MctamorpJiisin of Glacial Deposits 



7 



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 accumu- 

 lated rubbish may contain constituents previously weathered, it is 

 possible that deoxidation also takes place. 



Throughout the distance between the Mohawk Valley in New 

 York state and Michigan at the western end of Lake Erie, lime- 

 stone formations come to the surface. These outcrops suffered 

 degradation by the ice-sheet. Other limestone horizons farther 

 north, in part of this distance, also contributed to the glacial load 

 of debris. This content of limestone in glacial sediments was partly 

 dissolved even bv the cold water; no rock- forming constituent is 



Fig. 3. — Disturbed and faulted liluish till exposed along Dugway Pirook, Cleveland. 



more easily affected by water. The resulting carbonated water 

 actively attacked the silicate minerals at least. Solution and later 

 precipitation is always an accompaniment of ground-water circulat- 

 ing through glacial sediments, and further reactions will give dif- 

 ferent solutions. 



The decomposition of rock-constituents is usually accompani- 

 ed by hydration. This is almost invariably the case in oxidation 

 and carbonation. In unconsolidated materials beneath an ice-cap 

 hydration would be an active agent in alteration. 



8 Chamberlin and Salisbury, Geology, vol. 1 (1904), p. 26.3. 



