Glacial History of New England Islands. — Upham. 87 
position, just as the plateaus of modified drift in southeasleni 
New Hampshire are explained (Geology of N. H., vol. iii, 
T878, pp. 155-164. 170-172). Where glacial drift mantles such 
deposits, as in the very massive Manomet hill, east of Ply- 
mouth, I regard the relationship and mode of origin as analog- 
ous with the Madison type of drumlins, having a nucleus of 
modified drift and surface of till (Am. Geologist, vol. xiv, pp. 
69-83, with maps and sections, Aug., 1894). The ample devel- 
opment of these series in southeastern New England seems 
referable, like the later plains in front of the moraines, to the 
large proportion of gravel and sand in the drift here borne 
forward by the ice-sheet. 
In the lower quarter or third of the thickness of the ice, it 
appears to have contained • drift eroded from the land over 
which the ice moved; and near the front under ablation at times 
of glacial recession this englacial drift became superglacial. 
Its sandy portion was m.ost readily washed away by rains and 
the water of melting, being deposited partly in great tunnels 
beneath the ice near its margin, partly in ice cafions and broad- 
er channels open to the sky, and also in large part beyond the 
ice border. The earliest glacial erosion, deriving gravel and 
sand from alluvium of the Tertiary stream courses, gave many 
pebbles that are waterworn and superficially decayed, which 
ha\ e plentiful representation in the Nashaquitsa series. The 
sand grains of these beds and of the Truro series are also often 
notably decayed. As all these deposits, up to the Truro beds 
which form the chief mass of the forearm of Cape Cod, have 
undergone deformations, of the same class as those of Gav 
Head but far less pronounced, it is apparent to my mind that 
glacial pressure was ef^cient to produce these disturbances both 
at an early stage of glaciation and at a late time near that of the 
Champlain depression and end of the Ice age. 
Till and Moraine Belts. 
Less till was carried to the extreme limit of the ice-sheet 
than might be expected. Revising his estimate of its average 
depth in the conspicuous moraine belt on the northwestern 
hills of Martha's Vineyard. Shaler thinks it no more than 40 
feet. In the extended region here considered, the till has less 
aggregate volume than the modified drift. Farther north. 
