PAIN.] DEVONIAN AND CARBONIFEROUS ROCKS. 19 



pebbles of black material, probably phosphate of lime. There is also 

 a certain amount of a green, flaky material, probably glauconite. 

 This bed is very thin and was observed at only one point. 



Thickness. — The total thickness of the formation is unknown, as 

 its bottom is not exposed and there are no drill holes passing through 

 it. A careful estimate was made by Mr. Ulrich and the writer; at 

 least 50 feet are exposed, and probably 100 feet or more are pres- 

 ent. It is difficult to make an exact estimate owing to imperfect 

 exposures and variable dips. 



Distribution. — No exposures of the shale are known except in the 

 vicinity of Hicks, in Hardin County. The shale here outcrops over 

 iwo areas, as indicated on PI. III. It is found here in the bottom of 

 streams, but is covered by younger rocks of the hills. It occiu-s in a 

 series of exposures showing dips outward from a common center and 

 indicating that it is brought to the surface in a low dome. The gen- 

 eral relations are indicated on the special map of the Hicks area and 

 in the cross section from Rosiclare to Karbers Eidge (PI. IV). 



Name. — In the older publications this shale was referred to merely 

 as the Devonian black shale. It is believed to be the equivalent of the 

 Chattanooga shale of Tennessee, the New Albany shale of Indiana, 

 and the Ohio shale of Ohio. The latter, being the oldest geographic 

 name used for it, is adopted in the present discussion. 



CARBONIFEROUS ROCKS. 

 TULLAHOMA FORMATION. 



Character. — The Tullahoma, as developed in Hardin County, con- 

 sists for the most part of flint or chert. It includes some shale and 

 a subordinate amount of nonmagnesian limestone, but the latter is 

 rarely exposed, as it has usually lieen dissolved, and merely a gentle 

 talus slope of flint fragments remains. Mr. Ulrich, in discussing 

 the formation as developed along Hicks Branch, recognizes the fol- 

 lowing divisions : 



In the basal 50 feet the shales preflouiiiiate in the ratio of about 2 to 1. In 

 the next 50 feet the layers of shale and chert constitute about equal propor- 

 tions of the mass, while an occasional layer of limestone is intercalated. In 

 the third 50 feet the shale decreases to little or nothing, while the chert and 

 limestone bands alternate and are about equally important. In the fourth 50 

 feet shales are practically absent, the limestone has become somewhat heavier, 

 though irregularly bedded, and the chert is proportionately less abundant. At 

 the top there are 2.^> feet or moi-e of slightly cherty, light-colored, massive 

 or laminated limestone, containing fenestellid Rryozoa. 



In this report the line between the Tullahoma and the St. Louis 

 is drawn at the top of these beds or at the lowest ledge marked by 

 the connnon presence of the easily recognized coral Lonsdalia {Litho- 



