Upliam.] 1^ fNov. i6, 
In New EiiglantI, on account of the absence or extreme rare- 
ness of any beds of modified drift which give evidence of having 
oeen covered by a re-advance of the ice, the till of the drumlins, 
according to this view, appears to have been collected into its 
present masses in the basal part of the ice-sheet, while a moflerate 
thickness, probably seldom more than 50 or 100 feet, of ice lay 
beneath. Over the drumlins a somewhat greater thickness, per- 
haps varying from 200 to 500 or 1,000 feet, of ice formed largely 
from the snowfalls of recent years or the immediately preceding 
century or more, with probably much addition from the thick 
inner part of the ice-sheet, containing from whichever source 
little or no drift, passed and molded these hills in their smoothly 
oval or round or elongated forms. 
It is thus readily seen why the amount of finally englacial drift 
upon the surface of drumlins is usually less than on intervening 
tracts of low ground and on those parts of the drift-bearing area 
from which the ice-sheet was more rapidly melted away. 
We can also understand why these accumulations are so fre- 
quently found capping the top of low hills of the bed rocks, since 
these projected through the ice that lay beneath the superglacial 
and afterward again englacial drift stratum and so were obstacles 
to favor an aggregation of that drift, either as a complete druinlin 
resting on the hill of rock, or as a lenticular slojie of till, of which 
abundant" examples are found in New Hampshire, collected on 
the stoss or the lee side of the rock hill, and occasionally in slopes 
of this form covering both these most exposed and most sheltered 
sides of the hill thickly and its intervening flanks thinly, with 
visible outcrop of the i-ock only on its summit. 
Powderhorn Hill in Chelsea, one of the largest drumlins near 
Boston, rising about 200 feet above its base, which is near the sea 
level, and having an exceptionally elongated form, with a length 
of three quarters of a mile and one fourth as great width, affords 
evidence that a slight thickness of ice remained beneath it when 
it was accumulated. Extensive excavations, from 20 to 40 feet deep, 
in each end of this drumlin consist wholly of till, with no trace 
of any bed or seam of stratified drift. In one of these sections 
about 30 feet high on the north side of its southeastern end, I ob- 
served a nearly vertical irregular course of fracture, from one to 
six inches wi<le, filled with sand and fine gravel brought by per- 
colating water, where this long hill had suffered a slight disloca 
