July 10, 1896.] 



SCIENCE. 



39 



Compared with the Appalachian Valley- 

 belt to the east, the structure of this region 

 is simple. Its most striking features are 

 the Sequatchie anticline and fault. On 

 either side the strata are nearly horizontal, 

 forming a broad, shallow syncline on the 

 east, and passing westward with a few low 

 undulations into the great expanse of hori- 

 zontal strata of the Mississippi Basin. 



The most important economic interest in 

 the region is coal. Workable beds occur 

 both in the Lookout and in the "Walden 

 formations. The lower beds, those in the 

 Lookout, are variable in position and thick- 

 ness, so that, while they afibrd much excel- 

 lent fuel in places, they are not generally 

 suitable for working upon a large scale. 

 Their character at Bon Air, where they are 

 extensively developed, is exceptional. The 

 most important coal seam in the region, by 

 reason of its greater thickness and uni- 

 formity, is the Sewanee, which occurs in 

 the Walden sandstone a short distance 

 above the Lookout conglomerates. Its area, 

 within the limits of the Pikeville quarter- 

 degree, is about 500 square miles, of which 

 the greater portion is workable. 



FOLIO 22, MCMINN VILLE, TENNESSEE, 1895, 



This folio, by Charles Willard Hayes, 

 consists of 3 pages of text, a topographic 

 sheet (scale 1:125,000), a sheet of areal 

 geology, another showing the economic 

 geology and another giving structure sec- 

 tions. Following the text is a generalized 

 columnar section for the district, accom- 

 panied by vertical sections showing the 

 position and thickness of coal beds. 



The quarter-degree covered by the Mc- 

 Minnville folio has an area of 980 square 

 miles. It joins the Pikeville and Sewanee 

 quarter-degrees on the east and south. The 

 greater part of its surface is within the 

 highland rim. Its northwestern corner in- 

 cludes a small portion of the central basin 

 of Middle Tennessee, and its southeastern 



corner is occupied by the Cumberland Pla- 

 teau. From northwest to southeast, then, 

 the surface rises by steps from the central 

 basin, with an altitude of 700 feet, to the 

 highland rim, at 1,000 feet, and again to 

 the Cumberland Plateau at 1 ,800 feet. Each 

 step or terrace is part of a more or less 

 perfectly preserved peneplain produced by 

 long-continued erosion, when the land 

 stood relatively lower than now. The pla- 

 teau, which is the highest and consequently 

 the oldest of these plains, formerly ex- 

 tended far to the westward, but has been 

 worn away by the action of streams during 

 and since the formation of the next lower 

 plain. In the same manner the streams 

 are wearing down the second to the level of 

 the third plain, and the escarpment which 

 separates the two is slowly working back- 

 ward toward the southeast, following the 

 retreat of the higher plateau escarpment. 



The McMinnville quarter-degree lies en- 

 tirely beyond the westernmost of the sharp 

 folds Avhich characterize the Appalachian 

 Valley belt. Its strata are nearly horizon- 

 tal, having a very gentle and uniform dip 

 toward the southeast of about 30 feet to 

 the mile. The strata exposed measure 

 only 1,700 feet in thickness, which is but a 

 small fraction of the thickness exposed in 

 regions containing folds. Of these 1,700 

 feet of strata, about 1,500 are Carboniferous, 

 consisting of coal-measure sandstones and 

 shales, forming the upper portion of the 

 plateau, and limestones forming the lower 

 portions of the plateau escarpments and the 

 surface of the highland rim. Beneath the 

 Carboniferous formations are from 10 to 30 

 feet of black shale, which appears to repre- 

 sent the whole of the Devonian deposition 

 in this region. The streams in the north- 

 western corner of the quarter-degree have 

 cut down through the Carboniferous and 

 Devonian, and as much as 200 feet into 

 the underlying Silurian limestone. The 

 upper division of the Silurian on the 



