MayI, 1896.] 



SCIENCE. 



65491 



of the Cumberland Plateau. The surface 

 of this half, except in the Crab Orchard 

 mountains, is comparatively level and has 

 an altitude of between 1,800 and 1,900 feet. 

 Its streams flow in shallow channels until 

 near the edge of the plateau, when they 

 plunge into rocky gorges which form deep 

 notches in the escarpment. The Crab 

 Orchard mountains are formed by the un- 

 eroded portions of an anticline, the hard 

 beds rising in the form of a low arch. 

 Toward the southwest the hard beds were 

 lifted higher and have been removed, ex- 

 posing the easily erodible limestone beneath, 

 and in this the Sequatchie Valley has been 

 excavated. The southeastern half of the 

 district lies within the great Appalachian 

 Valley, here occupied by the Tennessee 

 river, which flows at an altitude of about 

 700 feet, and above which rounded hills and 

 ridges rise from 300 to 500 feet higher. 

 The valley ridges have a uniform northeast- 

 southwest trend parallel with the Cumber- 

 land escarpment, their location depending 

 on outcrop of narrow belts of hard rocks. 



Geology. — West of the Cumberland es- 

 carpment the geologic structure is very sim- 

 ple. The strata remain nearly horizontal, 

 as they were originally deposited, except in 

 the Crab Orchard mountains, where they 

 bend upward, forming a low arch. East of 

 the escarpment the strata have sufifered in- 

 tense compression, which has forced them 

 into a great number of narrow folds whose 

 axes extend northeast and southwest. The 

 strata dip more steeply on one side of the 

 arch than on the other ; and, as a further 

 effect of compression, the beds on the 

 steeper (generally the northwestern) side 

 have been fractured and the rocks on one 

 side thrust upward and across the broken 

 edges of those on the other. In this man- 

 ner the folds first formed have in most 

 cases been obliterated, and there remain 

 narrow strips of strata separated by faults, 

 and all dipping to the southeast. 



The rocks appearing at the surface are 

 entirely sedimentary — limestones, shales, 

 sandstones and conglomerates — and include 

 representatives of all the Paleozoic groups. 

 The Cambrian formations consist of the 

 Apison shale, Rome sandstone and Cona- 

 sauga shale, a series which is calcareous at 

 top and bottom and siliceous in the middle. 

 The Conasauga passes upward through blue 

 shaly limestone into the Knox dolomite, a 

 formation about 4,000 feet in thickness, 

 composed of siliceous or cherty magnesian 

 limestone. Probably the lower portion is 

 of Cambrian age, while the upper is un- 

 doubtedly Silurian. Above the dolomite is 

 the Chickamauga limestone, whose upper 

 portion toward the eastern side of the dis- 

 trict changes from blue flaggy limestone to 

 calcareoiis shale, and is called the Athens 

 shale. The next formation is the Eock- 

 wood, which also changes toward the east 

 from calcareous shale to hard, brown sand- 

 stone. These changes in the character of 

 the rocks indicate that, while they were 

 forming, the land from which their mate- 

 rials were derived lay to the southeast. 

 The Devonian is represented in this region 

 by a single stratum of carbonaceous shale, 

 the Chattanooga black shale, which rests, 

 probably with a slight unconformity, on the 

 Rockwood. Above the Chattanooga are 

 the Fort Payne chert and Bangor limestone 

 of the lower Carboniferous, and the Look- 

 out and Walden sandstones of the Coal 

 Measures. 



Mineral resources. — These consist of coal, 

 iron ore, limestone, building stone and clay. 

 The coal-bearing formations, the Walden 

 and Lookout, form the surface of the greater 

 part of the district northwest of the Cum- 

 berland escarpment, making a probably 

 productive area of 370 square miles. The 

 Lookout always contains one, and some- 

 times as many as four, beds, all of which 

 are locally though not generally workable. 

 The upper bed, immediately below the con- 



