159 
Plate CXXII represents the lowest one, the bottom of which 
is about twenty-eight feet above the river. The side facing the 
river was eroded or has fallen away, leaving the interior exposed 
from top to bottom. Its place of beginning is somewhat ob- 
scurely defined, but may be recognized by tracing the concavity 
upward to the top of the rock wall. Originally it must have been 
approximately twelve feet in depth, by four or five feet in width 
down to where it begins to taper to the bottom. The two-foot 
rule, standing at the righthand side of the hole, will serve for a 
scale of measurements 
Plate CX XIII represents the other one in the hemlock grove, 
located at a higher level than, and to the south of the one first 
described. The upper part only is exposed, to a maximum depth 
of about five feet. It is irregularly elliptical in cross section, 
approximating six by seven and a half feet, with the longer axis 
extending toward the river. The rim and sides are well rounded, 
and erosion of the exposed side fronting the river is plainly ap- 
parent. The depth is unknown, as it is filled to the level of the 
forest floor with rock and vegetable debris, on top of which is a 
large boulder and in which is rooted a living tree about four feet 
in circumferen 
Plate C. xIV represents the one on the border of the herba- 
ceous grounds. It is the smallest of the three, but is the best 
preserved. It measures approximately two feet in depth by 
wo feet in width, with a small bowl-like depression just above 
he upper rim, which was probably the original beginning of the 
hole, before the eroding contents found final lodgment at the 
lower level. 
If the facts in connection with these pot holes are analyzed 
and interpreted, they indicate in unmistakable terms the follow- 
ing sequence of events.—The stream which in Pre-Glacial times 
occupied the valley of the Bronx and flowed though the depres- 
sion where the tracks of the Harlem branch of the New York 
Central & Hudson River Railroad are now located, was ob- 
structed by ice or glacial debris and diverted to the eastward, 
where it found two outlets,—one through the narrow swale 
in which the morphological and herbaceous plantations are 
