1896.] NEW YORK ACADEMY OF SCIENCES. 21 



the old channel are below the sixty feet contour just south of 

 Williams Bridge. The terrace of cobblestones is well shown at 

 this point by the projecting 60 ft. contour, just under the 

 number 60. The location of the upper part of the old channel 

 where the little tributar^^ brook comes into the Bronx is also 

 shown, and the present almost unrecognizable divide maj^ be 

 identified between it and the brook that flows south into the 

 East River along the old channel. This latter brook is now 

 practically extinguished by street improvements. It cuts the 40 

 ft. contour about a mile and a half south of Williams Bridge 

 and the 20 ft. one, three miles south of the same point. The 

 Bronx, however, passing into the gorge, crosses the 40 ft. con- 

 tour a quarter of a mile from the entrance and the 20 ft. one 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 ft. is the more accentuated under present condi- 

 tions. 



The gorge is somewhat open at its upper end, but it soon 

 ■closes in and has steep and jagged walls. Some 65 to 75 ft. 

 from the bridge at its entrance, and on the weat bank, is one of 

 the two potholes, which were described by Dr. N. L. Britton in 

 the Transactions of the New York Academy Yol. I. 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 re- 

 mains, however, and is about 12 ft. deep. The bottom or bowl 

 is quite perfect and shows that the hole must have been five or 

 six feet in diameter. The bottom is by aneroid, about 25 ft. 

 about 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 ft. deep, but much more of it remains than of the lower one. 

 It is 6 ft. 2 in. in diameter, and contains a large rounded 

 bowlder, 4' x 3' x 2', 6". A tree a foot in diameter sprouts out 

 from beneath the bowlder. This pothole is 30 ft. above the 

 lower one and therefore over 50 ft. above the river. Back of it, 

 the hill rises at its summit some 20 ft. higher. About a half 

 mile east of south from these potholes is another smaller but 

 very perfect one, on the eastern edge of a rocky ledge and on 

 the 100 ft. contour. It is a foot or less in diameter and about 

 2 ft. deep. All three of these potholes are shown on the map 

 by round dots. The last named one indicates that rapid and 

 extensive currents must have flowed for a time even over the 

 high ground. 



The fresh condition of these potholes seems to indicate that 

 the lapse of time since they were formed has not been geolog- 



