. Swinnerton in the 

 summer of 1920 in Georgia and Tennessee, would indicate 



