486 THE ICE AGE IN NORTH AMERICA. 



cumference. " In the "transition beds" of the same authors, 

 which are supposed to be of Upper Cretaceous age, there also 

 are bowlder-beds with erratic blocks of great size. 



I know of no evidence of glacial phenomena in Eocene strata 

 excepting the occurrence of huge masses of included gneiss in 

 the strata known as Flysch in Switzerland. On this question, 

 however, Swiss geologists are by no means agreed, and I attach 

 little or no importance to it as affording evidence of glacier ice. 



Neither do I know of any Miocene glacier deposits except- 

 ing those in the north of Italy, near Turin, described by the 

 late eminent geologist, Grastaldi, and which I saw under his 

 guidance. These contained many large erratic bowlders de- 

 rived from the distant Alps, which, in my opinion, were then 

 at least as lofty as or even higher than they are now, especially 

 if we consider the immense amount of denudation which they 

 underwent during Miocene, later Tertiary, and post-Tertiary 

 times.* 



In North America Professor Shaler would attribute the 

 conglomerates of Jurassic age in the valley of the Con- 

 necticut, in a part of which lie the celebrated bird-tracks, to 

 glacial origin. This he infers, from the great thickness of 

 the beds, the absence of life from the accompanying sand- 

 stones, the subangular forms of many of the pebbles, and 

 from the similarity in composition of the pebbles of that 

 conglomerate with that of those found in the modern drift 

 of the region.-)* Fpon this conclusion, however, it is proper 

 to remark that the drift in the lower Connecticut Valley 

 would, to a great extent, come from the same region, whether 

 brought by ice or water, and the extent to which the pebbles 

 would have been reduced to uniformity and smoothness by 

 attrition depends upon the distance to which they have been 

 rolled, or the length of time to which they have been sub- 

 jected to wave-action. From what appears, the evidence is 

 not clear that the fragments from which the pebbles are 



* ** Nature," vol. xxii, p. 389. 



f See " Illustrations of the Earth's Surface : Glaciers," by N. S. Shaler and 

 W. M. Davis. Boston: James R. Osgood & Co., 1881, p. 95. 



