ig. NATURAL HISTORY BULLETIN. 



only by casts of the vacant or hollow parts of the original 

 corallum. On account of the complete solution of the original 

 structure the spaces occupied by the solid parts of the corallum 

 are now mere cavities in the limestone. In the upper part of 

 the Le Claire stage small brachiopods abound. They be- 

 long to the genera Homeospira, Trematospira, Nucleospira, 

 Rh3mchonella, Rhynchotreta, Atrypa, Spirifer, and probably 

 others. In most cases the fossils have been dissolved out, and 

 they are now represented by cavities in the limestone. The 

 calcareous brachial apparatus of the spire- bearing genera is 

 often perfectly preserved, and is the only part of the original 

 structure left. No statement can well give any idea of the 

 numbers of the small shells that crowded the sea bottom near 

 the close of the Le Claire stage, nor of the corresponding 

 number of minute cavities that are now so characteristic a 

 feature of this portion of the Le Claire limestone. In some 

 localities in Cedar county the small brachiopods of this horizon 

 are represented by very perfect casts that were formed by a 

 secondarv filling of the cavities left by solution of the original 

 shell. The external characters are thus fairly well reproduced. 



Compared with the beds of the Delaware stage, the Le 

 Claire limestone as a rule lies in more massive ledges, it is 

 more completely dolomitized, and its fracture surfaces exhibit 

 a more perfect crystalline structure. It contains an entirely 

 different fauna, a fauna in which small rhynchonelloid and 

 spire-bearing brachiopods are conspicuous. Its fossils are 

 never silicified, and, in marked contrast with some portions of 

 the Delaware, its upper part at least is notably free from 

 chert. The Le Claire limestone is the lime-burning rock of 

 Sugar creek. Cedar Valley, Port Byron and Le Claire. 

 Wherever it occurs it furnishes material for the manufacture 

 of the highest quality of lime. 



With respect to their distribution the strata of this stage are 

 well developed at Le Claire in Scott county. The\' are seen 

 in the same stratigraphic relation at the lime kilns on Sugar 

 creek, and at Cedar Valley in Cedar county. They occur 

 beneath the quarry stone at, and near, Stone City, Olin, and 



