IOWA ACADEMY OF 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 all 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 lithological 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 conradi (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 with 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 were 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 



