STKATIGKAPHICAL GEOLOGY. 15 



change in lithological character, and is hardly determinable from an examination 

 of the fossils. The lower 2,000 feet is classed with the Helderberg Group in the 

 Silurian, but it may include the Oriskany sandstone of the Devonian series. The 

 upper 7,036 feet are supposed to represent all the other Groups in the Devonian 

 formation of New York, but the divisions are not clearly defined as in New York, 

 nor readily separable from an examination of either the fossils or the rocks. 

 (Geo. of Canada, 1863, p. 396; do. 1866, p. 260; Hall's Pal, vol. iii., p. 45.) 



A very interesting Group of rocks, because of the highly fossiliferous charac- 

 ter and abundance of Goniatites, is exposed at Eockford, near Sej'mour, Indiana, 

 which probably represents part of the Chemung Group; though Prof Meek and 

 the Illinois geologists have regarded it as the representative of the Kinderhook 

 Group. 



The shales and sandstones of the Catskill Group form in their greatest ex- 

 pansion at the Catskill Mountains, from which the Group takes its name, a mass 

 of at least 3,000 feet in thickness. The Group is composed of red and greenish 

 or olive shales and shalj' sandstones, with some graj' and mottled sandstones 

 and conglomerates. 



In Pennsylvania this Group is divided into: 1st, Ponent Red Sandstone, 

 which is 5,000 feet thie'k in its Southeastern outcrops; 2d, Vespertine, Conglom- 

 erate and sandstone, 2,660 feet in thickness, near the Susquehanna, making a total 

 thickness of 7,660 feet. 



The rocks of the Devonian age are therefore 15,235 feet, or nearly three miles 

 in thickness, and are connected together by their interlocking fossil contents, and 

 united with those of Silurian age, precisely as the Lower Silurian Groups are re- 

 lated to each other. 



The Devonian rocks are followed bj^ . the Carboniferous, which are divided 

 into : 1st, Lower Carboniferous ; 2d, Carboniferous Conglomerate ; 3d, Coal 

 Measures ; and 4th, Permian. 



The Lower Carboniferous Group, in Nova Scotia, consists of reddish and 

 gray sandstones and shales, conglomerates and thick beds of limestone, with ma- 

 rine shells and gypsum, and is 7,636 feet in thickness. On the island of Bona- 

 venture, it is about 2,000 feet in thickness, or with the Carboniferous conglomer- 

 ate 2,766, and contains the Eatonia pecvUari.s, which is found in the Oriskany 

 sandstone of New York. In Illinois, the Lower Carboniferous is subdivided into 

 Groups in ascending order as follows : 1st, Kinderhook Group, from 100 to 150 

 feet ; 2d, Burlington Group, from 25 to 200 feet ; 3d, Keokuk Group, from 100 

 to 150 feet ; 4th, St. Louis Group, from 50 to 200 feet ; and 5th, Chester Group, 

 from 500 to 800 feet. In Missouri, it is subdivided in ascending order, into: 1st, 

 Encrinital limestone ; 2d, Archimedes limestone ; 3d, St. Louis limestone ; 

 and 4th, Ferruginous sandstone ; the maximum thickness of which is only about 

 1,200 feet. The Burlington Group has been called the Encrinital limestone, and 

 in Missouri it is 500 feet thick. The Keokuk limestone is the Archimedes lime- 

 stone of Owen. The Warsaw limestone is sometimes called the second Archi- 

 medes limestone. The St. Louis limestone was called the Concretionary lime- 

 stone by Owen. The Chester Group has been called Kaskaskia limestone. Up- 

 per Archimedes limestone, and Pentremital limestone. In Tennessee, the Lower 

 Carboniferous is subdivided into the Mountain limestone and Siliceous Group. 



