>t 



* 



On the Silur-ian- Basin of Middle Tennessee. 357 



I 



Strata of whiter, more compact limestone, in some places eight 



feet thick and not granular as the last. Abov^e thesC; again, and 



separated by several feet of the ordinary limestone, follows the 



second interesting bed. It is peculiar in being of a yellowish 



gray color, in being almost entirely an aggregation of individuals 



of a Bucania^ Miirchisonia bicincta^ and of fine specimens of 



an undescribed Acephal^ and also in its porous character due to 



cavities formed by the grouping of the shells. The bed is from 



eight to ten feet thick and has been noticed by Dr. Troost in his 

 reports. 



In the following list of species, those which are confined either 

 to the upper or lower part are distributed accordingly. 



1' Strcptelasma, sp. und. Upper. 



2. ChiEtetes lycoperdon, Say. !!! 



3. " const ellata.YimcliiYQ. Upper!! 

 4' " columnaris, Hall. 



6. Favistella stellata, " 



6. Recoptaculites ? n. sp. 



7. Asti-oceriuai? n. sp. 



8. Stictopora, n. sp. 



9. Stromatoceriiim, n. sp, 

 10. Schizocrinus (steins.) 



U. Cyathocnnitesconglobatus^xoo'^t, Up. 



12. Aster las antiqua, Troost. Upper. 



13. Leptifina altemata, Conrad!!! 

 |4. « sericea, Sow. 



J^- ** planoconvexa, Hall. Upper, 

 16. OrtJtis shmata, Hall Upper!! 

 I*- " subjugata, " " !! 



18* " peetinellaj Conrad. 

 ^^' " undescribed. 



20. Spirifer Ijnx, Eich. !! 



21. Atrypa incrcbescens, Hall. !I! 



22. Atrypa niodesta, Say !!! 



23. AmhonycMa radiaia, Hall. 



24. Avicula deniissa^ Conrad. 



25. Two new gen. of Acephals. 



26. Pteurotomaria hilix^ Conrad. 



27. « n. sp. 



28. Mitrchisonia beUacinctay Hall. 



29. " mbfimformis. Hall. 



30. " bicmcta, Hall. I 



31. " sp. ? 



32. Bucania punctlfrons? Conrad. 



33. " n. sp. 



34. Gyrtolites ornatus, Conrad. 



35. Oncoceras coustrictum, HalL 



36. " n. sp. 



37. Orthoceras multicameratum? 



38. " lamellosum. 



39. Gonioceras, n. sp. Lower. 



40. Cyrtoceras macro-stomum ? Conrad. 



41. Actinoceras tenuiiilum, HalL Lower. 



42. Cytherina, asp. 



HI. 



Harpeth 



from the last. 



;pect 



Along the southeastern escarpments of the basin, the black 

 slate rests directly upon the layers of " blue limestone'^ contain- 

 ing Spirifer lynx and its associates, (<§. 5.) Passing westward, 

 however, the group under consideration intervenes, and thickens, 

 as is shown by the bluffs of the Harpeth and Duck rivers, as we 

 proceed. Thus, like a great wedge, it separates two groups, 

 which are adjacent on one side of the basin, making them in 

 fact unconformable. Along the Tennessee river the group is 

 well developed. The " Cedar. Glades" oi Perry, Decatur and 

 Hardin counties have become already, by the researches of Dr. 

 Troost, classic ground to the Palasontologist. The group, no 

 doubt, includes rocks both of Upper Silurian and Devonian age. 

 In Sumner county, but a few feet below, the slate Penta7nenis 

 oblon^us may be gathered in abundance, affording evidence Xhat 

 along the northern slopes the strata are mostly Upper Silurian. 



SECO.NJJ Seetcs, Vol. XII, No. 36.— Nov., 1851. 46 



