146 KANSAS ACADEMY OF SCIENCE. 
In many places in the heavier ledges the concretionary structures assume 
gigantic proportions. They are often twisted and crumpled into grotesque and 
fantastic shapes. These forms are so radically different from anything else in 
the region that to the common mind they suggest volcanic action, and the geolo- 
gist is often wearied with explaining to the farmers along the line of outcrops 
that neither volcanoes nor earthquakes had anything to do with these peculiar 
forms. Some of these concretions are as much as ten feet in diameter, and con- 
sist of a series of dome-shaped layers from one to two inches thick, arranged one 
within the other. These layers are often in direct contact; or again they may 
be separated by several inches. Not infrequently the inner layers have disap- 
peared by concentric decomposition, and only the outer shell remains, often 
forming a cave in which a man may stand upright. 
These masses of clay ironstone are often found in the form of streaks or 
bands throughout the sandstone, usually following the line of stratification. 
The box-shaped and spherical concretions described above are ordinarily found 
in the clay banks, but sometimes occur in the sandstone. Doctor Hayden evi- 
dently referred to these concretionary bands when he said: ‘‘There are also 
some seams of iron ore, which, when broken with a hammer, gave forth a sound 
much like that from old pot metal. It is really a pretty fair iron ore, but quite 
silicious and impure.’’ 
The theory of the origin of concretionary structure seems at the present time 
to be rather indefinite. This article makes no attempt at an explanation of these 
most interesting phenomena. It is a question that calls for persistent and sys- 
tematic research; and it is to be hoped that some competent investigator may 
shortly give it his attention. When this shall be done the Dakota group will 
supply an abundance of material. 
Throughout the Dakota area there are numerous peculiar forms of erosion. 
Castles, chimneys, towers and forts are some of the popular names with which 
these marked forms are designated. Pulpit rocks, near Carneiro, and Rock City, 
southwest of Minneapolis, Kan., are perhaps, the most striking forms. The 
pulpit rocks are on Alum creek, a hile south of Carneiro, Ellsworth county, Kan- 
sas. At this place a ledge of rather hard gray sandstone rests on a much softer 
ledge. Along the side of the hill the softer ledge naturally weathers away more 
rapidly. The upper and harder layer is in most places entirely removed, but ina 
few cases it persists in the form of large, irregular, spheroid masses, bearing not a 
little resemblance in shape to the large puffball of the prairies. Some of these 
rock masses are twenty feet in diameter and fifteen feet high. They are usually 
found lying flat on the ground, but are sometimes tilted or even on edge. Ina 
few cases there is left a pedestal of the underlying soft sandstone, supporting a 
mass of rock many times its own size. In such case the similarity to a puffball is 
still more strongly marked. One might almost imagine that the fungus, stalk 
and all, had simply increased in size until it had reached its present gigantic 
proportions, and had then been petrified. The largest of these pulpit rocks has 
a pedestal twelve feet high and not more than six feet across at the top, on which 
is supported a globular mass of sandstone fifteen feet high and twenty feet in 
diameter. (See plates IX, X.) The marked stratification of the upper layer 
gives to the rounded mass a peculiar appearance, not unlike that of jelly-cake. 
This harder ledge may be seen outcropping on a number of hills in the vicinity ; 
but in no other locality are the marked forms of erosion so conspicuous as at the 
spot just described. 
Rock City, five miles from Minneapolis, Kan., consists of several hundred 
rock masses very like those at Carneiro, except that here the pedestals are 
