The Le Claire Limestone. 



By SAMUEL CALVIN. 



The Le Claire limestone constitutes the second stage of 

 the Niagara formation as it is developed in Iowa. The first 

 or lower stage has been called the Delaware from the fact 

 that all its varying characteristics are well exhibited in Dela- 

 ware county. The Delaware stage embraces many barren 

 beds, and presents a very great number of phases, but at cer- 

 tain horizons it abounds in characteristic fossils. The typical 

 faunas of this lower stage embrace such forms as Pentamerus 

 oblongus Sowerby, Halysites catenulatus Linnteus, Favosites 

 favosiis Goldfuss, Stronibodes gigas Owen, Stromhodes -penta- 

 goniis Goldfuss, Ptyclwphyllum expansuni Owen, and Diphy- 

 ■phylluiii miiUicauIe Hall. The beds of the Delaware stage 

 furthermore contain large quantities of chert. 



The Le Claire stage of the Niagara follows the Delaware. 

 The exact line of separation between the two stages has not 

 been, and cannot be, definitely drawn. There are massive, 

 barren, highly dolomitized aspects of both stages that, taken 

 by themselves, cannot be differentiated in the field. Under 

 such circuinsances the observer must work out the strati- 

 graphic relations of the particular group of strata under .con- 

 sideration before referring it to its place in the geological 

 column. In general the Le Claire limestone is a heavy bed- 

 ded, highly crystalline dolomite. It contains scarcely any 

 chert, and in its lower part there are very few fossils. There 

 are occasionally a few specimens of Pentamerus of the form 

 described as Pentamerus occidcntalis Hall, and the principal 

 coral is a long slender, tortuous Amplexus which is represented 



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