84 INDEX TO THE STKATIGEAPHY OF NORTH AMERICA. 



from the lower, is the more persistent and is readily distinguished lithologicaUy, being composed 

 of interbedded thin glauconite limestones and thin layers of greenish shale, together making up 

 a thickness of about 80 feet. Some of the limestone layers in the upper half are conglomeratic 

 and many of those in the lower half are filled with fossils. This upper member is an easily 

 recognized and widely distributed division. 



A basal sandstone, overlain by a thin-bedded limestone carrying glauconite and containing 

 the same fauna as that found in this upper member of the Reagan sandstone, occurs at the base 

 of the eo-Paleozoic column in the Llano and Burnet quadrangles, in central Texas. Very 

 similar, apparently contemporaneous deposits and faunas are found also in New Mexico, Arizona, 

 and the Bighorn Mountains of Wyoming. Further, the same fauna, though the rocks depart 

 somewhat lithologicaUy, is yet easily recognized in the Lamotte sandstone and Bonneterre 

 hmestone, perhaps also in the Elvins formation of the Ozark uplift and in the "St. Croix group" 

 of the upper Mississippi Valley. 



I 16. ALABAMA AND GEOBGIA.a 



The Cambrian of the southern Appalachian Valley region is represented by 

 the Weisner quartzite, Beaver limestone, and Rome formation, by the Conasauga 

 shale, and by part of the Knox dolomite. The upper part of the latter is of Lower 

 Ordovician age. Hayes *^^^ described these formations as follows : 



The Weisner quartzite includes the oldest rocks that come to the surface within the limits 

 of the Rome quadrangle. It is confined to the extreme southwest corner; and since it contains 

 the most resistant rocks, the areas of its outcrop are marked by the greatest elevation within 

 the quadrangle — that is, Indian Mountain. The most prominent member of the formation is a 

 hard, vitreous quartzite, but it contains also conglomerates, sandstones, and sandy shales. The 

 coarser elements of the formation constitute a series of lenses, variable in extent and thickness, 

 which are interbedded with the fii^er-grained rocks. The latter make up the bulk of the forma- 

 tion, although they are much less prominent than the more resistant coarser beds. The quartzite 

 when exposed to atmospheric agencies breaks up into angular blocks, which nearly everywhere 

 cover the surface, and exposures of the beds in place are rarely seen. For this reason, ^nd also 

 because of the enormous faults which intersect the formation, its thickness is difficult to deter- 

 mine. On a section from Bluffton to Rockrun its apparent thickness is over 10,000 feet, but it 

 is by no means certain that this apparent thickness is not due in some measure to repetition by 

 faulting and the minute folding of the less resistant beds. The section is limited by a fault on 

 the west, and the foundation upon which the formation was originally deposited is nowhere 

 exposed. Some of the conglomerate beds contain numerous feldspar pebbles, showing that the 

 material composing the conglomerate was derived, in part at least, from granites. It probably 

 came from a source to the southeast, and the beds which form Indian IMountain have the 

 appearance of massive delta deposits. No fossils have as yet been found in these beds, but their 

 relations to adjacent formations are such that there is httle hesitation in correlating them with 

 the lower Cambrian. 



The beds of the Weisner quartzite generally dip to the southeast and, where not limited 

 by a fault, pass under a narrow belt of red clay soil containing many angular fragments of 

 quartzite and a few masses of cellular chert. This red soil is derived from the decay of the 

 Beaver limestone, which is itself rarely seen. It is a gray, semicrystaUine, dolomitic limestone, 

 generally massive, but sometimes slightly shaly. The exposures of this limestone are so infre- 

 quent that its tliickness can not be determined, but, judging from the width of its outcrop and 

 the prevailing dip of the adjoining beds, it is probably between 800 and 1,200 feet thick. The 

 principal areas of the Beaver limestone are in the vicinity of Indian Mountain, but a small 

 area is found at a considerable distance from any outcrop of the quartzite, a few miles south- 

 west of Rome. 



a See also I-J 16-17, Tennessee and North Carolina (pp. 89-98). 



