A SKETCH OP GEOLOGY. 19 



been closed by a cataclysm, extinguishing all life of the Silurian time, Nature 

 itself would have drawn a dividing line between Silurian and Devonian forma- 

 tions which could not be misunderstood by anybody ; but no cataclysm ever 

 took place ; on the contrary, the transformation of the Silurian fauna and flora 

 into their Devonian forms was accomplished by slow and gradual modifications, 

 a process which did not produce partition lines, the establishment of which is 

 thus left to arbitration. The proper way to find out the correct position of the 

 Oriskany sandstone, is to carefully examine its fossils ; if these show a nearer 

 relationship to those of the Devonian than to the Silurian, the questionable 

 group belongs to the younger formation ; but if the relationship is closer to the 

 Silurian forms, said group should be transferred to the Silurian column. In 

 our own State, we find the Devonian formation represented only by the upper 

 Helderberg and Hamilton groups, which are so blended together that it is en- 

 tirely impossible to separate them from each other. Fossils characteristic of 

 either of these groups are found from bottom to top of the whole Devonian 

 columns in Kentucky. The Devonian formation does not cover a very extensive 

 field in our State, still it is of great importance for economic, as well as for 

 scientific purposes. It furnishes to the builder rock, cement and lime ; to 

 the farmer, a healthy and productive soil ; and to the geologist, those pre- 

 cious specimens of fossil corals, crinoids and shells, which nowhere on the whole 

 globe can be found in such abundance of specimens and species, and in such 

 excellent state of preservation, as at Louisville and its vicinity. The widely 

 known Falls of the Ohio River are not only known here in this country as an 

 obstruction to navigation, but they are known to geologists of the whole civil- 

 ized world as the great store-house where the Devonian world has collected the 

 choicest specimens of its animal kingdom. 



The Upper Helderberg group is often called the Corniferous limestone, or the 

 Corniferous group, on account of the great mass of hornstone which it contains. 

 This hornstone is found in great abundance in all of our Devonian strata, and 

 it would, therefore, be advisable to designate the whole Devonian column in 

 Kentucky as the Corniferous group. 



CARBONIFEROUS FORMATION. This formation is divided into Subcarbonifer- 

 ous and Coal Measures; both are still covering a large territory in Kentucky, 

 though it appears that their former original extent has been greatly reduced by 

 denudation. At present we have two large coal fields in our State ; the eastern, 

 which forms a part of the Appalachian coal region, and the western, belonging 

 to the Illinois coal fields. Both these districts, it appears, were formerly 

 united, though they are at present separated from each other by a broad strip 

 of land whose surface-rocks belong either to the Devonian or to the Silurian. 

 That the Carboniferous strata originally covered this dividing strip can scarcely 



