208 BRIGHAM—TOPOGRAPHY AND DEPOSITS OF MOHAWK VALLEY. 
were perhaps lacustrine, held up by the still persisting rock barrier at 
Aqueduct. 
Fluvial stage.-—North of the above gravel bed, midway, in a triangular 
recess between it and the cliffs, are some kame heaps rising 60 to 70 feet 
from the top of the gravel. Their sides are not abraded, and the lateral 
slope of the gravel plain toward their base also suggests that the river 
flood could not have risen, unless for short intervals, much above the 
present surface of the gravels. In a similar recess on the north side, 
west of the Nose and west of a creek entering from the north, are similar 
mounds, of which the highest rises to an estimated height of 80 feet. 
Their position ina kind of recess may have been a partial protection, 
but repeated observation confirms the impression that a swift and pow- 
erful current could not have left their slopes unharmed had it risen upon 
them for any length of time after lacustrine conditions ceased. 
MASSIVE LACUSTRINE CLAYS 
No reference, except by way of record, has thus far been made in this 
paper to a few deposits of massive clay, indicating long intervals of quiet 
deposition. Well records have not disclosed the presence of such de- 
posits in the valley to such a degree as had been anticipated from studies 
in the region to the southward. Such clays appear at Sylvan beach, 
Rome, Herkimer, and in some of the wells at Ilion and Frankfort. Of 
the wells disclosing thick masses of lacustrine clay, not one is midway 
of the valley, but all are either on the edge of the floodplain or beyond. 
The well at the Ilion Typewriter works was sunk 195 feet to rock with- 
out encountering clay. Hither, therefore, the clay was never a continu- 
ous deposit or it has suffered erosion. If the former, it was laid down 
in local, marginal lakes, but the thickness, especially at Herkimer, is not 
favorable to this supposition. The hypothesis of erosion is favored by 
the conditions at Ion. At the south edge of the floodplain is the well 
at the typewriter works. Within a mile and a half southward massive 
clays occupy almost all altitudes, from 70 feet below the river floodplain 
to 200 feet above it. It is also significant that at Herkimer 100 feet of 
clay are underlain by 30 feet of gravel, including a boulder 73 feet in 
diameter. At one of the Rome wells, also, 65 feet of clay and quicksand 
are underlain by 31 feet of hardpan. These facts look toward an 
early period of low altitude and slack drainage preceded by active gla- 
ciation and followed by erosion and giacial deposition. If an erosion of 
the clays took place in the Mohawk valley, it was in part glacial, as. is 
shown by the presence of the rock basin in the valley east of Utica. 
In an earlier paper the writer has reported a series of well records from 
