Review of the New York Geological Reports. 



307 



Vanuxem gives the following figures in his Report, as most 

 characteristic of the Clinton group in his district. 



Plate 19, p. 77, Vanuxem's Report. 



Plate 19, fig. 1. Fucoides hilohata. 2. Tail oi Hemicrypturus. 

 3. Crinoidal joint. 4. Lingula ohlonga. 5. Strophomena de- 

 pressa. 



Fossils resembling figs. 1 and 3, have been found by Dr. 

 Locke in Ohio. The latter is very abundant in " the flinty stra- 

 tum" between the cliff and blue limestone of Adams County ; 

 but the bilobed Fucoid much lower, in the blue limestone for- 

 mation at Cincinnati. It may very possibly be a distinct species. 



Niagara Group. (A part of No. 6, if recognized in the Penn- 

 sylvania survey.) — This group consists of shale below and Hme- 

 stone above. The latter, in the eastern part of the state, is thin, 

 dark colored and concretionary, presenting many curious forms 

 and appearances represented in the Reports. Westward, it grad- 

 ually thickens into an important calcareous mass. From the 

 crumbling nature of the shale beneath, an undermining action is 

 observable wherever the group is exposed, and the capping of 

 hard limestone at first projects in overhanging ledges j at last 

 the poised mass, for want of adequate support, is precipitated 

 into the abyss below. The retrocession of the falls of Niagara 

 is due to this cause. And not only here, but over the entire belt 

 of country where these two members of the Niagara group pre- 

 vail, wherever a considerable stream has cut a channel, it at last 

 terminates in a fall, before it winds its way to the succeeding 



