360 



Oil the Silurian Basin of Middle Tennessee, 



isj from top to bottom, soft, yellow, siliceous or sandy shale, 

 with heavy interstratified layers of hornstoiie. 



The rock is generally thinly doited with siliceous — sometimes 



calcareous — concretions 



the larger occurring in the upper, mora 



with 



calcareous portion, are often fine geodes of quartz lined 

 crystals ; one locality, at least, affords rhombohedral forms. 



An interesting feature of these rocks 



—in fact of the group — 

 is the presence of Crinoidal limestone. It occurs at various ele- 

 vations in intercalated beds, ranging from one to ten feet in thick- 



ness ; some of these are pure grayish-white limestone made up 



of the crinoidal remains; others are impure and enclose silicified 

 fossils. As might be anticipated, the Crinoids are the most 

 abundant fossils. The silicified ones are found occasionally in 

 place, but usually detached, on the hill-sides with the flinty frag- 

 ments, and in the soil ; silicified Trochites of a large size, both 

 circular and oval, — common also to the succeeding member, 

 are found in many places. 



Large Spirifers and Producti occasionally occur, but excepting 

 perhaps Crinoids, fossils are not abundant, the conditions under 

 which the rocks were deposited not having been favorably to 

 animal life. 



List of Species. 



1. Gyathopliyllum, sp. ? 



2. Streptelasma, n. sp. . 



3. Actiiiocrinus Agassizii, Troost. 



4. 



tt 



uriia, " 



5. 



u 



cornutus, " 



6. 



a 



HmnljolJtii, « 



1. 



u 



Mariner!, " 



8. 



u 



I^asLvillensis, " 



9. 



(( 



fibula, « 



10. Synbathocrinus Tennesseae, Troost! 



11. Catyllocrinus Tennessese, 



12. Cyathocrimis pentaspliericus, 



u 



ti 



IS. 



jl 



corrugatus. 



u 



u 



t 



! 



14. Conocrinus tuberciilosus, 



15. Agaricocrinus tuberosus, 



16. Spirifer allied to attenuatus. 



11. Producti and other shells not described, 



As we approach the topmost strata, the rocks, without afford- 

 ing any well marked limit, gradually run into 



20. (6.) Cherty limestone. — This member though related to the 

 last, differs in being a true limestoncj in affording a brick-red soil, 

 in the character of its imbedded masses, and in being much more 

 fossihferous. The fundamental rock is thick-bedded and impnrej 

 of a light blue color; it occurs occasionally in purer beds with- 

 out flints, but, in the main abounds in reniform nodules of chert 

 and in siliceous layers. The latter, which, by the way, are very 

 characteristic, liberated by the removal of the calcareous matter 

 that contained them, occur very generally on the surface and m 

 the red soil, in rough /rzai/e masses having di porous sandy struc- 

 ture and a light yellow or gray color ; they abound in species of ^ 

 the beautiful Fenestella^ and often in a large undescribed (?) OrthiS; 



as 



1 



The strata are sufficiently argillaceous to give the soil a clayey 



t 



I 



consistence. 



