ABSTRACTS 76 1 



the eastern third of the district, while a broad undulating valley occu- 

 pies its central portion. The latter is drained in part northward by- 

 tributaries of the Tennessee and in part southward by streams flowing 

 directly to the Gulf. The divide separating the two drainage systems 

 is broad and low, and there is evidence that the Tennessee River 

 formerly flowed southward across the divide. 



Geology — The rocks appearing at the surface within the Ringgold 

 district are entirely of sedimentary origin, and include representatives 

 of all the Palaeozoic groups. The oldest rocks exposed are shales, sand- 

 stones, and thin-bedded limestones of Lower and Middle Cambrian age. 

 These are called the Apison shale, Rome sandstone, and Conasauga 

 shale. Above these formations is a great thickness of siliceous mag- 

 nesium limestone, the Knox dolomite, the lower portion probably 

 being Cambrian and the upper portion Silurian. The remaining Sil- 

 urian formations are the Chickamauga limestone and the Rockwood 

 sandstone. The Devonian is either wholly wanting or is represented 

 by a single thin bed of carbonaceous shale, not over 35 feet in thick- 

 ness. Above the Chattanooga black shale are the Fort Payne chert, 

 Floyd shale, and Bangor limestone forming the Lower Carboniferous, 

 and the Lookout and Walden sandstones forming the Coal Measures. 

 Most of the formations thicken eastward, and at the same time the pro- 

 portion of calcareous matter decreases, showing that the land from 

 which the materials composing the rocks were derived lay to the east. 



The region has been subjected to compression in a northwest-south- 

 east direction, and the originally horizontal strata would have been 

 thrown into a series of long, narrow folds whose axes extend at right 

 angles to the direction of the compression, or northeast and southwest, 

 The effects of compression were greatest in the eastern portion of the 

 district, where the strata are now all steeply inclined and the basal 

 beds form sharp ridges, while in the western portion considerable areas 

 of strata remain nearly horizontal and form plateaus. Where the fold- 

 ing was greatest there was also much fracturing of the rocks, and the 

 strata on the eastern side of a fracture are in many places thrust upward 

 and across the broken edges of the corresponding strata on the west. 

 Most of the ridges in the district have thrust faults of this character 

 along their eastern basis. 



Mineral Resources. — These consist of coal, iron ore, mineral paint, 

 manganese ore, limestone, building stone, and brick and tile clay. 

 The productive coal-bearing formations, the Lookout and Walden 



