THE LE CLAIRE LIMESTONE. 



189 



the main street, there is evidence of the erosion of the sea 

 bottom by currents, and subsequent 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 lavers 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. 1 Plate II.. Fig. i. ) 



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 originallv 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 

 fauna, and its record of anomalous conditions of deposition. 

 In the field the distinction between the Le Claire and the 

 Anamosa statues are even more easilv recocjnized. though 

 aunally the two stages are intimately related. In the Ana- 

 mosa stage oblique bedding is unknown, lithologically the 

 rock is an earthy, finely and perfectly laminated dolomite, not 

 highly crvstalline in its tvpical aspect, and too impure for the 

 ^manufacture of lime. It may be quarried in s\-mmetrical 

 blocks of anv desired dimensions, while the Le Claire lime- 

 stone breaks into shapeless masses wholly untit for building 

 purposes. The quarrv beds of the Anamosa stage are quite 

 free from fossils, but along the Cedar river in Cedar county 

 the brachiopod fauna of the upper part of the Le Claire re-ap- 

 pears in great force in a stratum four feet in thickness, up 

 near the top of the formation. The beds of the Anamosa 

 stage are very undulating and dip in long graceful sweeping 

 curves in everv possible direction. The knobs and bosses 

 and irregular undulations developed on the sea bottom as a 

 result of the peculiar conditions prevailing during the Le 

 Claire age. persisted to a greater or less extent after the age 

 came to an end, and it was upon this uneven floor that the 

 Anamosa limestone was laid down. (^Plate II., Fig. 2.) 



