584 Surface Geology of Eastern Massachusetts. [ October, 
It appears probable that but few of those surface unevenesses 
which are impressed upon the rocks have had a glacial origin, 
At any rate, a large number, including all the more important, 
of these rock-impressed inequalities of the surface in this region 
are doubtless much older than the glacial epoch which has but 
recently passed away, and, if due to glaciation at all, were sculpt- 
ured during some earlier reign of ice. Such large rivers as the 
Merrimac, Nashua, and Blackstone are unquestionably of pre- 
glacial origin. Their courses are parallel with the strikes of the 
rocks over which they flow; and the first two, at least, occupy 
well-marked geological valleys. Furthermore, it is hardly con- 
ceivable that glaciation can have been the cause of rock-bordered 
valleys transverse to its line of action, as is the Merrimac in 
Massachusetts ; and the valley of this stream, so far from being 
the product of glaciation, probably exists in spite of the tendency 
of the ice-cap to obliterate it. 
The question, also, as to what extent the so-called fiords of 
this region are due to the excavatory power of ice during the 
last glacial period can hardly be regarded as settled. Reference 
is made, of course, only to fiords carved from the solid rock, 
which is not the case with those in Barnstable County. The 
fact that these inlets are chiefly found on coasts transverse to 
the direction of glacial movement becomes, I think, less an ob- 
stacle to the denial of their glacial origin, when we reflect that 
the tendency of an ice-cap would be to fill up and obliterate 
‘such coastal inequalities as were transverse to its line of progress, 
and at the same time to clean out such as coincided with its 
march. If the superficial deposits were removed from the New 
Hampshire coast, the northeastern part of Essex County, and 
Eastern Plymouth County, it is not improbable that these north 
and south shores would present irregularities nearly as marked 
as those that indent our southern coast. 
It is a significant fact that the northern shore of Massachu- 
setts Bay, though parallel with the northern shore of Buzzard’s 
Bay, and hence similarly related to the course of glacial action, 
is destitute of conspicuous indentations that can be regarded a8 
the work of the ice-sheet ; for all the important rock-bordered 
deflections of this coast-line have their major axes tance 
the line of march of the glacier. Marblehead harbor 1s one © 
these northeast and southwest troughs; and here we have eV! 
dence of a unique and conclusive character, proving aes 
question its preglacial origin. This strait — for such it would | 
