walcott.] SUMMARY — ALABAMA. 305 



replace a portion of the Rome sandstone. In Indian Mountain it is 

 much thicker than in Mount Weisner, and consists of several beds of 

 quartzite, with intervening masses of yellow sandy shales. 



The fossils collected from the Coosa shales by Dr. Cooper Curtice 

 indicate, as studied by me, the Middle Cambrian fauna of the northern 

 Appalachian section. The Connasauga shale is correlated by its strati- 

 graphic position with the Knox or Upper Cambrian shales of the Ten- 

 nessee section. In Mr. Hayes' table the Rome sandstone and Weisner 

 quartzite are placed on the same horizon with the Knox sandstone, 

 Potsdam or Chilhowee of Smith and Saiford. That the correlation by 

 Messrs. Smith and Saiford of the Weisner quartzite with the Chilhowee 

 is probably incorrect is supported by the fact that the fauna of the 

 Coosa shales belongs above the Chilhowee sandstone in sections where 

 the succession is undisturbed. The Chilhowee sandstone fauna is the 

 type of the Lower Cambrian, and the Coosa shale fauna is that of the 

 Middle Cambrian. 



When the maps of the Paleozoic region of Georgia and Alabama are 

 published geologists will have the data for the geographic distribution 

 of the Cambrian rocks, and also sections showiug the relative position, 

 thickness, and the variations in the character of sedimentation from 

 the south to the north as the formations pass to the north into Ten- 

 nessee. 



ALABAMA. 



Our knowledge of the Cambrian rocks of Alabama is largely obtained 

 from the Report of Progress for L875. The nomenclature adopted for 

 the fossiliferous sedimentary rocks up to the base of the Knox dolomite, 

 by Prof. Saiford, in Tennessee, is followed by Prof. E. A. Smith in this 

 report. To the Primordial or Cambrian series he assigns the Acadian 

 epoch, or the conglomerates and slates corresponding to the typical 

 Ocoee section in Tennessee. To the Potsdam epoch he confines the 

 Chilhowee sandstone of the Tennessee section. The Knox saudstone 

 aud Knox shales are referred to the Canadian period. The term " Cal- 

 ciferous sandstone" is used as the equivalent of Knox sandstone, and 

 i\ Quebec shales " of the Knox shales. The section of the Acadian slates 

 and conglomerates in Talladega County is considered by Prof. Smith 

 typical of this series in Alabama. 1 The description is as follows : 



The western border of the Metamorphic rocks in Alabama is formed by a belt of 

 slates and conglomerates, semi-metamorphic in aspect, and of varying width, but per- 

 haps of an average width of six miles. These rocks, which in every respect seem to 

 be the exact equivalents of Prof. Safford's Ocoee Slates and Conglomerates, are re- 

 ferred like them to the Acadian epoch. 2 



The stratigraphic succession of the beds is not well determined. 

 There is a belt of greenish talcoid, or hydro-mica slate, and a series of 

 conglomerates which are sometimes a slaty, arenaceous rock, but often 



1 Report of Progress of the Geological Survey of Alabama for 1875. Montgomery, 1876, pp. 13-17. 

 •Op. oil., p. 127. 



Bull. 81 20 



