88 The Ameticaii Geologist. Angust, i899 
throughout New England in general, I believe that their ratio 
must be about two or three to one; and in the more thickly 
drift-covered Northwestern States, it appears to be, on an aver- 
age, ten or fifteen to one. Nowhere, however, was till carried 
in great volume to the boundary of glaciation. It seems to 
have been borne forward as material scattered through the 
slowly flowing lower part of the ice-sheet, mostly transported 
onlv a few miles, but including, especially in the marginal 
moraines, many boulders carried higher into the ice than the 
chief part of the drift. The middle and upper parts of the ice- 
sheet moved much faster than its friction-hindered and drift- 
laden lower portion; hence marginal moraines have usually 
more boulders, and more drift derived from great distances, 
than the general sheet of till. 
Professor Shaler argues that the moraine belts of the New 
England islands and Cape Cod, occurring mainly on high 
tracts, were formed by an attenuated border of the ice-sheet, 
here so thin that it floated on the sea over valleys, while yet re- 
maining as a united mass, and beyond was grounded upon the 
ridges, depositing the morainic drift. Westward, however, we 
cannot doubt that the same marginal drift continues on the sea 
bed between Martha's Vineyard and Block island, and thence 
to Long Island. The belts sweep in similar lobate and con- 
centrically curving course as in the interior of the country. 
Therefore I think, after noting the courses of the two chief 
belts, the outermost on Martha's Vineyard and Nantucket, and 
the second on the Elizabeth islands and Cape Cod, that the ice- 
sheet at the times of their formation reached far onward to the 
east, on the adjoining shoals and the more distant George's 
fishing bank. As before stated, the sea, according to my op- 
inion, then covered less of the continental border in this lati- 
tude than now, the shoals and fishing bank having been very 
probably land areas when the ice finally retreated. 
Duration of the Quaternary Era. 
From the supposed deposition and ensuing erosion of very 
extensive sand deposits upon a great area of southeastern Mas- 
sachusetts, since the Tertiary era, Shaler estimates the Quater- 
nary era to have comprised not less than a million years. The 
escarpment boundaries of portions of these sand deposits. 
