Sub- Aqueous Differential Weathering. — Fuller. 355 
Diagrammatic Section of the Alloway Well. 
DEPTH. THICKNESS. 
580 ' 
980' 
1930 
580' 
400 ' 
950' 
FORMATION. 
Salina. 
Niagara 
and 
Clinton. 
Medina. 
Oswego sandstone 
and 
Hudson shale. 
Bottom of well. 
the Seneca Falls well, \2% miles S. E. of Alloway, 400 feet* 
as compared with the 400 feet of this well. Again in the 
Clyde well, the Medina formation is 942 feet thickf , and 950 
feet in the Alloway well. 
AN INSTANCE OF SUB-AQUEOUS DIFFERENTIAL 
WEATHERING. 
By M. L. Fuller, Mass. Inst. Tech., Boston, Mass. 
Differential weathering, by means of which the harder or 
more resistant portions of a rock are left in relief, is a com- 
mon feature of practically all rocks which are exposed to the 
action of the atmosphere. On the other hand, rocks wholly 
covered by water, except in the case of limestones, and of 
rocks exposed to the action of swamp waters, highly charged 
with decaying organic matter, rarely show evidences of such 
weathering. 
*Ibid., p. 203. 
flbid. p. 204. 
