BOUNDARY OF THE GLACIATED AREA. 179 



sheet, and the only ice-masses were small areas of local glaciers 

 which did not cover two per cent of the mountain country. 



Supposing the arctic land configuration to be as now, and 

 a new oscillation of climate to bring on the conditions of a 

 glacial period, it is certain that the present ice-masses would 

 form the nuclei of new northern ice-fields, and Greenland 

 would probably be the point from which the glaciers would 

 move southward to cover eastern America ; and the absolute 

 distance from such a center would have something to do with 

 the failure of the ice to override the Cordilleras. Dawson's 

 suggestion of a great center of dispersion in Alaska, where an 

 elevated and broad highland fronts the moisture-laden ocean- 

 wind, has, it seems to me, a high degree of probability in ac- 

 counting for the southerly-moving ice of British Columbia with- 

 out recourse to that refuge of pure imagination, a polar cap.* 



With this agrees the testimony of Mr. I. C. Russell, in 

 his report on the " Quaternary Histoiw of Mono Valley, 

 California," the advance sheets of which I have been kindly 

 permitted to see. He writes : 



The Sierra Nevada during the Glacial epoch was covered by 

 an immense neve field, which probably stretched continuously 

 from a little north of latitude 36° nearly to latitude 40°. The 

 width of this belt of perpetual snow must have been irregular, 

 conforming to the present topography of the summit of the 

 range, hut it probably had an average width of between ten 

 and fifteen miles. From beneath this snowy mantle trunk gla- 

 ciers flowed both east and west down the flanks of the range. 



The evidence is such as abundantly to justify the conclu- 

 sion that the ancient glacial system of the Sierra Nevada was 

 local, and had no connection with a northern ice-sheet. The 

 glaciers were clustered about and radiated from the higher por- 

 tion of the range in the same manner as from the contempo- 

 rary neve fields of the Wahsatch and Uintah Mountains, f 



* " Systematic Geology " in the " United States Geological Exploration of 

 the Fortieth Parallel," 1878, pp. 459-461, 464. 



+ See the " Eighth Annual Report of the United States Geological Survey," 

 pp. 327, 328. 



