1878.I Glacial Drift in North America. 61 
Ridge. Some of the stones found near Richmond must 
have been brought 80 miles if they travelled in a direCt line 
from the parent rock. At Richmond this deposit is said to 
present itself at various heights from the river-bank to the 
tops of the hills, mantling the irregularly denuded surface 
of the underlying formations, resting at one place on the 
Upper Miocene, at others on the Eocene, or yet older 
deposits.* 
At Trenton this deposit is principally composed of crys- 
talline rocks, many of distant origin, but none I believe 
have been noticed that may not have been derived from 
formations existing within the drainage area of the Dela- 
ware and its territories. Trenton is often mentioned as 
being about the southern limit to which the northern ice 
reached in the valley of the Delaware in glacial times, but 
I could find no traces of glaciation in the neighbourhood ; 
and Prof. Cook informed me that it has not been noticed 
farther south in the valley than near Belvidere, about 
50 miles in a direCt line N.N.W. from Trenton. Prof. Cook 
and Prof. Smock have now traced the southern boundary of 
the land ice pretty clearly across the State of New Jersey, 
from the neighbouroood of Amboy, on the Atlantic coast, to 
Belvidere, on the Delaware. From thence it runs across to 
near Harrisburg, in the valley of the Susquehanna, where 
Prof. J. P. Lesley informed me were the most southern 
glaciated rock surfaces in that valley. North of an undu- 
lating line passing through these points the surfaces of the 
bed-rocks are rounded and polished, and scored with glacial 
striae. By means of these markings, and by the direction 
from which transported rocks have been brought from their 
parent beds, the course of the ice has been mapped out 
from the Canadian boundary, where it was so thick as to be 
able to over-ride and move independently of the valleys, up 
to its southern termination, where it is found conforming 
with the direction of the main drainage channels. South of 
the line to which the northern ice extended the rock surfaces 
are often decomposed to a great depth. This is especially 
evident where the bed-rock is gneiss or granite. In such 
cases, for more than 50 feet from the surface, the rocks have 
often been changed to a clay that may be dug with a spade ; 
whilst that it has not been otherwise reconstructed is evi- 
denced by the faCt that veins of quartz running through it 
remain in their original position.! Over the glaciated 
* Ibid., p. 106. 
f See T. Sterry Hunt, “ Decomposition of Crystalline Rocks.' Amer. 
Journ. Sci., 1874, vol. vii., p. 60. 
