170 Ulrich — Chattanoogan Series with Special Reference 



County in central Kentucky, where both formations are finally 

 lost. 



Sunbury shale. — The Sunbury may be quickly described as 

 a rather thin but extremely persistent bed of black fissile car- 

 bonaceous shale, usually much like the typical Cleveland in 

 general aspect. In Ohio it ranges in thickness from 6 to 

 nearly 28 feet. In Kentucky it is likewise very persistent 

 though considerably thinner, being in places reduced to less 

 than a foot. Since it is clear that the Sunbury followed differ- 

 ential tilting and warping of the continental basins that pro- 

 hibited deposition of the Bedford and Berea in the same 

 general area, it is inferred that this youngest bed of the 

 Chattanoogan black shales is gently overlapping in structure 

 and that these greatly reduced thicknesses on the east flanks 

 of the Cincinnati dome are ascribable to this cause. However, 

 I have seen small accumulations of ill-stratified soft clay with 

 phosphatic pebbles or nodules at the top of this Sunbury in 

 Kentucky, a condition that suggests a time break following 

 this shale and probably removal of some of its original thick- 

 ness by erosion. In Tennessee, more particularly in the west 

 middle part of the state, a similar break is indicated by the 

 Maury shale, a thin glauconite bed often filled with phospha- 

 tized concretions, that probably represents surficial decompo- 

 sition and subsequent recementation. This layer was referred 

 to the top of the Chattanooga by Hayes and Ulrich,* which is 

 correct if we consider chiefly the origin of its material. But 

 if the date of its recementation and the fact that its top 

 includes both reworked and transported material is brought 

 into the foreground, the layer becomes debatable ground. On 

 the latter grounds, I take it, Safford,f and more recently 

 Bassler,+ have classified the Maury shale as post-Chattanoogan. 

 There is, however, a practical objection to Safford's classifica- 

 tion of the bed, namely, that in the distance of a mile or two 

 the Maury would have to be placed at the base of two and 

 rarely, even three, distinct formations, which successively over- 

 lap the margins of the narrow embayments that indented the 

 shores of the Nashville island. Thus, in one case, the Maury 

 would be at the base of the Ridgetop shale, an early Kinder- 

 hookian formation ; in another, but a short distance away, the 

 New Providence — early Osagian in age — is the first to rest on 

 it, while in many other nearby places the recementation was 

 delayed to the advance of the Fort Payne sea. For this reason 



* Folio No. 95, U. S. Geol. Survey Atlas, 1903. 



fSafford, J. M. : Elements of Geology of Tennessee, 1900, pp. 104, 141. 



JBassler, E. S. : Proc. U. S. Nat. Museum, vol. xli, pp. 209-224, 1911. 



