THE WARSAW BEDS 71 



has arisen largely from the assumptions made at the place 

 most thoroughly studied by the respective authors, without 

 due allowance being made for the varying conditions in distant 

 localities. A careful comparison of notes and a somewhat 

 extended study in the field show that the term "Warsaw" has 

 been very loosely applied since its original appearance as a 

 geological name. In the majority of places the so-called 

 Warsaw is clearly the lower part of the Saint Louis limestone. 

 Thus the writers above alluded to were perfectly correct in 

 contending that the "Warsaw," as they understood it, was really 

 a portion of that formation ; but it was a mistake to claim this 

 for the " Warsaw" of all localities. It is apparent, then, that 

 in some places the so-called Warsaw cannot be separated from 

 the Saint Louis limestone; in others it is best united with the 

 Keokuk. It seems best, therefore, to drop the term in its 

 application to a distinct section of the Lower Carboniferous, 

 or Mississippian series, with a rank equal to the other subdi- 

 visions h^re recognized. 



SAINT LOUIS LIMESTONE. 



Since first recognized by Shumard, little diflSculty has been 

 encountered in locating the Saint Louis limestone over a wide 

 stretch of country. Its northern border is several hundred 

 miles beyond any known exposure of Keokuk rocks. From 

 this limit nearly to the Missouri river the limestone is quite 

 thin ; but south of the latter point it rapidly thickens until in 

 Ste. Genevieve county, Missouri, it attains a measurement of 

 more than 300 feet, and still farther southward more than dou- 

 ble the thickness known in the state mentioned. The Ste. 

 Genevieve limestone, which Shumard differentiated from the 

 Saint Louis deposits near the mouth of the Aux Yases river a 

 few miles below the old village of Ste. Genevieve, appears to 

 be merely the upper part of the main group of strata ; and the 

 fossils contained fully substantiated this view. A character- 

 istic exposure is shown in the accompanying plate viii. 



An unconformity of the Saint Louis rocks upon the under- 

 lying strata in Iowa and in the adjoining portions of the neigh- 



