308 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
tliat the juxtaposition of the two, as seen to-day, must have been 
produced in some such way as this. 
In a large number of areas examined on the north side of Pasture hill 
under conditions particularly favorable for such an examination, on ac¬ 
count of the extensive quarrying and building now going on, nowhere 
has a glaciated area preserving the striae on distinctly disintegrated 
materials been found, although it is quite possible that they do exist. 
Many of the undecomposed and glaciated rocks show joint fractures, 
so that if we accept the post-glacial disintegration hypothesis we have 
to ’suppose that disintegration has taken place in one locality to a 
depth of “even fifty feet” and in another immediately adjacent 
locality not at all, there being no evidence that the rocks, which evi¬ 
dently are of uniform texture, are not of uniform composition. 
When the ice passed over the dike and dragged portions of the 
partially disintegrated diabase with it in its onward course, it would 
naturally take up material of all kinds. Some of the boulders would 
be of quite fresh rock, others already well decayed. When these 
boulders were deposited by the subsequent melting of the ice they 
would be exposed to disintegrating agencies similar to those acting 
on the diabase outcrop. Reference has been made to boulders on 
the summit of Pine hill and in the sandy soils of the Mystic river 
valley to the eastward of the dike. Of the four largest on Pine hill 
none are disintegrated; two, however, which are quite angular, and 
close to the parent dike, show, at least externally, signs of decompo¬ 
sition and disintegration; the other two are well rounded and still 
quite hard, so much so, that it was with considerable difficulty that 
a specimen could be broken off. Of those buried in the soils of the 
basin, on the authority of Mr. Barnes and others who have seen 
them, it may be stated that except for a zone of two inches or less in 
depth, the rock is in appearance no more altered than is the fresh 
