i«83. 15Y Trans. N. V. Ac. Sci. 



While the phenomena described above are unmistakable, and con- 

 stitute an indisputable record of the prevalence of ice-sheets over 

 great areas of our continent, much speculation has been lavished upon 

 the possible causes of such accumulations of ice and snow as have here 

 left their marks. In a voluminous and elaborate review of the subject 

 recently published by Prof. J. D. Whitney, the glacial record is mis- 

 represented and belittled. By this author it is stated that ice has little 

 or no eroding power, while every one who has traveled through the 

 glaciated areas has noticed the peculiar impress left upon the topo- 

 graphy by the old glaciers ; and the sheet of drift material now remain- 

 ing, as the result of ice-erosion, — over one area, 2,000 miles long and 

 500 miles wide, from 30 to 50 feet thick — is in itself a sufficient answer 

 to this assertion. 



But our drift deposits are only a remnant of the mass of material 

 eroded by the glaciers. Most of the flour they ground — the clay — has 

 been washed away, and, over great areas, only the bran — gravel, sand 

 and boulders — remains. All the streams flowing from glaciers are 

 turbid with sediment supplied by the grinding of rocks by ice. This 

 has been measured in some cases, and the erosive power of glaciers 

 has then been not only demonstrated but quantitatively determined ; 

 for example, the daily transport of sediment from the Aar glaciers in 

 August is 280 tons, and Helland states that 69,000 cubic meters of 

 solid rock are annually worn away by the Justedal glacier of Norway 

 (Geikie) ; and yet we are told that ice has little or no eroding power ! 



By Professor Whitney the few glaciers, of which the record cannot 

 be ignored or sophisticated, are considered as the product of local 

 causes, and not as evidence of an ice period, which it is the great object 

 of his book to disprove. The immense extent, however, of the glaciated 

 area, reaching as it does, from the Atlantic to the Pacific, from the 36th 

 parallel northward on high lands, and the 40th on low lands, as well as 

 the evidence of appro.ximate or exact synchronism in the phenomena, 

 make it impossible to accept the theory of local causes. 



We are in fact driven to the necessity of referring the record to a 

 general climatic condition. What this condition was, is the next point 

 for investigation ; its cause or causes still another. Professor Whitney, 

 following Lecoq and others, claims that since snow and ice are mois- 

 ture evaporated elsewhere by heat, the extension of glaciers at any time' 

 or place is simply an effect of increased heat and not cold ; and hence 

 if there ever was an ice period — meaning a time when glaciers were 

 more widespread than now — it must have been a warmer period than 

 the present, with more copious precipitation. Only a few of many facts 

 need.be cited to show that this theory is untenable. First, glaciers are 

 now confined to altitudes and latitudes, where the temperatureis low — 



