294 C. R. KEYES — THE PRINCIPAL MISSISSIPPIAN SECTION. 



there is a good exposure showing the upper surface of the buff arenaceous 

 limestone to be water-worn and weathered ; and directly upon the eroded 

 rock rests 20 feet of brecciated limestone. Whether or not this point can 

 be regarded as a portion of an ancient land surface older than the St. 

 Louis limestone depends partly upon the results of further investigation 

 and partly upon the final decision as to the origin of the brecciated rock. 

 At Hall's typical locality it is manifest that the Warsaw beds are 

 I u'opeiiy the superior portion of the Keokuk limestone. This inference is 

 directly derivable both from the faunal and stratigraphical features, and in 

 a less marked degree from the lithological nature of the deposits. The 

 layers passing under this name reported from other localities are now 

 known to have various relationships with the overlying and underlying 

 strata. Alleged faunal peculiarities have usually been the chief grounds 

 for considering the Warsaw as a distinct subdivision of the lower Car- 

 boniferous. Most writers on the subject have united the beds under 

 discussion with the St. Louis; a few with the Keokuk. This difference 

 of opinion has arisen, largely from assumptions made at the places most 

 thoroughly studied by the respective authors, without due allowance 

 being made for the varying conditions in separated localities. A careful 

 comparison of notes and a somewhat extended stud)' in the held show 

 that the term "Warsaw" has been 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 St. Louis limestone. Thus the 

 investigators above alluded to were perfectly correct in contending that 

 the '* Warsaw," as they understood it, was really a portion of the St. 

 Louis. But they made the mistake of claiming that the Warsaw of all 

 localities is St. Louis. It is apparent, then, that in some places the 

 so-called Warsaw cannot be separated from the St. Louis limestone ; in 

 others it is best united with the Keokuk. It seems better, therefore, to 

 drop the term in its application to a distinct section of the lower Car- 

 boniferous, or Mississipian series, with a rank equal to the other sub- 

 divisions here recognized. 



'to* 



St. Louis Limestones. 



Since first recognized by Shumard, little difficulty has been encountered 



in locating the St. 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 lime- 

 stone is quite thin; hut 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 southeastward more than double the thick- 



