TWO GLACIAL STAGES IN ALASKA 749 



All attempts to map the limits of glaciation in Alaska have been 

 made upon the assumption that the ice reached its greatest exten- 

 sion during the last great glacial advance, the evidence of which is 

 so conspicuous, and that the limits of glaciation as shown are the 

 limits reached by the ice during this period of expansion. Up to the 

 present time no facts had been obtained which would show the age 

 of this last great ice advance, as compared with any of the various 

 stages of continental glaciation. Furthermore, although by analogy 

 one might expect that the glaciers of Alaska would have been influ- 

 enced by the same general climatic conditions which affected the 

 main body of the continent, and would have advanced and retreated 

 contemporaneously with the continental glaciers, yet for a period 

 of fifteen years, during each summer of which geologists have 

 been in the field observing glacial phenomena, the problem of 

 whether or not there have been recurrent glacial stages in Alaska 

 has continued to present many uncertainties. In 1890, and again 

 in 1891, I. C. Russell^ observed on the southern slopes of Mount 

 St. Elias certain elevated marine deposits of fine clastic sediments 

 containing bowlders which he believed to be of glacial origin. The 

 same terrane was observed, in 1913, by A. G. Maddren^ in the 

 Yakataga district, and his interpretation of the origin of the bowlders 

 is in agreement with that of Russell. The pubHshed literature for 

 the most part, however, fails to discuss the probability of earlier 

 stages of glaciation in Alaska, although the writer^ has suggested 

 that there may have been earlier glacial advances, but if so, they 

 were less extensive than the last, and the traces of such glacial ad- 

 vances were destroyed or obscured by the more extensive and more 

 recent ice invasion. 



During a geologic reconnaissance trip into the White River 

 basin, in the summer of 1914, observations were made which seem 

 to throw light both upon the age of the last great ice advance and 



^I. C. Russell, "An Expedition to Mount St. Elias," Nat. Geog. Magazine, III 

 (1891), 170-73; also "Second Expedition to Mount St. Elias in 1891," 13th Ann. Rept. 

 U.S. Geol. Survey, Part II (1893), pp. 24-26. 



' A. G. Maddren, "Mineral Deposits of the Yakataga District," U.S. Survey Geol. 

 Bull, sgz, 1914, pp. 131-32. 



3S. R. Capps, "The Bonnifield Region, Alaska," U.S. Geol. Survey Bull. 501, 

 1912, pp. 35-36. 



