Mctamorphisin of Glacial Deposits ir 



pressure per square foot of over 144,000 pounds. Both of these 

 computations, it is noted, are for clear ice. Knowing that the ice- 

 sheet must have carried constantly some drift, these figures under- 

 measure, perhaps, the real pressure. That the subjacent deposits 

 would be compressed by the weight of this ice is undebatable. 



Adams has shown that a condition of rock-flowage w-as in- 

 duced in marble by a pressure of about 18,000 pounds per scjuare 

 inch." The pressure on the sediments, as discussed above, is in 

 either case more than 9,000 pounds per square inch. 



Another possible factor associated with the question of pres- 

 sure is the development of heat. Even the laggard motion of an 

 ice-sheet represents energy which through basal interference is con- 

 verted into heat. This heat may have no other manifestation than 

 the wastage of ice near the friction zone. WHiether a dead load 

 upon compressible matter evolves heat in the absence of appreciable 

 movements along planes developed in this matter is a question on 

 which the writer is not informed. 



3. It is thought, furthermore, that pressures are evolved by 

 chemical changes going on in this drift. Such pressure is an accom- 

 paniment of hydration when the hydrated mineral is confined as 

 must be the 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 ^^'isconsin 

 ice readvancing over drift it had recently deposited ; faulted sedi- 

 ments subjacent to till of such a readvance are shown in fig. 7. 



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 



11 F. D. Adams, Bulletin Geological Society of America, vol. XII (1901), p. 457. 



