772 G. K. GILBERT 
to the attack of the waves is twelve to fifteen feet high and free 
from talus, and the section is fully exposed fora half mile to 
the east. The lower part of the bluff is composed of till, eight 
to ten feet being visible, and the base not seen. Above this is 
laminated clay, a deposit spread by the waters of the glacial 
lake Iroquois. 
To casual observation the till appears to be a single continu- 
ous body, but more careful examination shows that there are two 
parts separated by a horizontal line between five and six feet 
above the surface of the water. Both tills are reddish-brown, 
but there is a slight difference in color, the upper inclining 
toward orange and the lower toward purple. At various points 
a bitter efflorescence was seen on the surface of the upper till, 
and this was not observed on the lower. Both tills are moder- 
ately supplied with pebbles and bowlders, the material of the 
larger fragments being chiefly sandstone and limestone of the 
subjacent Medina and contiguous Hudson River formations, and 
ranging in diameter up to about twenty inches. There are also 
crystalline erratics from a distance, and a few of these are sev- 
eral feet in diameter. Such larger bowlders were not seen in 
situ in the bluff, but occur here and there on the beach and in 
shallow water near the shore, where they have evidently been 
left by the erosion of the enclosing till. 
Just at the top of the lower till bowlders are comparatively 
abundant, and such as are flat lie with their greater dimensions 
horizontal. Their upper surfaces form parts of a level line 
drawn across the bluff (Plate XIV), and it was their alignment 
which drew attention to the compound character of the till. So 
far as the upper till betrays structure, its lamination is approxi- 
mately horizontal. Much of the lower till is somewhat definitely 
laminated, and the lamination is contorted. In some places 
there are irregular masses of gray till mingled with the red, the 
general arrangement being suggestive of structures commonly 
seen in the Archean complex. i 
Examination showed nearly all the bowlders at the plane of 
separation to be striated on their upper surfaces. The directions 
