66 Discovery of Stone Implements in [January, 
any rock older than the Potsdam sandstone in the deposits 
below the clay ; while in a period subsequent to the depo- 
sition of the clays and sands, boulders of granite are by no 
means rare.* 
In the southern part of the State of New York and in 
New jersey they are not uncommon. At Marion, at the 
section of the till to which I have already referred, the top 
bed is a light-coloured sandy clay, similar to that at Trenton. 
Lying on and sometimes imbedded in this are large 
boulders, scattered over the surface. The sandy clay rests 
diredtly on the till, and is about 3 feet thick. Both here and 
at Trenton these great boulders were much larger than any 
I saw in the underlying till or drift. At Trenton they are 
often seen in the formation of new streets on the outskirts 
of the town. Some of them are 7 or 8 feet across, and most 
require blasting before they can be removed. I learnt from 
Prof. Smock that these blocks are distributed over much of 
the State, and he spoke of particular boulders occurring at 
a considerable altitude. I do not know, however, how high 
they occur, but probably this interesting question will be 
worked out by the Geological Survey of New Jersey, as well 
as the distances which they must have travelled from their 
parent rocks. 
Nor does the Delaware form the southern limit of the 
far-transported boulders. They appear to bear the same 
relation to the drift-beds in Virginia, for Mr. Wallace, in 
his account of the discovery of stone-implements near 
Richmond, speaks of boulders in the surface-soil, and of 
large blocks (8 feet by 12) resting on the gravel. 
It is obvious, as Prof. Hall and Dr. Newberry have 
pointed out, that these great blocks of stone must have 
been carried to their present position by floating ice. Any 
flood of water sufficient to move them would certainly wash 
away the sandy loam in and on which they rest, and such a 
mode of transport would not account for their position scat- 
tered here and there over the great undulating plain that 
extends from Trenton to the sea ; nor could they have been 
left by the great ice-sheet, as they are found far beyond the 
limits to which it reached. Sometimes we hear the distri- 
bution of the upper glacial beds ascribed to a second Glacial 
period, when the ice again covered the land. But ice could 
not have moved thus for hundreds of miles over beds of 
gravel and sand without disarranging them, and nowhere in 
America has any sign been noticed of a second advance of 
* Geology of New York, Part IV., p. 319. 
