1890 .] 
453 
[Upham* 
in the Alps, Pyrenees, Caucasus, and Himalayas ; but no large 
portion of Asia is known to have been overspread by ice. 
The most anomalous feature of the accumulation of these ice- 
sheets was their absence from Siberia and northern Alaska, while 
so heavily massed in the same and more southern latitudes of 
British America, the northern United States, the British Isles, and 
northwestern Europe. Within the past year Dali’s observations 
of the absence of drift over large portions of Alaska have been 
confirmed and extended by the explorations of Russell and Mc- 
Connell, whose communications read last week before the Geo- 
logical Society of America define the limits of our glaciated area 
by a line that crosses the upper Yukon in British America near 
1st. 62° N., long. 135° W., and thence extends northward to the 
Arctic ocean somewhat west of the mouth of the Mackenzie. Rus- 
sell also states that no glaciers now exist on the mountains of 
Alaska north of the Yukon, though they are grandly developed 
on the south along the high ranges of the Pacific coast. Prob- 
ably the study of the present climate of that country will contri- 
bute much toward explaining why the ice-sheet failed to extend 
over the lower Yukon region, and will herewith help greatly to- 
ward the solution of the broader and very complex problem of the 
whole earth’s climatic conditions during the ice age 
But the course of the southern glacial boundary in the United 
States shows important points of resemblance between the climate 
of the glacial period and that of the present time. Where rainfall 
now is deficient in the interior, on the arid plains east of the 
Rocky mountains, the precipitation of snow in the Ice age was 
similarly deficient, causing the great northward deflection of the 
ice-margin from the latitude of St. Louis to that of Bismark ; and 
Dana has shown that the driftless area of Wisconsin now receives 
less rainfall than the contiguous regions that were ice-covered. 
The courses of storms and precipitation of moisture having been 
thus nearly the same as now, the great accumulations of ice on 
the continents bordering the North Atlantic suggests that a large 
element in the causation of the cold was probably a subsidence of 
the Isthmus of Panama, allowing the equatorial oceanic current 
to pass west into the Pacific, instead of being turned northward 
in the warm Gulf Stream. 
To this cause of the refrigeration of climate upon the glaciated 
portions of the globe, we may add the influence of their elevation 
