This grand series of moraines stretches from the peninsula of Cape Cod
across the northern States, and passes in a north-westerly direction
into the British Possessions, over which it has been followed for some
400 miles. The disposition of the moraines, forming as they do a series
of great loops, shows that the ice-sheet terminated in a number of
lobes or gigantic tongue-like processes. Nothing seen by me suggested
any marine action; on the contrary, every appearance, as I have said,
betokened the morainic origin of the mounds; and Mr. Chamberlin assured
me that their peculiar distribution was everywhere suggestive of this
origin. No one who has traversed the regions I refer to is at all
likely to agree with Sir W. Dawson's view, that the American mounds,
etc., are the shore-accumulations of an ice-laden sea.
The morainic origin of these accumulations having been demonstrated
by American geologists, we are now able to draw another parallel
between the European and American glacial deposits. We have seen that
in Europe the ice-sheet of the latest glacial epoch was by no means
so extensive as that of the preceding glacial epoch. The same was
the case in North America. Moreover, in America, just as in Europe,
the latest occupant of the land was not the sea, but glacier-ice.
In Scotland and Scandinavia the gradual disappearance of the latest
ice-sheets was marked by a partial submergence, which in the former
country did not greatly exceed 100 feet, and in the latter 700 feet.
In America, in like manner, we find traces of a similar partial
submergence. In Connecticut this did not exceed 40 or 50 feet, but
increased to some 500 feet in the St. Lawrence, and to over 1000 feet
in the Arctic regions. If there ever was during the Glacial period a
greater submergence than this in North America it must have taken place
in earlier glacial or interglacial times, but of such a submergence
no trace has yet been recognised. In this respect the American record
differs somewhat from our own, for in Britain we have evidence of a
submergence of over 1000 feet, which supervened in times immediately
preceding the latest great extension of continental ice.[P] But nowhere
in middle Europe, and nowhere in North America, in the region south
and west of the great lakes, is there any trace of a general marine
submergence. The "Palæocrystic Sea" is as idle a dream for the northern
States of America as it is for any part of Europe.
[P] See footnote, p. 173.
VI.
_The Results of Fluvio-glacial Action in North America._
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