304 



THE CAMBRIAN. 



[BULL. 81. 



As noticed in the historical review, Mr. McCutchen's estimates of the 

 thickness of the formations referred to the Primordial is 8,000 feet, and 

 to the Knox shale series 2,400 feet, makiDg a total thickness of 10,400 

 feet. The estimates of the author we have just quoted assign to the 

 Knox shale a thickness of 3,500 feet, which will give a still greater 

 thickness for the total Cambrian section. I think, however, that all 

 such estimates must be carefully revised, as the rocks of the Knox 

 shale series are very much disturbed by plications and faulting. 



An unpublished section, by C. Willard Hayes, of the Appalachian Di- 

 vision of the U. S. Geological Survey, extending from Rome, Georgia, 

 to Gadsden, Alabama, gives the following series, extending from the 

 top downward : 



Silurian. 



2 



s 



OS 



o 



93 



cS 

 fcfi 

 ri 



c3 



GO 



e3 



a 







© 



8*2 



2 o 



© 



I 



l-t ' 

 cS 



c3 

 cS 



GO 



o 

 o 

 O 



Knox dolomite 



Thin bedded seamy limestone, sometimes blue and mass- 

 ive. 



Yellow shales, calcareous, grading into seamy limestone. 



Earthy limestone interbedded with shales, often want- 

 ing ; locally carries nodules of chert. 



Yellow shales. 



Oolitic limestone; thin beds in light green or yellow 

 shales. 



Variegated sandy shales, purple, green, brown, etc .... 



Thin beds of highly colored sandstone : red, purple, and 

 green ; show ripple marks and sun cracks. Beds 1 

 to 12 inches thick with interbedded shales. Maxi- 

 mum thickness shown between Eorae, Georgia, and 

 Big Cedar Creek 



Green shales, with thin, hard, siliceous beds, \ to 2 

 inches thick, or layers of flat nodules. Maximum 

 thickness at Georgia-Alabama line 



Fine yellow or brown shales, containing some beds of 

 blue limestone 



Heavy beds blue, seamy limestone 



Yellow or green clay shales, with thin beds of blue 

 limestone contorted and filled with calcite veins. 

 Sometimes the shales contain siliceous nodules. Al- 

 ways highly contorted. Cover a large area between 

 Rome and Gadsden, and form the " Flatwoods" of 

 Coosa Valley. Thickness not known; probably not 

 less than 



Feet. 

 4,000-5,000. 



1,600-2,000 



1,300-1,800 



700-1,500 



1,0004- 

 600i 



3,500 



In a recent paper on the valley rocks of northwestern Georgia, Mr. 

 Hayes assigns a thickness of 1,600 to 2,000 feet to the Connasauga 

 (= Monte vallo of Smith) shales; 2,000 to 3,500 feet to the Kome sand- 

 stone and Weisner quartzite, and 3,000 feet plus to the Coosa shales. 1 



In a section at Mount Weisner, Alabama, Mr. Hayes found a quartz- 

 ite that he considers to correspond to the Eome sandstone. It has a 

 thickness of about 800 feet, and is in the form of lenticular masses of 

 white quartzite; sandstone and conglomerate occur at the base and 



1 The Overthrust faults of the southern Appalachians. Bull. Geol. Soc, America, vol. 2, Feb., 1891, 

 p. 143, pi. 3. 



