THE METAMORPHISM OF GLACIAL DEPOSITS 485 
case in drift subjacent to a burden of at least 9,000 pounds per square 
inch. Other chemical changes also tend to increase the bulk of the 
minerals being altered. 
SUMMARY 
In defining its age and origin the most suggestive feature of this 
drift is its color which is constant over widely separated areas. ‘The 
folding, jointing, and faulting might be caused by Wisconsin ice 
readvancing over drift it had recently deposited; faulted sediments 
subjacent to till of such a readvance are shown in Fig. 7. 
Fic. 7.—Faulted glacial gravels. Yellow till has been removed from the top. 
It is possible that the bluish till is the product of the oncoming 
Wisconsin ice. If the pressure of an ice-cap is the most active agent 
of alteration, and the time factor is secondary, it is even probable that 
both the bluish and yellow drifts are Wisconsin; but the following 
observations tend to diminish this probability: 
About three miles northeast of Newark, O., along Shanee Run, and 
again two and one-half miles southeast of Newark along Quarry Run, 
I have seen the same bluish till, at the former outcrop in contact with 
the yellow drift, at the latter showing only in the bed of the stream 
