145 
rock in Medford, on the extreme northern margin of the Boston 
Basin, or at least to the probable eastward extension of those 
beds beneath the drift; although the strong easterly trend of 
the glacial movement in the harbor allows us to regard the 
prominent conglomerate ledges in the central part of the basin 
as a possible source of some of the conglomerate erraties in the 
Nantasket Peninsula and Cohasset. In the Nantasket drumlins, 
granitic rocks, felsites, quartzite, etc., from the high land 
north of the Boston Basin, form a small but very obvious or 
noticeable fraction of the till, and in some cases exhibit lith- 
ological peculiarities enabling us to refer them to the parent 
ledges, as in the case of the bright red felsite from Saugus 
Centre. А portion of what might be mistaken for conglom- 
erate is brecciated felsite, and another portion is brecciated or 
pebbly slate. Over the granitic area of Cohasset and Scituate, 
as a matter of course, the crystalline rocks predominate in the 
till, and the slate, which does not bear glacial transportation 
well, is subordinate, except, perhaps, in the finest part of the 
H 
till. There is, however, among the larger masses or fragments 
in the till, a quite liberal sprinkling of both melaphyr and con- 
glomerate from the Nantasket ledges. These are especially 
noticeable along the shore, the number and average size, with 
oecasional exceptions, diminishing rapidly as the distance 
increases. 
The surface distribution of the larger bowlders indicates that 
they are not equally abundant in all parts of the till; for 
while the majority of the drumlins are remarkably smooth, pre- 
senting on the surface but few bowlders larger than those to be 
seen in the stone walls, others, like Booth Hill in Scituate, are, 
at least on certain slopes, thickly strewn with masses from 
three to eight feet or more in diameter. The bowlders are, in 
some cases at least, clearly most abundant along those lines 
where the till has been eroded by standing or running water and 
which may thus be regarded as in some sense ancient shores or 
OCCAS PAPERS B. 8. N. Н. IV. 10. 
