PALEOZOIC TIME — UPPER SILURIAN. 643 



portion of the column. In Virginia the Clinton consists of sandstones and shales, mostly 

 sandy, having an estimated thickness of not far from 850'. Beds of fossil or calcareous 

 ore are present from central Pennsylvania to Alabama. (J. J. S.) 



In east Tennessee the rocks are 200' to 300' thick, and include one or tw^o beds of the 

 oolitic iron ore. 



In western Kentucky the oolitic red ore beds occur in Montgomery, Bath, and 

 Fleming counties and along Pine Mountain. 



(c) Eastern Border region. — In Nova Scotia, at Arisaig, which is within the Acadian 

 trough, the rocks are shales and limestone, and have a thickness of about 500'. At the 

 East River of Pictou, there are also slates and calcareous bands, probably of the same 

 age. They include a deposit of oolitic iron ore, like that of the Clinton rocks of central 

 New York, which in some places has a thickness of 40'. In southern New Brunswick the 

 beds are like the Arisaig. 



The fossiliferous Upper Silurian rocks of the coast of Maine, on the borders of the 

 same Acadian trough, are described in Hitchcock's Beport on 3Iaine, 1861, and in papers 

 by W. 0. Crosby, Am. Jour. Sc, xxiii., 1862 ; N. S. Shaler, ib., xxxii., 1886 ; Dodge and 

 Beecher, ib., xliii., 1892. See also Foerste, on the iron ore, ib., xli., 1891 ; and Smyth, on 

 the same, ib., xliii., 1892. 



3. Niagara Geocp. — (a) Interior Continental basin. — At Rochester, N.Y., there 

 are about 80' of limestone, overlying 80' of shale ; and the limestone makes nearly the 

 whole height of the upper fall. At Lockport there is a fine exhibition of the rock, and it 

 includes an "encrinital" layer, which is mottled with red, and over it a bed full of deli- 

 cate Corals. The limestone in some places breaks vertically into small columns, and such 

 specimens have been called Stylolites. The structure is due, as explained by Marsh, to a 

 slipping, through vertical pressure, of a part capped by a fossil shell against an adjoining 

 part not so capped. Such Stylolites occur in limestones of other periods from the Cam- 

 brian to the Carboniferous. 



The " Coralline limestone " is only 4' thick at the base of the Heldei-berg Mountains ; 

 but at Nearpass's quarry, south of Port Jervis, it is 50' thick, and contains numerous 

 Niagara fossils. 



The Guelph limestone (a dolomyte), well seen at Gait and Guelph, in Ontario, western 

 Canada, and farther west (formerly supposed to be of the age of the Salina beds), is the 

 upper part of the Niagara limestone. The thickness in Ontario is about 160'. 



The Niagara limestone and shale extend through Ohio and Indiana to Wisconsin and 

 Iowa. But it is wanting in southern Illinois. The "Clear Creek limestone" of Union, 

 Jackson, and Alexander counties is probably Lower Helderberg (Worthen). The rock 

 has a wide distribution in Iowa (where it is in part the Leclaire limestone). Much of it 

 is cherty, and has the fossils silicified. An analysis, by J. D. "Whitney, of a specimen from 

 Makoqueta County, Iowa, obtained calcium carbonate 52-18, magnesium carbonate 42-64, 

 with 0-35*of sodium carbonate, traces of potash, iron carbonate, and sulphuric acid, 0-63 

 of alumina and iron sesquioxide, and 4-00 insoluble in acid. The beds form the summits 

 of some of the mounds, as Table Mound, near Dubuque. 



In west Tennessee the Meniscus limestone, 150' to 200' thick, noted for its fossil 

 sponges, of which one is meniscus-shaped, is ]3robably the equivalent of the Niagara 

 limestone. 



The Niagara beds of the Black Hills, near Deadwood, were identified through their 

 fossils, by C. E. Beecher. In the Deadwood section there are Cambrian beds below, rest- 

 ing on Archaean ; above, there is the Carboniferous limestone, with probably Devonian 

 strata between. 



(5) Appalachian region. — The Niagara has not been recognized distinctly in Penn- 

 sylvania ; though in the central and southern portion of the state there occurs, at varying 

 distances above the uppermost bed of iron ore, a succession of very thin limestones, which, 

 in many localities, contain Niagara forms. This has been placed by Lesley in the lower 



