Geology. 



181 



Its greatest development is perhaps in Clinch Mountain. In southern 

 East Tennessee, it is unimportant, and rarely seen. 



2. Shales, thin fine Sandstone, and Iron Ore. — This member, two or 

 three hundred feet thick at some points, is composed of variegated 

 shales, often calcareous, and including thin layers of brown and gray 

 fine sandstones, often beautifully ripple-marked. 



The dyestone is imbedded in the shales, and generally occurs in one 

 or two layers, etc. All these strata contain organic remains. 



3. Sneedville Limestone. — At Sneedville, and several other points in Han- 

 cock and Claiborne, a band of gray limestone, which perhaps will be 

 found to be from one to two hundred feet in thickness, rests upon the 

 last member. It occasionally affords interesting beds of fossil corals. 

 In Middle and West Tennessee, this formation is almost wholly gray, 



or bluish-gray, limestone. Some of its strata are blue, others reddish, 

 and many of them argillaceous. 



It is wanting along the eastern slope of the Central Basin, but appears 

 again along its western and northwestern sides. It is here generally less 

 than fifty feet in thickness, though sometimes more. Going westward, it 

 thickens rapidly, and, becoming several hundred feet thick in Hardin, 

 Decatur, etc., occupies the valley of the Tennessee in those counties. 



Its lowest member is the hydraulic limestone of which we have spoken. 

 It affords, too, the marble of Henry, Benton, etc. 



Lower Silurian. — (5.) Central Limestone and Shale Group. — 5. 

 Calcareous shales of Bay's Mountain, etc. ; 4. Red sandy limestone of the 

 Knobs in Monroe, McMinn, etc. ; 3. Beds of variegated and gray marble 

 in Hawkins, Knox, etc.; 2. Blue shelly-limestone of many valleys in 

 East Tennessee; 1. Blue limestone of the Central Basin, Middle Tennes- 

 see ; corresponding in order to the Hudson River group, Trenton lime- 

 stone, Black River limestone. 



The entire area within the Central Basin of Middle Tennessee is oc- 

 cupied by nearly horizontal strata of blue limestones, in all, perhaps, from 

 800 to 900 feet in thickness, which belong to this formation. 



They are easily divided into two nearly equal members, which we have 

 called, respectively, commencing with the lower, the Stones River and 

 Nashville sub-groups. 



1. The Stones River, or lower member, is a series of blue and dove-col- 

 ored limestones, more or less cherty, not generally as argillaceous as 

 those of the succeeding member, and often remaining thick-bedded 

 when weathered ; it contains, however, several thin-bedded argillaceous 

 divisions. 



2. The Nashville Member is blue argillaceous, more or less sandy, com- 

 pact, and highly fossiliferous limestone, weathering, generally, into 

 thin-bedded rough layers, often separated by seams of shaly matter. 



The marble of Franklin is a local stratum in the topmost part of 

 this member. 



These two sub-groups are distinctly separated by fossiliferous charac- 

 ters. The first is equivalent, generally, to the Black River groups and 

 lower Trenton, and the second to the Hudson River group, Utica slate, 

 and upper Trenton, of New York. 



