Chattanooga Shale in Kentucky. 127 



deeply incised, have removed it altogether. The very irregular 

 and patchy distribution of theDevonian limestone which obtains 

 in southern Kentucky and adjacent parts of Tennessee, taken 

 in connection with the evidences of its partial erosion in central 

 and northern Kentucky, strongly suggests that this formation 

 has been completely removed over a considerable area near the 

 Kentucky-Tennessee line and over smaller areas in central 

 Kentucky. In the latter area the Devonian limestone is gen- 

 erally present where the Chattanooga shale is found, but over 

 certain areas, as the regions between Bardstown and New 

 Haven, between Ray wick and Loretta, and south of Stanford, 

 it is entirely absent. Farther south it is not the absence but 

 the presence of the Devonian limestone which is exceptional, 

 Southwest of the southern limit of the Devonian limestone in 

 Kentucky, as indicated on Foerste'sf map, a detached area of 

 this formation occurs on the Rolling Fork River. The writer 

 has found another on the Green River near Edith P. O. A 

 third occurs south of the Tennessee line on the Harpeth River. 

 In the light of the evidence which has been presented of the 

 extensive denudation of the Devonian limestone at Irvine, it 

 appears nearly certain that these outlying patches of limestone 

 are remnants of a once continuous sheet of Devonian limestone. 

 Its relatively greater degree of denudation is doubtless the 

 result of the greater elevation of the axis of the Cincinnati 

 geanticline in southern Kentucky and northern Tennessee. 



Time interval represented. — Any conclusion concerning the 

 time interval represented by the unconformity which has been 

 described must rest upon the determination of the age of the 

 formations involved. The complexity of this question is 

 apparent when we consider that the unconformity iuvolves at 

 its base at least six distinct formations in Kentucky ranging in 

 age from Ordovician to Middle Devonian. This, of course, 

 raises the question whether in one part of the area land con- 

 ditions began as early as Ordovician and in another part as late 

 as post-Hamilton time, or whether differential erosion is respon- 

 sible for the difference in age. The evidence already given of 

 the nearly complete denudation of the Devonian limestone by 

 subaerial erosion at one locality seems to strongly support the 

 probability that the absence of the later formations in part of 

 the Kentucky area is due to denudation rather than to land 

 conditions having persisted in certain areas from Ordovician 

 to the beginning of Chattanooga sedimentation. Obviously the 

 question of transgression or overlap comes into the problem. 

 But we have to discover whether the transgression proceeded 

 rapidly and at approximately the same rate from all sides, or 



* Silurian and Devonian limestones of Tennessee and Kentucky, Bull. 

 Geol. Soc. America, vol. xii, fig. 8, 1901. 



