64 The Cincinnati Group. 



The exposure at Cincinnati was known for many years as the Tren- 

 ton Group, both at home and abroad. Prof. Hall, of New York, and 

 Sir Charles Lyell, both considered it as the equivalent of the Trenton^ 

 Later, however, Prof. Hall and others regarded it as the equivalent of 

 the Hudson River Group ; and, finally, during the progress of the 

 Geological survey of Illinois, Meek and Worthen proposed to desig- 

 ' nate it as the Cincinnati Group. The reasons urged by them seemed 

 to be satisfactory to all naturalists and geologists of the country, and 

 the name was quickly adopted by the Indiana and Ohio geologists. It 

 is now as firmly established as the name of any group belonging toauy 

 formation, and its signification as fully comprehended. 



The only subdivision of the Cincinnati Group, founded either upon 

 the stratigraphical appearance or fossil contents of the rocks that has 

 yet been ascertained, is marked by the wave-like rocks at an elevation 

 of about two hundred feet above low water-mark at Cincinnati, and 

 even such a subdivision would be, to say the least, of very doubtful 

 utility. These wave-like rocks are composed in a very large part of 

 fragments of crinoids, principally of the Ileteroainoiis simplex, and 

 appear to have been formed by the action of the waves in first break- 

 ing to j)ieces the animal skeletons, and then leaving them in ridges, as 

 if to mark for all future time the coarse of the waves. These rocks 

 are found in all the hills about Cincinnati, and as far east as Plainville. 

 They have not yet been examined with that care necessary to deter- 

 mine whether they all mark the same course, or substantially the 

 same course, of the waves, but many of them have a north and south 

 direction, thus indicating an east and west wave, if it be true that 

 they are the result of the action of waves. 



A number of fossils are found below these rocks that have thus far 

 not been found above them, and, on the other hand, many have been 

 found above that have not been found below. Among those found 

 below, ami not known above, are Triarthrus Beckii, Leptoholus lejy'is, 

 Modiolopm anodontoides, Ambonychia bellistriata, Orthis emacerata, and 

 the undescribed crinoid with the unusually smooth column. The fos- 

 sils found above that are not found below are too numerous to mention. 

 The fossils which are common to both elevations comprise more than 

 half of all those found below these rocks. And vet on further exam- 

 ination it may appear that the causes which led to the formation of 

 these ^^ aves on the rocks also caused a considerable change in the ani- 

 mals that inhabited the ocean at this place. At present, however, 

 there is too little known on which to base definite conclusions, or to 

 found a subdivision that would be of any advantage to the collector, 

 or to science. 



