146 THE CAMBRIAN. Iiht.l.81. 



group ; first by about 2,400 feet of shales, and then by 5,000 feet of 

 cherty limestones 1 . Combining these estimates we have .8,000 feet of 

 Primordial and 2,400 feet of shales .corresponding in position to the 

 Knox shales, which gives a total of 10,400 feet for the Cambrian rocks 

 of Georgia, as estimated. This paper is accompanied by a section 

 crossiug Dade, Walker, and Gordon Counties in northwestern Georgia. 

 The stratigraphic relations of the Cambrian rocks are *shown as they 

 occur in Gordon County. 



A geological section of the Cambrian rocks of northwestern Georgia 

 has recently been published by Mr. C. Willard Hayes of the U. S. 

 Geological Survey. It is referred to in the description of the Cambrian 

 rocks of Georgia. 2 



ALABAMA. 



The report of Prof. M. Tuomey for 1858 3 contains a very general 

 description of the formations of the State, and on the accompanying 

 map the Silurian and Devonian formations are included under one 

 color, so that it is impossible to differentiate that portion of the Silu- 

 rian formation which has subsequently been found to belong to the 

 Cambrian group. In a general north and south section, showing the 

 disposition of the strata, the Silurian and Devonian rocks are repre- 

 sented as unconformably subjacent to the Coal Measures and mountain 

 limestone. 



A long interval elapsed between the work of Prof. Tuomey and the 

 organization of the geological survey under Prof. Eugene A. Smith. 

 In the report of progress of the latter, for the year 1875, a general 

 description of the geological formations of Bibb, Shelby, Talladega, 

 and Calhoun Counties is given. In this area there is a large develop- 

 ment of metamorphic rocks described by Prof. Smith in the report for 

 1874. 4 Of this series he says : 



On the southeastern border of the Silurian formation in Alabama, from the Georgia 

 line to the northeast corner of Chilton County, a stratum of crystalline limestone, 

 almost pure carbonate of lime, may be traced by its occasional exposures. * * * 

 Succeeding this limestone and apparently overlying it conformably * * * is a 

 series of semi-metamorphio strata between 15,000 and 20,000 feet in thickness, strik- 

 ing northeast and southwest and dipping at high angles (45°) southeast. This series, 

 beginning below, is composed of greenish gray hydro-mica slates (talcoid slates, nac- 

 reous argillites, talcose slates), passing upwards into a conglomerate by enclosing 

 lumps of quartz; these slates are succeeded by thick beds of quartzite, alternating 

 with greenish chloritic schists. The quartzite in places is a thin-bedded silicioue 

 slate, again a thick-bedded quartzose conglomerate, and still again a laminated 

 quartzose or arenaceous rock, not very coherent, and enclosing small grains of quartz. 



1 Northwest Georgia. (Geologic description.) Tenth Census U. S., vol. 6; Report on Cotton Pro- 

 duction in the United States, Part 2, 1884, p. 287. 



2 The overthrnst faults of the southern Appalachians. Bull. Geol. Soc. America. Vol. 2, Feb., 1891, 

 p. 143, pi. 3- 



8 Second biennial report on the geology of Alabama. Montgomery, 1858, pp. 168. 

 4 Geological survey of Alabama. Report of progress for 1874. Montgomery, Alabama, 1875, pp. 

 21-25. 



