PRINCIPLES or 8TRATIGRAPHIC CORRELATIONS^ 549 



The so-called Knox of the northeastern part of the valley of east 

 Tennessee, as at Jonesboro and in Tuckaleeche cove, is a totally different 

 formation, being noncherty, less magnesian, altogether younger, and ap- 

 parently wholly referable to the Canadian system. To the south in 

 Alabama another formation about 1,000 feet thick, characterized by 

 abundant, soft mealy chert, and for which the name Chepultepec is 

 elsewhere proposed, is intercalated between the top of the typical Knox 

 and the overlying Canadian limestone and dolomite. Between Pelham 

 and Helena and in the vicinity of Montevallo all three of these forma- 

 tions are present but at Chepultepec, in Blount county, Alabama, the 

 upper is absent, the Chepultepec there being in contact with the 

 Stones River. 



Sections in Alabama add important formations also to the base of the 

 Ozarkian. In the Birmingham Valley some hundreds of feet of very 

 pure dolomite, to which Mr. Charles Butts of the U. S. Geological 

 Survey has applied the name Ketona, underlies the typical Knox. About 

 midway between Birmingham and Montevallo, according to recent 

 investigations by Mr. Butts, another, but highly siliceous, magnesian 

 limestone, attaining a thickness of over 1,000 feet, wedges between the 

 Ketona and the sharply defined top of the underlying thin-bedded upper 

 Cambrian limestone of the Conasauga formation. Not only is a new 

 Ozarkian formation intercalated, but both the overlying Ketona dolomite 

 and the underlying Conasauga limestone are thicker than usual. More- 

 over, a few miles farther south a third, also highly siliceous, magnesian 

 limestone, is intercalated between the top of the Ketona and the base 

 of the typical Knox. This third addition to the lower part of the Ozar- 

 kian is lithologically very similar to the Potosi dolomite of the Missouri 

 section. As the two seem also to agree exactly in stratigrapliic position, 

 the same name might justly be applied in both areas. 



The lesson taught by the Ozarkian in east Tennessee and Alabama is 

 that the break between the Knox and the upper Cambrian in the vicinity 

 of Knoxville is greater" than it seems. In fact, by the time one has reached 

 Montevallo he will have learned that the break represents more than 

 2,500 feet of dolomite. I say more because the break at the top of the 

 Cambrian remains in evidence as far south as the formation can be seen — 

 that is, to the edge of the Cretaceous overlap. Now if this break im- 

 plies, as I have no doubt it does, that sea withdrawal occurred at the close 

 of the Conasauga Cambrian, and as we have no record of intermediate 

 deposits elsewhere in eastern America, it is justly inferred that the result- 

 ing emergence affected the whole of the valley and probably the whole 



