Fbbbuary 14, 1913] 



SCIENCE 



239 



cently emphasized by Hobbs, would brush 

 the snow toward the borders of the field 

 and so tend to reduce the surface slope of 

 the interior. 



Shaekelton found that the great outlet 

 glacier in Antarctica, named the Beard- 

 more, had a rise of 80 feet per mile for 100 

 miles, with declining rate inland, attaining 

 about 11,000 feet in 275 miles, or 40 feet 

 per mile for the entire distance. If we as- 

 sume a slope of 60 feet per mile for the 

 glacier surface over western New York it 

 gives an altitude of over 9,000 feet on the 

 area of Lake Ontario, the margin of the ice 

 sheet lying at near 2,000 feet altitude. 

 Over central New York (district of Oneida 

 Lake) the altitude would be about the 

 same ; and if to this we add 30 feet per mile 

 to the middle of the Adirondacks it gives 

 3,000 feet more, or over 12,000 feet altitude. 

 If we assume 40 feet per mile on the Hud- 

 son-Champlain meridian it gives 12,500 

 feet of ice on the Canadian boundary. 

 Thirty feet per mile gives over 9,000 feet 

 of ice. These figures may be somewhat ex- 

 cessive, but they at least prove the fact of 

 a great thickness of solid water piled over 

 the state. The effect of such weight will be 

 noted later. 



The ice mass had a spreading or radial 

 flow, as a plastic body, due to its own 

 weight. The prevailing direction over 

 New York was southwestward, except that 

 in the lower Hudson Valley the flow was 

 southward, conforming to the valley. The 

 waning or thinning ice sheet was deflected 

 by the larger topographic relief, and when 

 the ice mass resting over the Ontario basin 

 ceased to be impelled by thrust from the 

 northeast it developed a spreading flow, 

 radiating from the area now occupied by 

 Lake Ontario. This is well shown by the 

 orientation of the drumlins in the Ontario 

 basin. A good illustration of valley diver- 

 sion is shown in the maps, depicting how 



the Hudson lobe and the Ontario lobe 

 pushed into the Mohawk Valley from op- 

 posite directions, impounding glacial 

 waters between them. As the direction of 

 flow near the margin of the ice sheet must 

 incline to right angle, or normal to the ice 

 front, the direction of latest movement in 

 any district can be approximately known 

 if the ice limit is determined. The series 

 of maps accompanying this writing show 

 several stages in the waning and disappear- 

 ance of the ice and suggest the direction of 

 flow at different positions. 



The set of maps gives fifteen positions of 

 the ice front during its recession across the 

 state. A larger number could be depicted, 

 but only those have been selected which 

 have some significance in the lake and 

 drainage history. The criteria used in lo- 

 cating the ice front positions are the mo- 

 raines and the ice-border river channels, 

 the latter correlating with lake levels and 

 shore features. 



The recession of the ice front was cer- 

 tainly not steady or continuous, but must 

 have had considerable oscillation, read- 

 vances and reretreats. The heavier belts 

 of moraine and the lines of long-lived ice- 

 border drainage probably represent read- 

 vanced positions. 



The length of time represented by the 

 passage of the ice front across New York is 

 unknown, but is certainly scores of thou- 

 sands of years. Probably 100,000 years is 

 not too long. We may not judge the rate 

 of waning by the present behavior ©f the 

 ice fronts in Greenland and Antarctica, as 

 the climatic factors due to differeace of 

 latitude must have been effective. If the 

 oscillations of the ice front were due to any 

 irregular or nonperiodic variations of cli- 

 mate, then we can have no idea of the time 

 involved either in the advance or the wan- 

 ing of the ice sheet. And the only period- 

 icity in climatic factors now recognized 



