978 
The gravel plain to the east and north of 
the point where the finds are made ends 
abruptly at the margin of the post-glacial 
valley, in a bluff about forty feet in height, 
with a slope which is about as steep as the 
material of which it is composed will lie. 
The relations shown on the New Jersey 
side of the river are in a general way du- 
plicated on the Pennsylvania side. The 
gravel of glacial age has a similar dis- 
position, but the border of the valley on 
that side is not so sharply defined, indica- 
ting that the more recent cutting of the 
stream has been on the east. The steepness 
of the bluff of gravel at the points con- 
cerned is in itself proof of the recency of 
the excavation on this side. 
The surface of the plain is slightly un- 
dulatory, though the relief is usually but 
a few feet. In places erosion has affected 
it to some slight extent, and in places its 
surface appears to have been left slightly 
uneven by the deposition of the material of 
which itis made. Its surface is also char- 
acterized at various points by low mounds 
and ridges of sand heaped up by the wind. 
By this means an element of undulatori- 
ness has been added to the surface as origi- 
nally left by the deposition of the main body 
of sand and gravel involved. 
While the plain consists of sand and 
gravel, so far as its general constitution is 
concerned, its surface is in many places 
coated with a thin layer of sandy loam, 
which contains occasional pebbles similar 
to those which make up the body of the 
gravel beneath. It is not always possible 
to say to what extent the surface loam rep- 
resents the last stage of deposition of the 
glacial sands and gravel ; to what extent it 
represents the surface accumulation of 
loamy matter brought up from lower levels 
by the action of biotic agencies, such as 
worms, ants, burrowing mammals, ete. ; or 
to what extent it represents deposition by 
marine or estuarine waters which stood 
SCIENCE. 
[N. S. Von. VI. No. 157. 
over the region after the glacial drainage 
ceased to flow through this part of the Dela- 
ware. 
Relations similar to those where the 
human relics just south of Trenton are 
found characterize the east side of the Dela- 
ware for many miles further south. In this 
direction materials derived from glacial 
waters are less readily identified at most 
points, but the topography and relations of © 
the plain bordering the Delaware are such 
as to show that it was developed contem- 
poraneously with the plain at Trenton. 
Even where not made up chiefly of glacial 
materials, the plain further south, like that 
at Trenton, is slightly undulatory, and is 
coated, in places, with dune sand. Such 
sand is especially likely to be found on the 
west edge of that part of the plain which 
lies east of the Delaware, and just east of 
the line where the plain descends with a 
‘bluff face to the flood-plain of the stream. 
Well-marked dunes sometimes appear in 
this situation, and dune sand in larger or 
smaller quantity is so general that its pres- 
ence along the edge of the plain above the 
valley may be said to be the rule, rather 
than the exception, between Trenton and 
Camden. 
The same is true of the tributaries which 
come down to the Delaware from the east. 
Although they did not bring down glacial 
sands and gravels, they brought down sands 
and gravels of other sorts, partially filling 
their valleys, which, like the Delaware, have 
been re-excavated since. On the bluffs of 
the tributary valleys, as well as along the 
main stream, dune sand is of frequent 
occurrence. In the dune sand along these 
tributaries, relics of early peoples, consist- 
ing of chips of argillite, arrow-heads, and 
half-fashioned tools of various sorts, are 
frequently found. 
Sand is found in similar relations at some 
points on the Delaware above Trenton. At 
many points it has been blown up from the 
