THE METAMORPHISM. OF GLACIAL DEPOSITS A479 
of water. In all climates circulating ground water exists at some 
depth; the more humid the climate, the higher is the ground-water 
level. It is probable, however, that a special condition exists in 
sediments subjacent to an ice-cap; here, on account of the constant 
melting of the basal ice caused by radiation from the earth,‘ the supply 
of water is so great that a condition of saturation exists in these sedi- 
ments. This condition of saturation was certainly the case during 
both the advance and retreat of the ice-sheet within the north-sloping 
side of the St. Lawrence drainage basin. This northward slope in 
conjunction with the wall of ice caused a ponded condition of drain- 
Fic. 3.—Disturbed and faulted bluish till exposed along Dugway Brook, Cleve- 
land. ; 
age. Beneath these bordering lakes, sediments were always in a 
condition of saturation. 
Underneath an ice-sheet, it is reasonable to suppose that oxida- 
tion is subdued, but even in the absence of atmosphere, sulphides 
may be slowly changed to sulphates. Since this glacially accumulated 
rubbish may contain constituents previously weathered, it is possible 
that deoxidation also takes place. 
Throughout the distance between the Mohawk Valley in New 
t Chamberlin and Salisbury, Geology, Vol. I (1904), p. 263. 
