354 



On the Silurian Basin of Middle Tennessee. 



8. The rocks of Middle Tennessee, equivalent to the "Blue 

 limestone" around Cincinnati^ and to the Hudson River, Trenton 

 and Black River Groups of New York, are about five hundred 

 feet thick. They comprise the first two groups, whicli, though 

 having characters in common, are upon the whole natural, and 

 separated by a well defined horizon. The lower of these and 

 the first of our series is the 



I. Stones River Group. 



9- This group is so named from the name of the stream along 

 "which it is finely developed. It is limestone throughout, and 

 from 240 to 260 feet in thickness. We have divided it, for con- 

 venience, into three members, though a more natural arrange- 

 ment would unite the first two. 



10, {a, ) Stones River beds, — This includes a series of blue and 

 brownish-blue limestones, mostly fine-grained and thick-bedded, 

 some strata of which abound in dark flinty layers. These rocks 



the oldest of Middle Tennessee — are about seventy-five feet 

 thick, and form an irregular circle, with a diameter of ten or 

 twelve miles, constituting the summit of the denuded dome in 

 Rutherford, {§ 3.) The member differs from the one next 

 above in its thick-bedded strata, and in not affording as many 

 fossils, which, (together with the comparatively less study be- 

 stowed upon it,) will account for the paucity of species. The 

 following is a list of those observed and collected; it will be 

 seen that nearly all are common to ihe member succeeding. 



# 



1. Stromatocerium rugosum, HalL 



2. Ortliis bellarugosa, ConracL 



3. Atrjpa liemiplicata, Hall 



4. " recurvirostra ? Hall. 



5. Lcpttena, allied to L. incra==?ata 



6. Plcurotomaria umbilicata, HalL 



7. Gonioceras anceps, Hall !f 



8. Actiuoceras teauifilum, Hall. 



11. (b.) Loioer Lebanon limestone. — The irregular circle just 

 mentioned is surrounded by a broad zone of thin-bedded layers, 

 which — everywhere attended by ^' cedar glades" — sweeps off in 

 opposite directions, reaching the Cumberland on the north, and 

 Dnck River, along w:hich it spreads, on the south. This thm- 

 bedded sub-group is from fifty to sixty feet thick and 

 deveIoi>ed in and about Lebanon, which locality has afforded 

 most of the species enumerated. The sky-blue layers — some- 

 times separated by seams of argillaceous matter — are coarsely 

 crystalline and abound in calcareous remains. 



is w 



ell 



* All of the species given in this paper, with very few exceptions, have eit 

 been collected, or seen by myself, in situ, and it affords me pleasure to state, tn^tt 

 comparing and making them out, I am greatly indebted to the valuable assistsui^ 

 of so able a Palaeontologist as Prof. James Hail »tw>*'' 



f Tlie relative abundance of species when cpnsiderable is expressed as follotr 

 T'ery abundant 1!I — abundant !! — common ! 



! 





