CLASSIFICATION OF GEOLOGICAL FORMATIONS OF TENNESSEE 13 



interbedded. Thin layers of the phosphate rock are seen at points interlaminated 

 in the lower part of the Black shale.* 



In the "Swan Creek phosphate " we have another recently recognized member 

 of the Tennessee geological column, and an interesting and important one. Its 

 horizon is always indicated by the Black shale above and often by the Hardin 

 sandstone below. It is the third phosphate rock.| 



The "Maury Green shale" has importance as holding imbedded in it ball and 

 kidney shaped concretions of phosphate rock. The concretions contain from 50 to 

 60 per cent of calcium phosphate. The shale has a thickness of from a few inches 

 to 5 feet. The concretions make a, fourth horizon of phosphate. 



In the vicinity of Tullahoma, in the breaks of the flat highland on which Tulla- 

 homa is located, are beautiful waterfalls or cascades, J where may be seen good sec- 

 tions of a characteristic cherty limestone belonging to this division. Hence the 

 name "Tullahoma limestone " was adopted. The same rock is seen in the bed of 

 the stream at the edge of the town. At other points it has been thoroughly leached, 

 the calcareous part being removed and layers or blocks of chert or shale left. 



As a whole, the lower part of the sub-Carboniferous in Tennessee is markedly 

 silicious. In the west we have a calcareo-silicious shale w 7 ith chert (the Harpeth 

 shale) ; then cherty limestone, leaving by weathering, masses of chert ; and finally 

 in the east sandstones and shales. These sandstones and shales have recently been 

 referred to the Devonian under the name of the Grainger shale, but there is good 

 reason for believing them to be sub-Carbonferous where they were originally 

 placed.^ 



The name " Mountain limestone " for Tennessee and north Alabama is especially 

 appropriate. It is the great formation of the base of the Cumberland mountains. 

 Hence we have retained it. 



The subdivisions of the Coal Measures given— the " Bon Air," the " Tracy. City," 

 and the " Brushy Mountain " — are in good part topographical and are intended for 

 Tennessee students. Though an expedient, there is reason for this arrangement. 

 The Cumberland mountains, speaking generally, are a great tableland. The fiat 

 rock of large areas of this tableland is the great conglomerate, recognized as such 

 from Pennsylvania to Alabama, and which for local reasons I have named Sewanee 

 conglomerate. This rock terminates .the Bon Air measures above. Important 

 coal beds and mines lie below it ; among them the Bon Air mines ; hence the 

 name of the division. 



Above this, terrace-like, rises the second division. It makes many second 

 benches and upper, back smaller tables. This is likewise terminated above by a 

 conglomerate. The division is from 250 to 500 feet thick and contains from three 

 to five seams of coal, the most important of which, the name Sewanee, is exten- 

 sively mined in the vicinity of Tracy City, the town giving name to the division. 



* It has been suggested that the Black shale is Mississippian (sub-Carboniferous) ; if so, then the 

 Hardin sandstone and the Swan phosphate are most likely of the same age. 



fSee, further, Elements, p. 138 ; also the American Geologist, vol. xii, 1894, pp. 107-110, and other 

 published accounts. In the Geologist a section is given embracing the formations above and 

 below. 



X At the base of the sections of the cascades may usually be seen the Maury Green shale, the 

 Black shale, and the Swan Phosphate, all however, thin and poorly represented, especially the 

 Green shale and the Phosphate. 



I Geology of Tennessee, Nashville, 1869, pp. 298-348. 



