232 INDEX TO THE STEATIGRAPHY OF NORTH AMERICA. 



on the Bays, consists of red and brown calcareous shales, is 400 to 500 feet thick, 

 and carries beds of fossiliferous limestone 4 to 8 feet thick which constitute the 

 fossil iron ores so far as the lime has been replaced by iron/''^ 



The type locality of the "Rockwood" formation is in the Kingston quadrangle, 

 Tennessee. The " Rockwood " is there the only representative of the Silurian, but 

 no unconformity is noted either below it at the contact with the Athens shale or 

 Chickamauga limestone (Ordovician) or above it at the contact with the Chatta- 

 nooga shale (Devonian). Hayes ^^^ states that the "Rockwood" (Clinton) varies 

 widely in character and thickness within the quadrangle. About the head of the 

 Sequatchie Valley "it is 165 feet thick and is composed of calcareous shales inter- 

 bedded with blue limestone." Along the foot of the Cumberland escarpment "it 

 is about 600 feet thick and consists of calcareous and sandy shales. Still farther 

 east * * * the formation attains a thickness of 850 to 1,000 feet, a considerable 

 part of which is coarse sandstone interbedded with sandy shales. Toward the top 

 are sandy shales and a few calcareous beds, with which is associated the iron ore." 



A similar description applies to the "Rockwood" (Clinton) as it occurs in the 

 Chattanooga quadrangle, Tennessee, as far south as latitude 35°. 



I-K 16. INDIANA, OHIO, KENTUCKY, AND TENNESSEE. 



Silm"ian strata envelop the Cincinnati arch and the Nashville dome in the 

 States of Indiana, Ohio, Kentucky, and Tennessee. There is in many places an 

 unconformity at their base corresponding to the latest Ordovician. The strata 

 themselves are very largely limestones, which differ locally in character and in 

 faunal contents. They have been minutely classified, and the details are to be 

 found in the State reports and in recent articles.^^"- ^"' '"- ^*'' ^^^' *^^ 



The Silurian strata of Indiana may be divided, according to Foerste,^*^ into — 



Feet. 



Louisvillfe limestone (at the top) 55+ 



Waldron clay 4-20 



Laurel limestone 40-48 



Osgood clay and limestone 11-16 



Clinton limestone (at the base) 0-11 



The "Clinton" is regarded by Foerste as distinct. The other four divisions 

 he assigns to the Niagara. 



The "Clinton" succeeds the Ordovician with local unconformity and contains 

 rounded fragments of Ordovician rocks around the margins of islands, which it did 

 not cover. It is in niany places a detrital limestone but has also dense siliceous or 

 clayey facies. 



The Osgood consists chiefly of clay shale with 8 to 15 inches of limestone at 

 the base. Where the shale gives place to lime the limestone thickens, and it is 

 correlated with the Dayton limestone of Ohio. 



The Laurel limestone is usually hard, white, and evenly bedded. Toward the 

 south it becomes softer and more argillaceous. 



The Waldron shale is a distinct bed overlying the Laurel, and is mainly a clayey 

 shale having the facies of the Osgood shale. It becomes calcareous toward the 

 north. 



