26 MISSISSIPPIAN BRACHIOPODA 



removed by erosion in pre-Pennsylvanian time, and in such, areas this 

 formation constitutes the floor upon which the Pennsylvanian beds have 

 been deposited. 



There is reason to believe that the Yankeetown rests unconformably 

 upon the subjacent Renault, since the immediately underlying strata are 

 in some localities limestone, in-others sandstone, and in still others shale. 



Padnt Creek formation Above the Yankeetown formation is a series of 

 strata approximating 60 feet in thickness, which are shales below, passing 

 into limestones above. Near the base of this Paint Creek formation, 

 either resting directly upon the Yankeetown or separated from it by a few 

 feet of blue or gray shales with perhaps some thin calcareous beds, is a 

 deep-red, clay member. Its summit is about 25 feet above the top of the 

 Yankeetown chert in a tributary of Paint Creek about five and one-half 

 miles northeast of Prairie du Rocher, from which locality the formation 

 name has been taken. In fresh exposures this red bed exhibits little or 

 no stratification; on being subjected to atmospheric agencies it first 

 crumbles into small, angular fragments which eventually disintegrate into 

 a fine, red mud. The appearance of the stratum is more that of a residual 

 clay than anything else familiar to the writer. It is a constant member 

 of the formation, being present throughout the entire extent of surface 

 outcrop of this portion of the Chester group, and being recognized in 

 deep-well records beyond this region. 



No fossils have been found in the red-clay member of the Paint Creek 

 formation, but in the succeeding calcareous shales and limestones fossils 

 are common in many localities. Like the faunas of the Renault, the Paint 

 Creek faunas are typically Chester in facies and contain many of the 

 species which have usually been reported from the "Chester" or "Kas- 

 kaskia" limestone in the past. The genus Archimedes is more commonly 

 present than in the Renault, although it is as a rule not abundant, as is 

 commonly the case in some of the higher beds. Lyropora is also a com- 

 mon form in some localities, and among the braehiopods Diaphragmus 

 elegans abounds in many places. 



Ruma formation. Succeeding the upper limestone member of the Paint 

 Creek is a shale formation, in which a thin sandy member is usually pres- 

 ent near or a little above the middle. These beds are most typically ex- 

 posed in some of the tributaries of Horse Creek northeast of Ruma, and 

 attain a thickness of 25 to 40 feet. The shales are in part variegated and 

 in part blue or gray, this being, in fact, the highest conspicuous horizon 

 of variegated shales in the Chester group. The shales have nowhere been 

 observed to be fossiliferous, but in the sandstone member of the forma- 

 tion, lepidodendroid tree trunks, probably identical with those in the 

 Renault, occur in many localities. 



