FULLER : NOTES ON A CARBONIFEROUS BOULDER TRAIN. 201 
one might expect, the lateral dying out of the boulders being far from 
gradual. 
Influence of topography on distribution. — One of the earliest 
facts brought out by the study of the boulder train under discussion 
was that the distribution to a considerable extent has been affected 
by the topography. The difference between the number of boulders 
on the stoss and top slopes of the elevations and the number on the 
lee slopes was especially marked, the number in the former case far 
exceeding that in the latter. The best example of this was noted 
on a hill about a mile northeast of Stoughton Center, some five or 
six miles southwest of Great Pond of Braintree. Commencing at 
the bottom of the valley southeast of the hill in question, I examined 
the stone-walls along the road leading northwesterly to the top of 
the hill. Notwithstanding that the slope was very gradual, I suc¬ 
ceeded in finding, in a distance of nearly a mile, less than 20 red 
boulders, while, when the top was reached, more than twice that 
number were observed in a distance of a few hundred feet. This 
points distinctly to the view so strongly maintained by Professor 
Crosby (’ 96, p. 128) that the material borne along in or under the 
basal portion of the ice sheet while ascending the stoss slope is not 
carried down in its entirety along the lee slope, but becomes, on the 
contrary, to a large extent englacial. 
Another important feature in the distribution of drift, and conse¬ 
quently in that of the red boulders, which in all probability is to be 
referred, in part at least, to the influence of topography, is the occur¬ 
rence of areas of scant drift. Closely adjoining areas often present 
the most marked differences in this respect. The distribution of the 
drift, however, differs in no way from the normal, the long level 
peneplain remnants being deeply and uniformly covered, while the 
rugged and highly irregular areas are almost bare. 
Distribution in till. — In studying the occurrences of red bould¬ 
ers near the ledges from which they were derived, it became 
evident, that, while 75 per cent or more of the boulders represented 
in stone-walls were of this type, the amounts of fine material of 
this nature recognizable in the till were much less, being in some 
instances as low as 5 or 10 per cent. In this respect the Braintree 
train agrees closely with the Rhode Island train, the latter of 
which had at its outset not more than a tenth of its mass made up 
of fragments of the iron ore. In both cases the till shows a com¬ 
plete commingling of the local and foreign material even in the 
