196 PALEOZOIC TIME. 



The Stoekbridge limestone formation (Eolian limestone of Hitchcock) varies in thick- 

 ness from 1,000 to probably 3,000 feet. In Mt. Eolus, East Dorset, Vt., the thickness 

 is 2,000 feet. The upper part of this formation is doubtless Trenton, though its lower 

 portion is referred to the Chazy epoch of the Canadian period. 



{b.) Interior Continental basin. — The Galena or lead-bearing limestone, of Wisconsin 

 and the adjoining States in the West, constitutes the upper portion of the Trenton 

 series, and often alternates with layers of the Trenton limestone. Its color is light gray 

 or yellowish. It is generally magnesian limestone. It is 100 to 200 feet thick in north- 

 ern Illinois; about 250 feet thick near Dubuque, Iowa, and the underlying Trenton 20 

 to 100 feet (Hall). There is usually at base a buff-colored limestone, equivalent to the 

 Black River group. 



In Missouri, there are 350 feet of limestone, the upper 100 called Receptacnlite lime- 

 stone by Shumard. 



In East Tennessee, the formation includes blue limestone, with many fossils, 200 to 

 600 feet thick; and, above, 380 feet of red and gray marble, 400 of bluish shale, and 

 250 of iron-limestone containing the Asaphus PlaUjcephalus. In Middle Tennessee, 

 where the beds are horizontal, there are from 400 to 450 feet of blue limestone (Safford). 



(c.) Arctic region. — The Trenton limestone has been identified upon King William's 

 Island, North Somerset and Boothia. 



2. Utica Epoch. — («.) Interior Continental basin. — The Utica shale is 15 to 35 

 feet thick at Glenn's Falls, in New York; 250 feet in Montgomery County; 300 in 

 Lewis County; 300 near Quebec. 



(b.) Appalachian region. — In Pennsylvania, the rock is a black shale, and in some 

 parts it is fossiliferous. The thickness, given by Professor Rogers, in the Kittatinny, 

 Nippenose, and Nittany valleys is 300 feet, and in the Kishacoquillas valle}' 400 feet. 



3. Cincinnati Epoch — The Hudson River shales cover the region north of 

 Lake Champlain, in Canada, reaching to Quebec, and northeastward to Montmorency 

 and beyond. They also lie over a small area near the centre of the Trenton limestone 

 region of the Ottawa basin. 



In New York, the Hudson River beds include shales and sandstones. They are the 

 Lorraine shales of Jefferson County (the Pulaski shales of the New York Annual Re- 

 ports), containing some thin beds of limestone. The slates along the Hudson River, to 

 which the name was especially applied, have been proved to be in part Primordial, and 

 part, probably, of the Quebec series, (q. v. ) 



In the Green Mountain region, there are 2,000 to 3,000 feet or more of mica schist 

 and slate, hydromica slate, gneiss, quartzyte, and conglomerate, overlying the Stock- 

 bridge limestone, which are probably of the Cincinnati series. They constitute Mount 

 Washington and part or all the Taconic range, Graylock, Tom Ball, Monument Moun- 

 tain and other elevations in Berkshire County, Mass. The quartzyte in many places 

 graduates rather abruptly, in a horizontal direction, into mica schist or slate, or hydro- 

 mica slate or gneiss, showing that its sands were often, when accumulating, a local 



Fig. 316 A. 



Section in eastern part of Great Barrington. 



exposition along shores or shallow flats, while off these shores there were mud deposits 

 — the sands making the quartzyte, and the mud the other rocks, these differing accord- 

 ing to differences in the mud and differences in the degree of metamorphism afterward 

 undergone. Some sections are given on page 213 ; in them, the dotted portions repre- 



