UecGee—Meridional Deflection of Ice-Streams. 391 
like manner similar estimates for different latitudes, for the 
several seasons, and for diverse directions o : 
€ relation of the factors is such, however, as to indicate 
the general law that ice-streams flowing upon plains are deflected 
loward the sides upon which effective solar accession is least. 
‘The law is modified in its action by conditions originatin 
with the formation of moraines by the ice-stream, and by con- 
ditions affecting the origin of the ice-stream itself. 
nh nature the ice-stream, after leaving its parent cafion, 
flows not upon a plain but in a trough whose walls it builds 
upon the plain. Now after its first formation the northern 
moraine must ever oppose the tendency to further deflection ; 
and moreover, with the development of the moraines the sur- 
face of the stream will diminish in convexity. In nature, too, 
some melting of the ice will surely occur, and whatever energ 
's expended in liquefaction will be diverted from mobilization ; 
and since liquefaction will occur chiefly on the south side, that 
side will be attenuated and rendered less competent to deflect 
the stream. For these four reasons will the deflection tend to 
fail of that computed. : 
_ If, however, the northern moraine be forced outward by the 
Mpinging ice, the stream will follow it and leave a e- 
tween ice and moraine on the south to be filled with supra- 
glacial debris; and whatever melting and attenuation the south 
Side suffers, will lower that side, shift the medial axis north- 
ward, and bring more than its share of debris to the southern 
a o ° 
Moraine; which thus for two reasons will tend to widen. 
compu : 
Finally, if the oscillating glacier break out of its trough, the 
trench will occur in the feebler and more strongly constrained 
horthern barrier. 
