592 HERMAN L. FAIRCHILD 
The materials composing the delta are quite variable and 
poorly assorted, containing an unusual amount of large stones 
and even boulders. This is epecially the case on the northeast 
side of the 1080 feet plateau, where several heavy stone fences 
have utilized only a portion of the field stone. These, however, 
might be wholly attributed to the powerful stream, but many 
larger and angular boulders on the slopes of the basin are not 
so explained. 
Of the origin of the kettle two hypotheses have been consid- 
ered; one, that it was a result of capricious currents and defi- 
cient filling, the other that the basin is a portion of the space 
occupied by a block of ice during the deposition of the delta. 
The first explanation was suggested by the form of the spitlike, 
sloping ridges on either side of the swamp, the location of the 
deepest part of the basin at the extreme edge of the delta, and 
by the existence, in other deltas, of smaller kettles apparently 
produced by the aqueous forces alone. This explanation is now 
thought inadequate for the Potter basin. 
During the study of this. feature correspondence was held 
with Professor J. B. Woodworth, from whom valuable sugges- 
tions have been received. The sketch and photographs were 
sent to him, and he thought the Potter phenomena similar to 
other basins which he had studied in New England, and the 
genesis of which is confidently referred to ice-blocks. The 
writer accepts this theory for the origin of the Potter basin. 
The deepest part of the basin is an oval swamp which holds 
water until removed, apparently, by evaporation. This indicates 
an impervious bottom. The depth of the vegetal accumulation 
is undetermined, but it seems probable that the original bottom 
of the kettle must have been in till or on rock, and below the 
water-laid drift. It seems improbable that such a deep hole, 
with walls so steep, could have been produced as a construc- 
tional feature in open water. If such were the case, the spitlike 
points inclusing the kettle should consist of the finest material 
brought down by the dying currents. The material, on the con- 
trary, is not sand or even fine gravel, but stony gravel, and the 
