642 
mulations the sand would be thicker there 
than in the depressions, but the opposite was 
the case. The slight irregularities of the 
surface, therefore, are the result of original 
motor deposition and not of wind action. 
Observations upon other portions of the 
delta terrace revealed the same condition 
of things. In the gravel pit already re- 
ferred to, about three hundred yards to the 
north, the succession in the upper three or 
four feet exposed is substantially the same. 
The clayey bands are distinctly apparent, 
and the whole structure is conformable. 
In this pit there occurs, and was photo- 
graphed by us, a thick deposit of fine sand 
near the bottom, containing thin wavy 
bands of stratified clay, very similar to the 
upper one described in our main trench. 
Again, about a mile distant, toward the 
southeast, near the park, an excellent 
exposure of the terrace shows the same 
succession. With this, also, agrees the 
description given by Mr. Volk of his 
explorations on the same terrace in 1891, at 
a point about half way between the park 
and the present explorations. (See Pro- 
ceedings of the A. A. A. S., Vol. XLILI., 
1894.) In describing the strata, he says: 
“The soil in this place consists of nine 
inches of black or subsoil, tilled land, over- 
lying an undisturbed sandy loam composed 
of quartz sand, colored by iron and mixed 
with a yellow soil, the sediment of muddy 
water, the whole having a light yellow 
eolor. Three feet below the surface is a 
somewhat uneven stratum of red clay 
mixed with sand.” 
From all this it is clear that this deposit, 
up at any rate to the upper line of reddish 
clayey band, is part and parcel of the Tren- 
ton gravel. 
A most natural explanation of the depo- 
sition of these successive strata of sand 
and clayey bands is at hand in the closing 
floods of the glacial period which confessedly 
built up the terrace to within a few inches 
SCIENCE. 
[N. S. Vou. VI. No. 148. 
of several of the implements found in place. 
All the phenomena can easily be accounted 
for by the forces then known to be in opera- 
tion. The floods accompanying the close of 
that stage of the glacial period which 
formed the terminal moraine crossing the 
river at Belvidere brought down the débris 
from the melting ice until the delta terrace 
was built up to a height of about forty-seven 
feet. This, all readily admit. But it is 
easy to see that as the delta grew higher, 
and the material accessible to floods dimin- 
ished, the closing deposits would consist of 
finer material, the conditions being some- 
what like those of ordinary flood-plains, 
only in this case the forces were more ex- 
traordinarily variable and vast in their 
proportions. In the laststages of this epoch 
we may well suppose that during the 
months of July, August and September the 
waters running over this delta terrace were 
occasionally swollen enormously, though 
the elevation overflowed was such that any 
large masses of boulder-laden ice were 
prevented from sweeping over it, such as 
did during the earlier stages of the deposit. 
These floods would easily distribute large 
quantities of sand along the edge of the ter- 
race of the main stream, extending back for 
an indefinite distance or to the slightly 
higher deposits that had previously been 
made, and this under conditions so uniform 
that several inches might be accumulated 
without signs of bedding. On the subsi- 
dence of the floods the clayey strata would 
naturally accumulate, as shown in these de- 
posits. 
But how did the implements become in- 
corporated in the strata? By a process 
which is perfectly natural and credible. 
During the larger part of the year, when 
the melting of the glacial ice was proceed- 
ing at a slow rate, vast bars and abandoned 
channels of the main pebbly deposits of 
sand and gravel would be exposed, afford- 
ing to the aboriginal inhabitants a choice 
