254 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
In working out the boundaries of the train, a distinction was 
made between boulders and pebbles found in the deposits of modi¬ 
fied drift and those found in the till. The boundaries were based 
wholly on observations of the latter. An examination of the strati¬ 
fied deposits along the northward sloping valleys disclosed the fact 
that, contrary to what might be expected, red pebbles outside the 
boundary determined by observations on the till were exceptional, 
and only found after careful search, and even then only at slight 
distances beyond the normal boundary. The indications point 
strongly to a drainage reversed by the ice, the deposits being, in 
all probability, laid down during the higher stages of Glacial Lake 
Bouve (Crosby and Grabau, ’96, p. 128) when the confined waters 
still found outlet to the southward through the valley now occupied 
by Weymouth Great Pond, and also that lying between Holbrook 
and Randolph (Monatiquat Bay of Glacial Lake Bouve). Red 
pebbles were also sparingly found in certain coarse and irregularly 
stratified deposits, probably of subglacial origin, lying in northward 
sloping valleys outside the normal boundary. Such occurrences 
are doubtless due largely to the tendency which subglacial streams 
must possess, especially after the movement of the ice has ceased, 
to follow the natural slope of the land even when it is directly 
opposed to the gradient of the ice when in motion. 
The occurrence of pebbles or boulders of red sandstone outside 
the normal boundary in other than the modified drift just mentioned 
has been noticed at only one point, namely, in the till elevation near 
the northern end of Great Pond of Braintree. Here, quite a number 
of boulders with a more or less prominent tinge of red were noticed, 
but were clearly, in the majority of cases, simply arenaceous bands 
in the conglomerate. In other cases, the resemblance to the red 
outcrops was more perfect, leaving the origin in some doubt. If 
derived from the latter outcrops, they would indicate a movement 
considerably more easterly than the average. If such was the case, 
the movement was evidently spasmodic and of short duration, prob¬ 
ably marking the last movement before the ice became stagnant. 
No traces of such boulders in the continuance of the line of motion 
indicated were observed. 
Comparison with other trains of New England. — The average 
easting of the Carboniferous boulder train just described agrees 
closely with the train of red felsite observed by Prof. W. O. Crosby 
(’94, p. 272) in Ilingham, the former having an easting of 60° and 
