156 DISCUSSION OF THE DESICCATION QUESTION. 



flanks of the Sierra Nevada of the gravels which belong to the period of 

 increased precipitation, and after the present diminished rivers had worn — 

 in large part, at least — their deep but narrow channels down the sides of 

 the range, there came a time when the higher portions of the Sierra were 

 covered with accumulations of snow, from which glaciers of great size ex- 

 tended down the valleys, some of these icy masses attaining dimensions not 

 much, if at all, inferior to those of the Alps at the present day. It was 

 farther shown that these glaciers had now almost entirely disappeared, only 

 the faintest traces of ice being left in a few localities, and especially about 

 the north side of the summit of Mount Shasta, while reasons were adduced 

 for believing that this disappearance of the ice has taken place within a very 

 recent period, and most certainly since the appearance of the human race 

 in that region. In regard to the snow accumulations of the range in ques- 

 tion, it was shown that they vary greatly in amount from year to year ; and 

 that, although they never disappear entirely from the whole of the Sierra, 

 oven after the occurrence of a cycle of abnormally dry years, they some- 

 times shrink into entire insignificance, as compared with the mass of the 

 range, occupying only small sheltered nooks on the summits of the higher 

 elevations. 



With this foundation of facts, observed and studied with great care in the 

 region which was the especial field of work of the present writer for some 

 fifteen years, the attempt was made to find out how far a similar condition 

 and succession of phenomena could be traced in other regions ; and first in 

 those adjacent to the Californian Sierra ; then, later, in otliers more distant ; 

 until, finally, the inquiry extended itself so as to embrace tlic Avliole earth ; 

 and very naturally and properly, for the subject of climatic change is one 

 which cannot be discussed with satisfaction while only narrow areas are 

 under consideration, as must be evident from the nature of the phenomena 

 themselves, the climate of any one locality being the result of a complex 

 series of events, many of which have taken place at a great distance from 

 the special locality where they become sensible to the inquirer. In thus 

 extending the investigation over regions outside of California, the pres- 

 ent writer has not been obliged to depend entirely on the work of others, 

 although such has been consulted and freely used ; he has been assisted by 

 his own investigations, which at various times during the past forty years 

 have been extended over a considerable portion of North America, and have 

 also embraced the most important glaciated regions of Europe. 



