Geology of Johnson County. 413. 
enclosed in limestone, which, in the State of New York, where the 
series is more complete, lies at a depth of more than five thousand 
feet below the coal measures.” 
The result of the most critical examination and study of the: 
phenomena as observed to-day, is such as to corroborate the state-. 
ment then made in regard to this subject, which is as follows :— 
“The coarse and fine sand were first transported, and, entering 
some fissure [probably a pothole] in the rock, continued in deposi- 
tion in this cavity, while a bed of similar sandstone was being 
formed outside upon the bottom of the sea. This ceased, and then 
came the clay, which continued in like manner, while the under 
clay of an exterior coal bed was in process of deposition. 
“ Lastly, the carboniferous mud, derived from the material of a 
coal seam, was filtered through the fissure, filling the remaining 
space, and spread out in the narrow seam beyond. There is no 
mingling of the material, as if resulting from the breaking up of 
a coal seam at a later and modern period. 
“Every part is as distinct as in the coal measures elsewhere ; 
and this only could have resulted from a participation in the cause 
then operating to produce those extensive beds of sand, shale, clay, 
and coal which make up the coal measures. This point is near the 
northeast margin of the coal basin, and beyond the limits of any 
productive coal seams; a few isolated patches of sandstone and 
shale being all the remaining evidence of the extension of the 
series in that vicinity.” 
It is believed that the immediate valley or channel of the Iowa 
River, from Coalville to Iowa City, and perhaps north from this 
point, in Johnson County, represents the channel of an old Deyo- 
nian stream, y 
Occupying a position in the east side of the valley of the Iowa 
River, where an abrupt curve is made, near Iowa City, is a patch 
of soft, friable carboniferous sandstone, having a length of one- 
fourth of a mile, and a breadth of one-eighth of a mile or less. 
This sandstone occupies a valley of erosion in the Devonian lime- 
stone, and which has a depth of between thirty and forty feet. 
That this was a valley of erosion, formed by the action of flowing 
water prior to the time when the sandstone was deposited, is- 
obvious, as the sides of this valley are seen, after the removal of 
the sandstone, to be smoothed and worn by the long-continued: 
action of running water. 
