168 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
permanently trom the Basin, and the land had subsided, and continued 
to subside until several hundreds of feet of clay had been deposited. 
The direction of movement of the glacier which produced the tillite 
is most important. There are a number of considerations which in- 
dicate a direction from the southeast to the northwest. Though not 
certainly due to ice thrust, the plication of the intercalated bed men- 
tioned above, points to such a direction of movement. Again in 
the description of this locality (page 155) it should be noticed that the 
beds intercalated in the tillite strike at an angle of from eight to ten 
degrees more east than the main body of the slate higher up. This 
must mean either a diastrophic change in the attitude of the beds, or 
that the intercalated beds sloped downwards towards the level of the 
water in which the slate was deposited. There is no evidence of an 
eroded zone between the transition-beds and the slate, so it does not 
appear that there is any unconformity. The beds in question slope 
from the east towards the west. According to Prof. James Geikie 
(1895, p. 24), beds intercalated in till are diagonal and not as a rule 
horizontal, and slope towards the ice-front. It would appear that the 
beds in the tillite at Squantum Southeast dipped westward, and if this 
was the case, and the difference in strike is not due to diastrophic move- 
ment, there would seem to be good reason for believing that the ice 
came from an easterly direction. Then again, a consideration of the 
slate fragments might also indicate an east-west direction of ice move- 
ment. In the tillite at Hyde Park, Milton Upper Mills, Roslindale, 
I have not observed slate fragments. At Squantum, and Atlantic 
the rock fragments in the tillite show a majority of pink granite, with 
melaphyre and quartzite coming next in abundance. If the ice had 
come from the north, the granite fragments could be explained, but 
not the melaphyre. If it had come from the west, the melaphyre 
fragments could be explained, but no pink granite of the variety found 
in the tillite is known in that direction. If the ice came from the south 
the pink granite could be accounted for, but not the melaphyre. If 
the ice came from the southeast, however, both the pink granite and 
the melaphyre are explained, for at Nantasket, Cohasset, and Hing- 
ham these rocks are found in situ. The fact that the largest 
boulders found in the tillite are of pink granite and melaphyre, and 
that these are found together, suggests a place of origin for both near 
the same locality. I have not forgotten that Pleistocene drift may 
hide some outcrops, and that the above suggestion cannot be proved, 
but so far as known outcrops go, it is a legitimate speculation, and when 
joined to the other evidence of the direction of ice movement appears 
