Upham.] 
234 
[April 17, 
noted a second boulder (6), of nearly the same size, wholly enclosed 
within the underlying sand layer ; but I saw no other boulders en- 
closed within the modified drift of this whole section, excepting in the 
very coarse bed already described, which continues northward from 
the intercalated southern mass of the underlying till, and with 
which these two boulders are closely associated. The one first men- 
tioned was evidently deposited slightly later, and the other slightly 
earlier than the principal bed of boulders and gravel ; and this bed 
seems clearly to have been formed contemporaneously with the till 
into which it merges. Indeed, my study of the two strata of modi- 
fied drift at the south, the tongue-like deposit of till between them, 
and its prolongation in the layer of coarse gravel with boulders, 
convinces me that they were rapidly accumulated in the order and 
place where they now lie, with no considerable interval between the 
deposition of the lower sand stratum and the till above it, nor be- 
tween that till and the upper stratum of the modified drift, the three 
together representing only the time that was occupied in the for- 
mation of the single stratum of modified drift into which these three 
deposits unite toward the north. 
From this conclusion others are immediately suggested, namely, 
that the whole drumlin of Fourth Cliff was probably deposited some- 
what rapidly ; that the conditions leading to the accumulation of 
the basal till were followed by such as caused the modified drift to 
be spread over it, the latter perhaps requiring no longer time than 
a single summer or the portion of the year attended by abundant 
ice-melting ; and' that conditions again ensued favoring the accumu- 
lation of till, which was thenceforward uninterrupted until the for- 
mation of the hill was completed and the overlying ice was melted 
away. Excepting the one place described, no other evidence of 
interbedding or gradual transition was seen, but the till beneath, 
like that above, is separated from the modified drift by a well de- 
fined line with which the obscure lamination of the till and the bed- 
ding of the sand and gravel are parallel. No evidence of erosion, 
nor of tumultuous pushing forward, was anywhere seen ; but in- 
stead the whole section appears to represent continuous deposition. 
The very hard and compact condition of the till, and its character- 
istic flakiness, which I have spoken of as lamination, both below 
and above the modified drift, indicate that it was deposited as a 
ground moraine beneath the pressure of the ice-sheet, instead of as 
englacial till falling loosely from the ice when it melted. It is, in 
