CHATTANOOGA BLACK SHALE 429 



phatic material was obtained. The greenish clay material, however, 

 belongs to the Waverly horizon, so that the base of the Waverly appears 

 to contain material derived from the eroded top of the Black Shale bed. 

 The crinoidal material is unquestionably of Waverly age. The fine- 

 grained but not fissile rock in the old Saw Mill hollow may also be of 

 Waverly age, since species of Chonetes of the same general form are 

 rather common at the base of the Waverly section in the northern part 

 of Giles county. The dark color of the rock may be due to carbonaceous 

 material received from the denuded Black shale of this area, while 

 the more sandy character may be due to material washed in from some 

 other source by the Waverly sea. The gradual passage of the black rock 

 upward into the greenish rock, as already described, is also favorable to 

 the view that the black rock, without good fissile cleavage, may be of 

 Waverly origin. In case these observations are correct, the absence of 

 the Black shale at the " Big hill " may be due, not to original lack of 

 deposition, but to subsequent erosion. 



Cause of thinness of Black shale in southern Tennessee. — So far as may be 

 determined from the sections studied, the Black shale diminishes in 

 thickness on passing from the most eastern exposures on the Cumber- 

 land river southwestward to the Harpeth River region of Tennessee. 

 Southwest of the latter stream this diminution is even more consider- 

 able and is quite general. An entire absence of Black shale is noticed 

 not only at the Big Hill section in the southern part of Maury county, 

 but also at various points in the eastern part of Lewis county, along 

 Helm fork, Bell branch, and northwest of Lucerne. 



A study of the Silurian-Devonian unconformity in Tennessee indi- 

 cates that the Cincinnati anticline had begun its development before the 

 deposition of the Black shale. Its trend may be determined across the 

 central part of the state. At its southern end it appears to have turned 

 more distinctly westward, and it is at this southern end of the Cincin- 

 nati anticline that the thinnest sections of the Black shale or the cases 

 of its entire absence occur. The question may therefore be raised 

 whether this thinning of the Black Shale section in southern Tennessee 

 is due to a marked development of the southern end of the Cincinnati 

 anticline at the time of the deposition of the Black shale and the base 

 of the Waverly. 



Source of the detrital material at base of Black shale. — There is also an 

 increase in the coarseness and often in the thickness of the sandy and 

 earthy material at the base of the Black Shale section on passing from 

 the most northeastern localities along the Cum'berland to regions west 

 of the anticline in southern Tennessee. This coarseness becomes suffi- 

 cient in many parts of Maury and Hickman counties to form a sort of 



