GENERAL OBSERVATIONS. 379 



fifth, of Illinois and Missouri, which are near its centre, — the former by A. H. 

 Worthen, the latter by G. C. Swallow, but with changes from more recent 

 information ; the sixth, of Tennessee, the eastern part of which is in the Appa- 

 lachian region, and the middle and western in the Interior, by J. M. Safford. 

 In each case the sections begin below. 



1. Pennsylvania Section. 



Lower Silurian. 



Potsdam, Potsdam Epoch. — "Primal Series" of Kogers, — Sandstones and 

 Slates, 3000-4000 feet. 

 Calciferous Epoch. — "Auroral" Calcareous Sandstone, 250 feet. 

 Trenton, Chazy Epoch. — "Auroral" Magnesian Limestone, with some cherty 

 beds, 5400 feet. 

 Trenton Epoch. — " Matinal" Limestone with blue shale, 550 feet. 

 Hudson, Utica Epoch. — "Matinal" bituminous slate, 400 feet. 



Hudson Epoch. — " Matinal" blue shale and slate, with some thin gray 

 calcareous sandstones, 1200 feet. 



Upper Silurian. 



Niagara, Oneida Epoch. — "Levant Gray" Sandstone and Conglomerate, 700 



feet. 

 Medina Epoch. — "Levant Red" Sandstone and Shale, 1050 feet; and 



" Levant White" Sandstone, with olive and green shales, 760 feet: 



total, 1810 feet. 

 Clinton Epoch. — " Surgent Series," Shales of various colors, both argil- 

 laceous and calcareous, with some limestones, ferruginous sandstones, 



and iron-ore beds, 2600 feet. 

 Niagara Epoch. — Not well defined; possibly corresponds to part of the 



" Surgent" Series. 

 Salina, Saliferous Epoch. — " Scalent" Variegated marls and shales, some layers 



of argillaceous limestone, 1650 feet. 

 Lower Helderberg. — "Scalent" Limestone, thin-bedded, with much chert, 



350 feet; "Pre -meridian" encrinal and coralline limestone, 250 feet: 



total, 600 feet. 



Devonian. 



Oriskany, Orislcany Epoch. — " Meridian" calcareous shales, and calcareous and 



argillaceous sandstone, 520 feet. 

 Corniferous, Cauda -Galli Epoch. — "Post-meridian" silico-calcareous shales, 

 200-300 feet. 

 Upper Helderberg Epoch. — " Post-meridian" massive blue limestone, 

 80 feet. 

 Hamilton, Marcellns Epoch. — "Cadent" Lower black and ash-colored slate, with 

 some argillaceous limestone, 800 feet. 

 Hamilton Epoch. — " Cadent" argillaceous and calcareous shales and 



sandstone, 1100 feet. 

 Genesee Epoch. — "Cadent" Upper black calcareous slate, 700 feet. 



