S2 Some Geological Prohlemii — Calvin. 
of twenty feet. The concjlomerate bed, number 6 on Robin- 
son's creek, is here well marked, the fragmentary materials being 
interstratified with irregularly contorted beds of shale and sand- 
stone disposed at all imaginable angles and frequently thinning 
out within a few feet. At one point observed in the face of the 
bluff the conglomerate bed had a thickness of eight or ten feet, 
while only a short distance to the left the same layer had thin- 
ned to eight or ten inches. In the face of the bluffs at a 
height of about fifteen feet, occurs a layer of impure coal ahout 
ten inches in thickness, and above the coal are regular, horizon- 
tal, even-bedded layers of sandstones representing number 8 on 
Robinson's creek. Below the coal seam all the strata are con- 
fused, contorted, irregular; above the coal seam the layers are 
even, regular and horizontal. 
There are two distinct sandstones belonging to different ages, 
in the region about Pine creek and Montpelier in Muscatine 
county, Iowa. One belongs to the Middle Devonian, the other 
to the Lower Carboniferous. To avoid confusion I have used 
at different times iii this article the term Spir Jer-hearing 
sandstone to denote the earlier of the two. We may speak of 
them hereafter respectively as Devonian and Carboniferous 
sandstones. 
The Carboniferous sandstone is extensively developed through- 
out the region from Buffalo to Muscatine. An exposure of 
nearly a hundred feet in thickness may be seen at Wild Cat 
den, a mile and a half above Pine Creek mills. At Wyoming 
Hill, a short distance below Fairport, it is well exposed and 
furnished numerous remains of Coal-Measure plants. In the 
lower part of the city of Muscatine it is again seen in the high 
bluff, lying as usual above a layer of rather impure coal. At 
.one locality on Pine creek, above Wild Cat den, this sandstone 
is somewhat more indurated than usual, and is quarried to sup- 
ply the local demand for building stone. 
The coal seam which appears everywhere to accompany the 
Carboniferous shales and sandstones of the region, varies in 
thickness from eight or ten inches to two or three feet. For 
the most part the coal is of inferior quality, being more or less 
shaly, and containing large quantities of pyrites of iron. At a 
few localities, however, notably near Buffalo, the coal has been 
profitably worked. 
