Glacial History of New Ejigland Islands, — Upliam. 8 1 
twenty-five miles, would exhibit, if uplifted as when the river 
flowed there, a canon channeled 2,200 feet in this now submar- 
ine plain that stretches far away at each side and landward. 
With other submerged channels of a former land drainage out- 
side our present northern Atlantic coast, as made known by 
Spencer from the charts of the United States Coast Survey and 
British Admiralty, and with the equally remarkable submerged 
river valleys of California traced by Davidson to depths of 
2,000 to 5,000 feet in detailed hydrographic work for the U. S. 
Coast Survey, we have abundant evidence of a high epeirogenic 
uplift of the greater part of North America. In the Arctic 
archipelago and along our northern coasts, the preglacial eleva- 
tion occupied a prolonged period of Late Tertiary and Pleisto- 
cene time, permitting erosion of the wide channels which now 
separate islands and of wide, long, and branching fjords; but 
southward, on the coast of California and the eastern United 
States, the less extent of the channels eroded in the now sub- 
merged continental slopes, while perhaps proving by the great 
depths a higher uplift than northward, indicates its shorter dur- 
ation, as if it were a late stage of geographic extension and cul- 
mination of the previously far northern and Arctic elevation. 
Likewise on the western coast of Europe and Africa great land 
elevation before the Glacial period is known by fjords and sub- 
merged valleys. The continuation of the valley of the river 
Adour, in the sea bed of the southeast part of the Bay of Bis- 
cay, and that of the Congo, are each distinctly traced by sound- 
ings to depths exceeding 6,coo feet. 
In these epeirogenic movements, very exceptional for their 
vertical and areal range, as compared with all that we know of 
the earth's crustal movements in other geologic periods, I rec- 
ognize the cause of the equally unique Ice age, which closely 
accompanied the culmination of these uplifts and terminated 
after the land sank to its present level or lower. Large north- 
ern parts of the formerly uplifted lands, both in North America 
and Europe, having a cold and moist climate, received snowfall 
during all seasons of the year and became covered by ice-sheets 
whose borders fluctuated with secularly varying climatic condi- 
tions, until depression of the ice-burdened areas brought again 
warm summers on the borders of the ice-sheets and caused 
them at last to be melted rapidly away. 
