128 Kindle — Unconformity at the Base of the 



whether it proceeded very slowly and chiefly in the direction of 

 the oldest rocks exposed at the base of the unconformity. The 

 latter view seems to have been maintained by some geologists 

 as a corollary of the dogma of very slighi erosion of Silurian and 

 Devonian lands. The photographs and other evidence here 

 presented indicate the necessity of very materially modifying 

 this assumption. It is of course possible to have had a south- 

 erly transgression of the black shale across Kentucky at the 

 close of such a cycle of erosion as has been indicated in this 

 paper, but proof of this must rest on evidence of distinctly dif- 

 ferent age values of the basal faunas of the black shale at 

 the north and at the south. It is desirable here to ascertain 

 just what evidence there is, if any, for such differences in the 

 age of the shale. Prof. Edward Orton, Jr.,* appears to have 

 been one of the first to claim that the black sh&le in Kentucky 

 represented only the " Upper or Cleveland Division " of the 

 Ohio shale. His statement is as follows : " The shale that 

 covers the Lower Silurian limestone in central Kentucky is the 

 Upper or Cleveland Division." This opinion concerning the age 

 of the Chattanooga shale is comparable to some which have 

 followed it in the poverty of evidence on which it rests and 

 the positive phrasing which might mislead one unfamiliar with 

 the subject to suppose that it represents an established fact. 



No complete or entirely adequate discussion of the time 

 interval represented by the unconformity at the base of the 

 Chattanooga shale can be given until the fauna and strati- 

 graphy of this formation have been described in detail. 

 Although generally considered to be nearly barren of organic 

 remains, the writer has found the carbonaceous beds of the 

 Chattanooga shale to carry a conodont fauna which is quite 

 as abundant in the lower or Huron shale of Ohio and Kentucky 

 as it is in the upper or Cleveland shale. These minute but 

 beautifully preserved fossils may be obtained at any locality 

 and at any horizon in the black shales from Lake Erie to 

 Alabama. These fossils have long been known in Ohio in the 

 upper beds of the Ohio shale, but with the exception of a very 

 few species have remained undetermined and undescribed. 

 When they have been described and the species which are con- 

 fined to the upper and lower horizons of the shale distinguished, 

 they will prove an invaluable aid in correlating the different 

 parts of the Ohio shale in Ohio with their equivalents in the 

 Chattanooga shale in Kentucky and farther south. Until this 

 has been done, however, any attempt to make use of these 

 fossils in correlating subdivisions of the Ohio and Chattanooga 

 shale must be considered premature and futile. Hence, in the 

 present discussion of the age of the interval represented by the 

 *Geol. Survey of Ohio, vol. vii, p. 23, 1893. 



