IOWA ACADEMY OP SCIENCES. 
57 
individual layers in their oblique course from top to bottom of 
the exposure. The facts confirm the statement that the beds 
were deposited one by one in the position in which we now find 
them. 
On the west side of the Mississippi, south of Le Claire, the 
usual oblique bedding is seen in the bank of the river, below 
the level of the plain on which the lower part of the town is 
built. The individual beds, as in ail the characteristic expos- 
ures of this formation, range from eight to twelve inches in 
thickness. Above the level of the beds exposed in the river 
bank there is another series of Le Claire beds that depart some- 
what from the ordinary type. Near the base of this second 
series the layers are thick and the rock is a light gray, porous, 
soft, non- crystalline dolomite. These grade up into thinner 
and more compact beds, but the lithologica.1 characters are 
never quite the same as those of the more typical beds at a 
lower level. The soft, porous gray-colored beds contain casts 
of Dinobolus conroM (Hall). The same species ranges up into 
the harder beds, but the characteristic fossils above the soft, 
porous layers are casts of small individuals of Atrypa reticularis 
and a small, smooth- surfaced Spirifer. The layers become 
quite thin in the upper part of the Le Claire. They show many 
anomalies of dip, but, so far as observed, they do not as a rule 
stand at as high angles as do the harder and more perfectly 
crystalline beds of the lower series. The existence, however, 
of tumultuous seas is no less clearly indicated at this horizon 
than in the lower beds that pitch at greater angles. In the 
town of Le Claire, on the west side of the main street, there is 
evidence of the erosion of the sea bottom by currents, and sub- 
sequent filling of the resulting channels v/ith material of the 
same kind as formed the original beds. In eroding the 
observed channel some of the previously formed layers were 
cut off abruptly, and in refilling the space that had been scooped 
out the new layers conformed to the concave surface and 
lapped obliquely over the eroded edges of the old ones. 
The angle at which the lower, more highly inclined beds 
stand never exceeds twenty-eight or thirty degrees; that is, it 
never exceeds the angle of stable slope for the fine, wet, cal- 
careous material of which the strata v/ere originally composed. 
The Le Claire limestone is, as a whole, sharply set off from 
the deposits of the Delaware stage by its hard, highly crystal- 
line structure, its freedom from chert, its easily recognized 
