KETTLES IN GLACIAL LAKE DELTAS 595 
shore currents with the detritus-bearing stream currents. On 
the lakeward side they are usually bounded by a spit or bar 
formed transverse to the stream current. Some of the larger 
and more irregular depressions are bounded landward by the 
original surface of the valley border, but such are more likely 
to be open on the side away from the delta-forming stream. 
Dee eee eee ee 
Kettle in Delta at Potter, N. Y. General view, looking northwest from opposite 
side of Flint Creek Valley. 
Those which are confidently referred to aqueous forces occur 
below the water plane, or are surely subaqueous. 
Professor Chamberlin in discussing ‘‘kettles,” in 1877, sug- 
gested four possible methods of origin: (1) Irregularities of 
deposition or heaping of the drift ; (2) the pushing of one drift 
ridge unconformably against a preceding onc; (3)iethte incor 
poration of ice-blocks; and (4) under-drainage. To this 
enumeration the writer would add a fifth method, (5) circum- 
deposition, by capricious stream currents in the face of wave 
action, or deficient filling on delta terraces. 
