236 EEPOET OF NATIONAL MUSEUM, 1899. 



residual material consists mainly of ferruginous clay with large 

 amounts of chert, and reaches a thickness of 100 feet or more. The 

 bauxite deposits in the Rock Run district are regarded as typical for 

 the entire region, and are described as follows: 



Four bodies of the ore were being worked in 1893 on a considerable scale, and all 

 show practically the same form. The southernmost' of the four, called the Taylor 

 bank, is located 3h miles northeast of Rock Run, near the western base of Indian 

 Mountain. Although the heavy mantle of residual material effectually conceals the 

 underlying rocks, the ore appears to be exactly upon the faulted contact between the 

 narrow belt of Knox dolomite on the northwest and the sandy shales and quartzites 

 of Indian Mountain on the southeast. The ore is covered by 3 or 4 feet of red sandy 

 clay in which numerous fragments of quartzite are imbedded. The ore-body is an 

 irregularly oval mass, about 40 by 80 feet in size. Its contact with the surrounding 

 residual clay, wherever it could be observed, appeared to be sharp and distinct, and, 

 about the greater portion of its circumference, very nearly vertical. A certain amount 

 of bedding is observable in the ore-body, although no trace of bedding can be detected 

 in the surrounding residual material. Upon the northwestern or down-hill side of 

 the ore-body, this bedding is very distinct. Layers of differently colored and differ- 

 ently textured ore alternate in regular beds, a few inches in thickness, and above 

 these are thinner beds of chocolate and red material, probably containing consider- 



v:-:;i-^w>(i:te'.;---..-., 



° °°° "■ BOTTOM OF P IT . ._ N"^ .^ ■, , ^ ■""'^'"'■"eci.CUy 



\ ' 'DRAINAGE DIT CH ^>^"-- 



Fig. 7. 



SECTION SHOWING RELATION OF BAUXITE TO MANTLE OF RESIDUAL CLAY IN GEORGIA. 



After C. W. Hayes. 



able kaolin. These beds have a steep dip, somewhat greater than the slope of the 

 hill-side, but in the same direction. They are not simply inclined planes, however, 

 but are curved, so as to form a steeply-pitching trough. With increasing distance 

 from the ore-body, the lamination becomes less distinct, and the beds pass gradually 

 into a homogeneous mottled clay. The accompanying section, tig. 7, shows these 

 relations of the ore and residual mantle. 



At the Dike bank [see Fig. 6], about a mile northeast of the one above described, 

 the stratification is well shown in portions of the deposit. Beds of yellow and gray, 

 tiiTe-grained material, alternate with others of pisolitic ore. The beds dip at an angle 

 of about 40°, and are curved so as to form a steep trough. The compact material 

 also shows distinct cross-bedding; both primary and secondary planes dipping in 

 the same direction. 



In the Gain's Hill bank, about 250 yards north of the Dike bank, the ore-body 

 shows a more regularly oval form than in most of the other deposits, and is also 

 somewhat dome-shaped, swelling out laterally from the surface downward, as far as 

 the working has progressed. 



Although some of the workings have gone to a considerable depth (in a few cases 

 50 feet or more), the bottom of the ore-body has not been reached in any case. 

 The ore varies in composition with depth, but not in a uniform manner, nor more 

 than do different portions at the same depth. The deepest pits have not gone 

 below the base of the surrounding residual mantle, so that no observations have yet 



