H. L. FALRCHLLD PLEISTOCENE GEOLOGY OF NEW YORK STATE 



ence in latitude must be an important factor. The border of onr ice- 

 field, in latitude 41 to 44 degrees, was subjected to so much greater solar 

 radiation and consequent higher temperatures, with heavy precipitation 

 and rains, that it must have had increased plasticity and resultant mo- 

 bility, giving the surface slope diminished gradient. But, on the other 

 hand, the snow supply over the central area or alimentation ground of 

 the ice-field must have been greater than over the polar fields, which 

 might give greater depth and steeper gradients toward the interior of the 

 field. The anticvelonic winds over the ice-cap, recently emphasized by 

 Hobbs. would brush the snow toward the borders of the field and so tend 

 to reduce the surface slope of the interior. 



Shackleton found that the great outlet glacier in Antarctica, named 

 the Beardmore. had a rise of 60 feet per mile for 100 miles, with declin- 

 ing rate inland, attaining about 11,000 feet in 2 To miles, or 40 feet per 

 mile for the entire distance. If we assume a slope of 60 feet per mile 

 for the glacier surface over western Xew York, it gives an altitude of 

 over 9,000 feet on the area of Lake Ontario, the margin of the ice-sheet 

 lving at near 2.000 feet altitude. Over central Xew 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 

 Hudson-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 fig- 

 ures may be somewhat excessive, 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. 



MOVEMENT 



The ice-mass had a spreading or radial flow, as a plastic body, due to 

 its own weight. The prevailing direction over Xew York was south- 

 ward, except that in the lower Hudson Valley the flow was southward, 

 conforming to the valley. The waning or thinning ice-sheet was de- 

 flected by the larger topographic relief, and when the ice-mass resting 

 over the Ontario Basin ceased to be impelled by thrust from the north- 

 east it developed a spreading flow, radiating from the area dow occupied 

 by Lake Ontario. This is well shown by the orientation of the dnimlins 

 in the Ontario Basin. A good illustration of valley diversion is shown 

 in the maps depicting how the Hudson lobe and the Ontario lobe pushed 

 into the Mohawk Valley from opposite directions, impounding glacial 

 waters between them. As the direction of flow near the margin of the 



