THE GEOLOGICAL HISTORY OF NEW YORK STATE 89 
north Atlantic coast line was then considerably farther out than 
now because of the greater elevation of the land. 
Direction of movement and depth of ice in New York. The fact 
that glacial ice flows as though it were a viscous substance is well 
known from studies of present-day glaciers in the Alps, Alaska, 
or the Greenland ice sheet. A common assumption, either that the 
land at the center of accumulation must have been thousands of 
feet higher or that the ice there must have been immensely thick, 
in order to permit flowage so far out from the center, is not neces- 
sary. For instance, if one proceeds to pour viscous tar slowly in 
one place upon a perfectly smooth (level) surface, the substance 
will gradually flow out in all directions, and at no time will the 
tar at the center of accumulation be very much thicker than at 
other places. The movement of the ice from one of the great 
centers was much like this, only in the case of the glacier the 
accumulation of snow and ice was by no means confined to the 
immediate centers of accumulation. 
When the Labradorean ice sheet spread out southward as far as 
northern New York, the Adirondack mountains. stood out as a con- 
siderable obstacle in the path of the moving ice, and the tendency 
was for the current to divide into two portions, one of which passed 
southwestward up the low, broad St Lawrence valley, and the other 
due southward through the deep, narrow Champlain valley. As the 
ice kept crowding from the rear, part of the St Lawrence ice lobe 
pushed into the Ontario basin, while another portion pushed its 
way up the broad, low Black river valley and finally into the Mo- 
hawk valley. At the same time the Champlain ice lobe found its 
way into the upper Hudson valley, and sent a branch lobe up the 
broad, low Mohawk valley. The two Mohawk lobes, the one from 
the west and the other from the east, met in the Mohawk valley 
not far from Little Falls. As the ice sheet continued to push 
southward, all the lowlands of northern New York were filled, a 
tongue or lobe was sent down the Hudson valley, and finally the 
whole State, except the southern border of Long Island, was buried 
under the ice. The general direction of ice movement at this time 
of greatest ice extent was southward to southwestward with per- 
haps some undercurrents determined by the larger topographic 
features. Thus we learn that the major relief features of the State 
very largely determined the direction of ice currents, except at the 
time of maximum glaciation when only the undercurrents were 
controlled. 
These ideas are abundantly borne out by the character and dis- 
tribution-of the glacial striae and boulders over the State. Central 
