410 Geology of Johnson County. 
bottom of ten inches, with unsymmetrical but smooth sides; upper 
margin smooth and somewhat flaring. 
- About half way from the top to the bottom, cavities have been 
formed in the sides by the action of the water which formed the 
pothole. The upper margin of this pothole has a small channel 
eut through to the east, apparently by the overflow. 
Pothole number two: This is one of the largest and most inter- 
esting examples to be found here. This pothole has been formed 
y the union of several minor ones. Its longest diameter is from 
east to west, somewhat subovate in marginal outline, sides unsym- 
metrical but smooth, more or less gently sloping to the bottom, 
upper margins unevenly rounded, depth seven feet, length from 
east to west seven feet, and width of the eastern portion at the top 
two and one-half feet, and marginal width of the western portion 
four and one-half feet, contracting at the bottom to a width of two 
and one-half feet. | 
In the west side of this pothole, about midway from top to 
bottom, large, more or less ramifying cavities, varying from three 
feet to eight feet in extent, have been worn by the action of the 
water which formed the pothole. The overflow to the east has cut 
a channel about three feet in depth and two feeet in width. About 
four feet to the right of the foregoing is a small bowl-shaped 
depression, with smooth symmetrical sides, and rounded or flaring 
margin. Near this is another smaller saucer-shaped depression, 
having a diameter of sixteen inches, and a depth of six inches- 
These are beautiful examples of how some of these potholes were 
begun. 
The following cut (from a photograph) will illustrate the form 
and position of “these depressions in relation to the large pothole 
above describe 
Pothole nëmbe three: Subcircular in outline, sides somewhat 
irregular, smooth, upper margin slightly flaring. For the first four 
feet the sides are nearly perpendicular ; below this point the hole- 
rapidly enlarges to the east, but soon contracts, and continues its 
downward course in the form of a gradually-narrowing oblique 
fissure, that finally unites with a rather large, more or less horizon- 
tal, crevice between the beds of rock.' 
1 This fissure is filled with a black, combustible, carbonaceous mud of 
bituminous matter, which is usually underlayed and sometimes over~ 
layed by a reddish-brown clay. 
