Trans. N. V. Ac. Set. 159 Jtifie 4, 



Everything indicates that the system of rain-bearing winds, the topo- 

 graphy, and hence the precipitation have been substantially the same 

 for a long period. But any cause which could produce a depression of 

 temperature would certainly diminish evaporation, and form lakes in 

 the valleys and glaciers on the mountains. To prove this, we have only 

 to cite the phenomena presented by summer and winter in the western 

 territories. In winter, the snow-fall on the highlands is heavy, and the 

 accumulation of moisture in this form is large. The skies are cloudy, 

 and evaporation is small. In summer, the sky is cloudless, the heat in- 

 tense, evaporation and desiccation rapid. In the spring the snows 

 melt, flood the valleys and form temporary lakes, which in midsummer 

 dry up to playas. A perpetuation of the conditions of winter and 

 spring would inevitably produce glaciers and lakes, and these would 

 be essentially synchronous. A depression of temperature, which should 

 intensify and prolong the present winter, and make midsummer like 

 the present May, would inevitably produce glaciers and lakes, in the 

 main synchronous, and thus would accomplish all that we find recorded. 

 But to intensify and prolong summer by an elevation of temperature, 

 would not produce either lakes or glaciers. 



That the ice period was cold and not warm, is further proved by the 

 prevalence of an Arctic flora and fauna on the land and in the sea, in 

 all regions near the old glaciers. The Arctic shells of the Champlain, 

 the Arctic plants in the Ouatenary clays, the reindeer, musk ox, woolly 

 mammoth and woolly rhinoceros, all tell the same undeniable story. 



From the facts cited, and others of similar import in the southern and 

 northern hemispheres, we must conclude, ist, that a glacial period has 

 prevailed simultaneously or alternately in both hemispheres ; and 2d, 

 that the glacial period or periods were periods of lower temperature 

 than that of the present day. 



An inquiry into the cause of the cold of the ice period would open a 

 question beyond the scope of this paper, and one too broad and sugges- 

 tive to be discussed to any purpose in the time at our command. I 

 may say, however, in passing, that I have elsewhere shown that no ar- 

 rangement of land and sea, consistent with the known facts of Tertiary 

 and Quaternary history, will enable us to refer that cold to any topo- 

 graphical or even telluric cause. Some extraneous influence, such as a 

 variation in the heat radiated by the sun, as suggested by Newcomb, 

 or a variation in the eccentricity of the earth's orbit, as advocated by 

 Croll, or some other cosmical cause, must be credited with effects so 

 widespread and stupendous as the ice period has left behind it. 



The Academy then adjourned to meet October i in the new 

 building of Cohnnbia College, at Forty-ninth street and Madison 

 avenue. 



