THE 



POPULAR SCIENCE 

 MONTHLY. 



NOVEMBER, 1886. 



NORTH AMERICA IN THE ICE PERIOD. 



By JOHN S. NEWBERRY, 



PROFESSOR OF GEOLOGY AND PALEONTOLOGY IN COLUMBIA COLLEGE. 



ALTHOUGH the glaciated area on our continent has been as yet 

 but partially explored, abundant proof has been gained, as it 

 seems to me, of the truth of the following propositions, viz. : 



1. That glaciers once covered most of the elevated portions of the 

 mountain-belts in the West as far south as the thirty-sixth parallel, 

 and all the eastern half of the continent to the fortieth parallel of 

 latitude. 



2. That the ancient glaciers which occupied the area described were 

 not produced by local causes, but were the exponents of a general cli- 

 matic condition. 



3. That they could not have been the effect of a warm climate and 

 an abundant precipitation of moisture, but were the results of a gen- 

 eral depression of temperature, and therefore afford proof of the truth 

 of what is called the glacial theory. 



The facts and arguments which sustain these propositions may be 

 briefly summarized as follows : 



The glaciation of the Sierra Nevada is general and very striking. 

 It has been studied by Whitney, King, Brewer, Le Conte, and others, 

 including the writer, who have given abundant proof that all the high- 

 est portions of the range were once covered with snow-fields, and that 

 glaciers flowed from these down the valleys on either side. Mount 

 Shasta once bore many great glaciers, of which miniature representa- 

 tives still remain ; the Cascade Mountains exhibit, perhaps, the most 

 impressive record of ice - action known ; all the higher portions of 

 the range are planed and furrowed by glaciers which descended into 

 the valley of the Des Chutes on the east, and the Willamette on the 

 west, as shown by my observations in 1855, at least twenty-five hun- 

 VOL. xxx. — ] 



