242 



TRANSACTIONS OF THE 



This encrenitic stratum is followed by a very interest- 

 ing silico-calcareous one, or a stratum, which is at some 

 places entirely calcareous, at other places entirely silici- 

 ous, and at other places again, the silicious and calcare- 

 ous strata alternate with each other ; the silicious parts 

 have sometimes the appearance of hornstone or chert, 

 sometimes of sandstone, and have often an earthy aspect 

 resembling tripoly, but whether calcareous or silicious, 

 the v^^hole stratum, which is from 200 to 300 feet thick, 

 is characterised by some reticulating polypifers, resemb- 

 ling the Gorgonia antiqua, Goldf., G. infundibuliformis, 

 Goldf. ; also the Retepora cancellata, R. prisca, both of 

 Goldf. I have specimens, the calcareous parts of which 

 are entirely made up of them, and I have also silicious 

 specimens which are similarly composed. It is this stra- 

 tum which contains our rich deposits of hydrate of iron ; 

 even the cavities which are in the ore, are sometimes 

 filled with the above mentioned Gorgonia and Retepora, 

 in a silicious state. 



This stratum is covered, towards the west of Tennes- 

 see river, by strata of sandstone, which contains lignite 

 and immense beds of marly limestone, which contains 

 Ostrea falcata, Exogyra costata, Gryphsea convexa, G. 

 mutabilis, all of which have been described by Dr Mor- 

 ton and others, and which stratum will be described more 

 minutely in my geognostic description of the state, but 

 our present intention is to follow up the stratification 

 towards the Big Bone cave. ■ 



The silico-calcareous stratum, with Gorgonia, &c., 

 described above, and which forms the high, but level 

 part of Davidson, Williamson, Maury, Rutherford, War- 

 ren and White counties, is in the eastern parts of the 

 two latter counties. Warren and White, covered with a 

 different series of strata. It is an alternation of different 

 strata of limestone : some black, resembling the black 

 marble of Dinant and Nameur, in the Netherlands; 



