636 GEOLOGY OF OHIO. 



now described from the Huron shale of Ohio. Both were of great size 

 and great power. Very full and interesting descriptions of them are 

 given in the volumes of Paleontology already issued by the Survey. 



Aside from the contents of these concretions, the Huron shale of Frank- 

 lin county, may be described as nearly non-fossiliferous.. One may look 

 for hours on great banks of the shale, without finding a trace of vegetable 

 or animal structure. The only forms known to occur are the following : 

 On the surface of the layers, strap shaped impressions of marine plants, 

 are occasionally found. In rarer instances, a thin film of coal represents 

 the vegetable tissues. In the ivaste of the slate, silicified coniferous wood 

 is often found, but it is believed that this is generally derived from the 

 breaking down of the concretions alread}' noticed, of which it often con- 

 stitutes the nucleus. Of course it is quite possible that blocks of this 

 ancient wood may have been preserved in the slate, without gathering 

 around them concretions, but no specimen has been found in situ thus far, 

 except in concretions. 



Towards the upper limit of the slate, several localities have been found 

 in which the teeth and rhombic plates, black and shining, of small ganoid 

 fishes have been found. These agree almost exactly with the fossils of 

 the same group from the Cleveland shale — a formation that is also identi- 

 cal in lithological characters. The best point for collecting these rare 

 forms, is in the fine exposures of the shale in the valley of Big Walnut, 

 near Central College, Blendon township. 



A fine specimen of the crest of teeth peculiar to the dentition of Ony- 

 chodus, was obtained from the shale of Slate Run, in Perry township, by 

 Mr. W. Meteer, and was by him presented to the State collection. It 

 has not been finally determined, but Dr. Newberry considers it to be 

 Onychodus HopMnsi, or else an undescribed species. The species referred ' 

 to, 0. Hoplcinsi, was described from the Chemung group, of New York. 

 The horizon of this specimen can not be definitely given, but it is with- 

 in forty feet of the bottom of the series. 



Such facts as these, while they illustrate the poverty of the formation 

 in fossils, still justify considerable geological interest in it. It is to be 

 remembered, that the formation is shown almost altogether by natural 

 exposures. There is little to lead to its being worked for economical uses. 

 Our knowledge of the great wealth in fossils of the Corniferous limestone 

 would be very meagre, if we had not access to the extensive qfiarries 

 where fresh exposures of all its strata are seen. Whatever fossils are 

 found in the shale q.re quite likely to be either new species or species not 

 heretofore found in Ohio; for the three hundred feet of this formation 



