;V 



. • '• 



On the Silm-ian. Basin of Middle Tennessee. 3o9 



ram, it is frequently encrusted with alum salts and copperas^ due 

 to the decomposition of pyrites. 



In the northern part of the state, it is from forty to sixty feet 

 thick, but thins out almost'-entirely towards the southw^ost; in 

 many places ohen, as along Buffalo river, and in Hardin county, 

 but a k\v inches of it are to be seen, sometimes scarcely a trace 



—a fact expressed upon the map by the broken part of the heavy 

 line. 



I have not been able to discover more than three small shellsj 

 of which but one has been well made out. In addition to the 

 shells it occasionally affords fragments of leaves and wood. A 

 Lingula^ the shell referred to above, has been figured by Owen 

 and Norwood in a pamphlet, entitled, "Researches among the 

 Protozoic and Carboniferous rocks of central Kentucky." They 

 consider it allied to Z . spatula of the Genesee slate, though it is 

 rather broader in prof ^rtion to its length. One of my specimens 

 IS a new species of Cnonetes ; it was obtained, together with the 

 others in Maury county. 



V. Siliceous Group, 



# 



18. This series — the "siliceous stratum" of Dr. Troost — in- 

 cluded between the black slate and the pentremilal limestone, is 

 Well marked throughout by its siliceous characters. 



There appears to be doubt as to the age o( the lowest beds, 

 some regarding them as Devonian, others as carboniferous ; we 

 are inclined to adopt the latter view, and hav^e upon the map re- 

 garded the entire group as carboniferous. The species are cer- 

 tamly closely related to carboniferous types.f 



19, This series has been divided into two members. 



{a.) Siliceous beds,— This member, including in the northern 

 part of the state about 200 feet, appears to have had partly a 

 chemical, and partly a mechanical origin. It consists mostly of 

 a fine-grained, siliceous rock — sometimes approaching a fine 

 sandstone; when freshly quarried, it is of a light blue color, 

 and compact ; it contains but little calcareous matter, and is often 

 interstratified with layers of hornstone or flint ;— occasionally 

 feeds of bluish siliceous shale are met with. Upon exposure, 

 the rock, especially when more than usually calcareous, decom- 

 poses, losing its blue color and becoming a soft, mosi]y yellow, 

 sometimes grayish, sandstone or shale. The Lebanon and 

 Sparta turnpike exposes an entire section at Snow's hill, which 



GW 



and need to be worked out. I trust, however, that the tollowiug notice mude out 

 Kiostly from personal observations mar add something to what was before known 

 <*! these rocks. See, in addition, Troosfs reports. 



f See Researches of Owen and Norwood before referred to. 



