44-2 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



character, mineral contents, and even proximity to the coal-mea- 

 sures, the " Scar limestone " of England ; and how readily, were it 

 not for the guide furnished by organic remains, it might be mistaken 

 for its equivalent. 



The thickness of these limestone beds is various : in the south- 

 ern part of Ohio it is seldom more than 80 or 100 feet ; in the 

 southern part of Indiana it is from 150 to 200 feet; while in Iowa 

 and Wisconsin, as we have seen, it is upwards of 500 feet. It at- 

 tenuates towards the south ; so thin, indeed, and altered in its ap- 

 pearance is this rock in Middle Tennessee, that were it not for the 

 test furnished by organic remains, it would be difficult to recognise 

 it at all. Dr. Troost has included this and the succeeding group in 

 one; but the difference in lithological character and mineral con- 

 tents, where they are well-developed, fully warrants a separation. 



Though not uniformly rich in organic remains, many of the beds 

 of the group in question are highly fossiliferous. The Catenipora 

 escharoides is very abundant in its upper beds in Iowa, and so are 

 Pentamerus huspodus and P. ohlongus (?)*. 



Next in importance and character are Aulopora tubcBformis(l)\, 

 Go\&t, Sarcimda organum, Lam., Favosites Gothlandica (?), Goldf., 

 F, basaltica, Goldf., F. spongites, Goldf., F. fibrosa, Goldf., F.poly- 

 morpha, Goldf., besides some undetermined species, perhaps new ; — 

 Syringopora verticillata, Goldf., Cyaihophylliim vermicidare (?), 

 Goldf., C.turbinatum, Goldf., Strombodes astroides, nobis, Lu?iulites 

 dactylioides^ nobis, Astrea, Lingula, Orthoceratites, Conitites, Del- 

 phinula (?). 



Many beautiful and characteristic fossils of this group have been 

 found at the Falls of the Ohio near Louisville, where some of its 

 members form the bed of the stream. In the uppermost stratum, 

 the one on which the water-limestone of the previous group rests 

 (designated by Dr. Clapp as the " shell-stratum "), have been found 

 Strophomena euglypha, Cardium alceformis, Atrypa prisca (the 

 same species as occurs in the superincumbent water- limestone); a 

 Delthyris with a very wide cardinal area; D.gregaria, Clapp, very 

 abundant and characteristic, besides several other species ; Bellero- 

 plion (species undetermined); a Peniremite, very different in form 

 from any of the species found in the Pentremital limestone; Favo- 

 sites hemisphcerica, Troost; Gorgonia, Retepora |, and Fenestella (?). 

 The stratum in which these fossils occur is, according to Clapp, six- 

 teen feet thick. 



Beneath it, in the ' Coralline strata ' of Clapp, whose thickness 

 is twenty feet, the fossils are mostly corals: viz. five or six species 

 of Favosites, Cyathophyllum gigas, Clapp (some individuals two feet 



* The fossils of this group are more apt than those of any other to occur in the 

 form of casts. 



t The difference I can perceive between this and the Aulopora tubceformis is, 

 that the terminal orifice in the Iowa fossil is obscurely star-shaped, while that of 

 the above coralline is not. 



X This Retepora resembles the R. fenestrafa, but is very much larger and the 

 pores are more numerous. I have named it Retepora Indianensis, 



