GLACIAL BOUNDARY IN OHIO. 769 
the north pole would everywhere move to the south, and so we could 
get this southerly motion from the mere accumulation of ice, without 
supposing any change of level. 
The influence of the Mississippi Valley would naturally favor the 
flow of ice in a southerly direction. But the slope from the Alleghenies 
to the Mississippi is gradual and tolerably uniform, and if the ice were 
simply adapting itself to the trough of the Mississippi, we should 
expect the curve of the southern boundary would be free from marked 
irregularities. The sudden deflections, southward, such as mark the 
line through Western Pennsylvania and Ohio, indicate another cause. 
The irregular southerly movement of ice would seem to have been due 
to irregularity in the accumulations of snow to the northward. For 
instance, if we suppose that the accumulation of ice over the State of 
Michigan and to the southward were a thousand feet in excess of that 
over Western New York and the Province of Ontario, that would pro- 
duce a great extension of the ice-current south of Michigan. The forces 
from behind causing the ice movement would distribute themselves 
somewhat as in water when stones of unequal size are dropped into it 
at places not far distant from each other. The more vigorous waves, 
produced by the larger object, would project themselves a greater 
distance beyond the line joining the centers of disturbance than those 
from the other Where these waves met they would partially counteract 
each other. Such a meeting of forces evidently is indicated by the 
sudden southerly trend of the moraine in Knox county. 
49 G. 
