650 



SCIENCE. 



[N. S. Vol. III. No. 70. 



glomerate, is the most constant. The greater 

 part of the workable coal is contained in 

 the Walden, the lower bed probably cor- 

 responding to the Sewanee seam farther 

 west. This occurs in a belt 6 or 8 miles in 

 width, along the eastern edge of the plateau. 

 The only iron ore sufficiently adundant to 

 be commercially important is the red fossil 

 ore, which occurs as a regularly stratified 

 bed in the Eockwood formation. The 

 numerous folds east of the escarpment 

 bring the Eockwood to the surface in long, 

 narrow bands, along which the ore has 

 been worked at many points. It varies in 

 thickness from 3 to 7 feet, and, although at 

 some places it passes into a sandy shale, it 

 is generally a high-grade ore. 



FOLIO 6, CHATTANOOGA, TENN., 1894. 



This folio consists of 3 pages of text, 

 signed by C. Willard Hayes, geologist ; a 

 topographic sheet (scale 1 : 125,000), a sheet 

 of areal geology, one of economic geology, 

 one of structure sections, and one giving 

 columnar sections. 



Geography. — The map is bounded by the 

 parallels 35° and 35° 30' and the meridians 

 85° and 85° 30'. The district is wholly 

 within the State of Tennessee, embracing 

 portions of Bledsoe, Ehea, Sequatchie, Mar- 

 ion, Hamilton and James counties. It 

 lies partly in the great Appalachian Valley 

 and partly in the plateau division of the 

 Appalachian province. Its surface is marked 

 by two distinct types of topography, the 

 plateau and the valley. The former pre- 

 vails in the western half of the district, 

 which is occupied by portions of the Cum- 

 berland Plateau and Walden Eidge, the 

 two plateaus being separated by Sequatchie 

 Valley. The Cumberland Plateau has an 

 altitude of about 2,100 feet, with a level or 

 rolling surface. Walden Eidge has an alti- 

 tude of 2,200 feet along its western edge, 

 and slopes gradually eastward down to 1,700 

 feet. Both plateaus are bounded by ab- 



rupt escarpments from 900 to 1,400 feet in 

 height, the upper portions being generally 

 formed by a series of cliffs. The two pla- 

 teaus are separated by Sequatchie Valley, 

 which is about 4 miles in width. Its west- 

 ern side, the escarpment of Cumberland 

 Plateau, is notched by numerous deep rocky 

 gorges, cut backward into the plateau by 

 streams flowing from its siirface ; while the 

 eastern side, the Walden escarpment, forms 

 an unbroken wall. The eastern half of the 

 district is occupied by the Tennessee Val- 

 ley, the river itself having an altitude of 

 between 600 aud 700 feet, while rounded 

 hills and irregular ridges rise several hun- 

 dred feet higher. Leaving the broad val- 

 ley, which continues southward into Ala- 

 bama, the Tennessee Eiver turns abruptly 

 westward at Chattanooga and enters a nar- 

 row gorge through Walden Eidge. This 

 part of its channel is very young in 

 comparison with the valley toward the 

 north, and there is evidence that the river 

 has occupied its present course but a short 

 time, having formerly flowed southward 

 directly to the Gulf. 



Geology. — The rocks appearing at the sur- 

 face within the limits of the map are en- 

 tirely of sedimentary origin, and include 

 representatives of all the Paleozoic groups. 

 The Cambrian formations include the Api- 

 son shale, Eome sandstone and Conasauga 

 shale, a series which is calcareous at top 

 and bottom and siliceous in the middle. 

 The Conasauga passes upward through blue 

 limestone into the Knox dolomite — a great 

 thickness of siliceous magnesian limestone, 

 the lower portion of which is probably Cam- 

 brian. Above the dolomite are Chicka- 

 mauga limestone and Eockwood shale, the 

 latter becoming brown sandstone in White 

 Ash Mountain. The whole of the deposi- 

 tion which took place in this region during 

 the Devonian is apparently represented by 

 a stratum of shale from 10 to 25 feet in thick- 

 ness — the Chattanooga black shale, which 



