( 80 ) 
and the old channel are below the 60-feet contour just 
south of Williamsbridge. ‘The terrace of cobblestones is 
well shown at this point by the projecting 60-feet contour, 
just under the number 60. The location of the upper part of 
the old channel where the little brook comes into the Bronx 
is also shown, and the present almost unrecognizable divide 
may be identified between it and the brook that flows south 
into the East River along the old channel. This latter brook 
is now practically obliterated by street improvements. It 
cuts the 4o-feet contour about a mile and a half south of 
Williamsbridge, and the 20-feet contour three miles south of 
the same point. The Bronx, however, passing into the gorge, 
crosses the 4o-feet contour a quarter of a mile from the entrance 
and the 20-feet contour at West Farms. The new route to 
salt water is shorter than the old by some two miles, being 
three as against five, and therefore the fall of 50 feet is the 
more accentuated under present conditions. 
The gorge is somewhat open at its upper end, but it soon 
closes in and has steep and jagged walls. Some 65 to 75 
feet from the bridge at its entrance, and on the west bank, is 
one of the two potholes, which were described by Dr. N. L. 
Britton in the Transactions of the New York Academy, Vol. 
., p. 181, 1881. It is broken down on the outer side, as is 
usual with potholes below which the creating stream has cut. 
The inner half remains, however, and is about 12 feet deep. 
The bottom of the bowl is quite perfect and shows that the 
hole must have been 5 or 6 feet in diameter. The bottom is, 
by aneroid, about 25 feet above the river surface. The walls 
are still smooth and scarcely decayed at all. A few paces 
up the hillside to the southeast is another, that is even more 
impressive. ‘This is only about 5 or 6 feet deep, but much 
more of it remains than of the lower one. It is 6 feet 2 inches 
in diameter, and contains a large rounded bowlder, 4 feet by 3 
feet by 2 feet 6 inches. A treea foot in diameter sprouts out 
from beneath the bowlder. This pothole is 30 feet above the 
lower one and therefore over 50 feet above the river. Back 
of it, the hill rises at its summit some 20 feet higher. About 
