DEVONIAN. 277 



Foerste notes another occurrence, 4 miles north of Bakerville, where a limestone 

 3 feet thick has yielded HeUophyllum and Blothrophyllum, closely resembling forms 

 in the "Corniferous at the Falls of the Ohio, Louisville, Ky." Several species of 

 Cystiphyllum, Cyathophyllum, and Cladopora, a very large form of Atrypa reticularis,, 

 and Reticularia Jimbriata were found. These occurrences he correlates with the 

 Jeffersonville limestone of Kentucky and Indiana, regarded as the equivalent of the 

 Onondaga limestone of the East. 



The Chattanooga shale and its members, the Hardin sandstone and the" Maury 

 green shale of Safford, in western Tennessee are described by Hayes and Ulrich "'° 

 as follows : 



Excepting the bottom and top, which will be described separately, the mass of this formation 

 is a nearly black, rather tough bituminous shale, splitting generally into thin plates. It is the 

 well-known and sharply defined formation so often called the Black shale. The formation as a 

 whole is' remarkably persistent in its distribution, being found nearly everjrwhere in Tennessee 

 and adjoining Stateg to the south, west, and north, where its proper horizon is exposed. Its 

 occasional absence is due either to nondeposition or to erosion preceding Carboniferous deposition. 

 Generally throughout middle Tennessee there is at the base of the formation a thin bed which 

 is entirely different in character from the black shale above. In the western part of the Columbia 

 quadrangle, particularly in the valley of Swan Creek, this bed consists largely of calcium phos- 

 phate and forms the source of the Tennessee black phosphate. Its appearance varies somewhat 

 from place to place, as well as its chemical composition. It may be gray, bluish black, or black 

 in color, and it may be composed of grains large enough to be seen by the naked eye or may have 

 a dense, fine-grained structure. When examined with the glass small oval grains are generally 

 found to be more or less abundant, sometimes making up the mass of the rock. These have 

 polished surfaces and a brown or amber color. In many cases they are the casts of minute coiled 

 shells. The phosphate bed passes by gradations laterally into a bed of coarse sandstone or 

 conglomerate containing varying amounts of phosphaite. The grains are in part phosphatic 

 ovules and in part quartz, with less abundant waterworn fragments of other rocks and fish bones. 



The phosphate bed is also replaced, particularly toward the southwest, in Hardin, Wayne, and 

 Perry counties, by a fine-grained gray or black sandstone, which reaches a maximum thickness 

 of 12 feet in Hardin County, where it has been called the Hardin sandstone by Safford. It may 

 consist of a single massive bed or may have a shaly structure, and is generally more or lesa 

 phosphatic. 



It is evident that the black phosphate, the conglomerate, and the fine sandstone are merely 

 three phases of the same member of the Chattanooga formation and represent deposition during 

 approximately the same time, their difference in composition being due to differences , in the^ 

 sources from which their materials were derived. Occasionally, and this is particularly true of 

 areas in which the Chattanooga formation rests on the Clifton and Fernvale formations, the: 

 conglomeratic phosphate layer is replaced or represented by black shale hke that making up the 

 body of the formation. Except in these cases the basal bed everywhere follows a more or less 

 easily determined unconformity, and was deposited over a nearly submerged land surface. This 

 subsidence began in the Oriskany and, continuing through the Onondaga and Hamilton ages, 

 resulted finally in the submergence of the whole of the middle Tennessee dome. This sub- 

 mergence occurred in the Portage and continued through the Chemung, these late Devonian 

 ages being represented by the Chattanooga shale. 



At the top of the formation there is very generally a thin stratum of greenish shale and 

 earthy sandstone, which has recently received the designation "Maury green shale" from 

 Prof. Safford. He says it ranges "from a few inches to 4 or 5 feet in thickness;" but so far as 

 our observation is concerned, it does not exceed 2 feet in this area and usually varies between 

 12 and 18 inches. Nearly always this green shale has embedded in it smooth dark nodules or 



