GLACIERS AND CLIMATIC OSCILLATIONS. 26d 



land, the air has its tempei'ature increased, and thus becomes a dry wind. 

 If this explanation of the present climatic condition of the Great Basin be 

 accepted, it is evident that past fluctuations in the climate of the same 

 region could be accounted for by assuming changes of direction in the cur- 

 rents of the Pacific. 



Testimony of the Glaciers. — Thus far our discussion has been confined 

 to the evidence afforded by the records of the ancient lakes. It is mani- 

 fest that the glaciers which existed on the neighboring mountains during 

 the time the lakes were flooded should furnish additional evidence bearing 

 on the same question. 



The climatic conditions favoring the origin and growth of glaciers has 

 recently been a subject of controversy. Some writers have claimed that 

 the Glacial epoch was a warm period, in comparison with the present, and 

 that the extension of the glaciers was due to an increase of precipitation 

 caused by a greater evaporation over distant oceanic surfaces, the increased 

 evaporation being caused by a general rise of the mean annual temperature. 

 This hypothesis, we believe, was first suggested by Tyndall and Frank- 

 land, and has been extended by Professor Whitney in his work on "Climatic 

 Changes in Later Geological Times." A number of articles in various scien- 

 tific journals have also been published in extension and support of the same 

 assumption. 



It is beyond the scope of the present volume to enter into the theoret- 

 ical discussion thus opened, nor is it necessary, as the arguments brought 

 forward by the writers cited above have been controverted by Newberry, 

 Button, Gilbert, and others, who adhere to what may be called the ortho- 

 dox belief — having been held by the majority of writers on geological 

 climate — that glaciers are an index of cold, and that their great increase 

 during the Quaternary was due to a decrease in mean annual temperature. 

 In other words, the winters during the Glacial epoch were longer or more 

 severe than at present, and their snows not completely melted during the 

 short summers. The conclusions reached by these writers is so entirely in 

 accordance with all that has come under our own observation in reference 

 to the existence of glaciers, that we do not hesitate in considering their de- 

 terminations as final. The fact that the winter season in the Far West, for 

 example, is the one that favors the accumulation of snow and the growth of 



