208 W. Upham — Recent Fossils near Boston. 



ern part of this belt and are fast retreating in Alaska.* The 

 last 5*00 or 1,000 years, according to Russell, have been marked 

 by rapid glacial recession in the St. Elias region. But during 

 the same or a longer time the North Atlantic area has been 

 growing colder, gradually excluding the southern mollusks, 

 causing the ice-sheet of Greenland to increase again, and giv- 

 ing to that country a much less hospitable climate than during 

 the prosperous period of the Norse colonies, from 900 to 500 

 years ago. Both the decrease of the Alaskan glaciers and the 

 increase of cold and of ice accumulation in Greenland are 

 attributable, as I believe, to the present partial closure of the 

 passage between the Arctic and Pacific Oceans. 



In another way, however, which is perhaps more probable, 

 that is, by assuming that the principal current through the 

 formerly enlarged "Bering Strait flowed as now northward, we 

 may almost equally well explain the climatic changes of both 

 the western Cordilleran belt and the North Atlantic area. 

 Such increased northward outflow from the Pacific would be 

 subtracted from the warm Kuro Si wo or Japan current, the 

 greater part of which passes to the east and south along the 

 shores of Alaska, British Columbia, and the Pacific States, and 

 would thus tend to produce the cold of the recent Cordilleran 

 glaciation. The formerly large branch of the Japan current 

 entering the Arctic Ocean by Bering Strait would be partly, 

 and probably almost wholly, carried thence eastward along the 

 northern coast of North America and through its archipelago 

 to Baffin Bay, Davis Strait, and the North Atlantic, bringing 

 somewhat milder climatic conditions to Greenland and to all 

 those shores where the colonies of southern marine mollusks 

 are known. With the subsequent decrease of the size of Ber- 

 ing Strait, during the past 1,000 years, sending more of the 

 Japan current to our Pacific coast, the Cordilleran and Alaskan 

 glaciers would be melted away or greatly reduced, as to-day, 

 but Greenland and the North Atlantic area would become 

 colder, as seems to be well proved within the present historic 

 period. 



To the same very late date we must assign the extinction of 

 the southern molluscan species on the eastern coast of New 

 England and the southern coast of New Brunswick and Nova 

 Scotia. During the time of accumulation of the aboriginal 

 shell-heaps or kjokken-moddings of Maine, and even within the 



*I. C. Russell, Geological History of Lake Lahontan, U. S. Geol. Survey, 

 Monograph xi, 1885, p. 273; Bulletin, G. S. A., vol. i, 1890, p. 142; Expedition 

 to Mount St. Elias, Alaska. National Geographic Magazine, vol. iii, 1891, pp. 64, 

 93. 98, 100, 104, 112, 173. G. F. Becker, Bulletin, G. S. A., vol. ii, 1891, p. 196. 

 Warren Upham, this Journal, III, vol. xli, pp. 41, 51, Jan., 1891 ; Am. Geologist, 

 vol: viii, p. 150, Sept., 1891. 



