LOWER SILURIAN. 197 



sent quartzyte, the blocked, limestone, and the others the schist, slate, or gneiss. 

 While, in Monument Mountain (Fig. 395 A), there are, over the limestone, two strata of 

 schist (or gneiss) alternating with two of quartzyte, in other sections the lower quartz- 

 yte, or the lower schist, is absent, and, in the more western hills (Tom Ball, and the 

 Taconic) all the quartzyte is wanting. In the annexed section, toward the right or east 

 end, the quartzyte, limestone, and gneiss (or mica schist) alternate; while on the west 

 side of the same valley (left end of section) there is quartzyte, with a narrow band of 

 mica schist in it, which becomes quartzyte a hundred feet to the south; and above the 

 quartzyte, gneiss. 



The thickness of the shales, in Schoharie County, N. Y., is 700 feet; near Quebec, 

 2,000 feet; in western Canada, 700 feet; on Lake Huron, 180 feet; in the Michigan 

 Peninsula, 18 feet; in Iowa, 25 to 100 feet. In Missouri, there are alternations of shale 

 and sandstone, w r ith some limestone, 100 to 200 feet in total thickness; at Cincinnati, 

 shales and limestones, 700 feet thick. In Middle Tennessee, the Cincinnati series in- 

 cludes the Nashville group of Safford, and consists of argillaceous limestone, with 

 many shaly layers, about 500 feet thick. In East Tennessee, the beds (corresponding 

 to both the Utica and Hudson River epochs) are of great extent, and consist of blue 

 calcareous and more or less sandy shales, with some thin layers of calcareous sand- 

 stone. They also occur of great thickness in Virginia, and reach down to Alabama. 



In Pennsylvania, in the Kishicoquillas valley, the rock is a blue shale and slate, with 

 some thin layers of calcareous sandstone, and the thickness is 1,200 feet; in the Nittany 

 valley, 700 feet; in the Nippenose valley, a little less. (Rogers.) 



The limestone formation on the island of Anticosti has a total thickness of nearly 

 2,400 feet, and is divided by Logan into five parts — the first, or lowest, 959 feet thick; 

 the second, about 300 feet thick; the third, about 450 feet: the fourth, about 550 feet; 

 the fifth, 70 feet. The first two are referred to the Trenton period, and the rest to the 

 Upper Silurian. There are thin beds of shales in the series. The rocks are nearly 

 horizontal. 



II. Economical Products. 



The Galena limestone, of Wisconsin and the adjoining portions of 

 Illinois and Iowa, is noted for its yield of lead ore. The ore is the 

 ordinary sulphid of lead, or Galenite. It occupies vast cavities, rather 

 than veins, in the limestone, which cavities were filled from above. 



The lead-region of Wisconsin and Illinois, according to Owen, is 87 miles from east 

 to west, and 54 from north to south ; and throughout much of this region traces of lead 

 maybe found. The beds resemble in position the lead-mines of Missouri; but the 

 latter occur in a limestone of the Calciferous epoch. These mines of the Upper Missis- 

 sippi have been the subject of a report (1854) by J. D. Whitney. The galenite is often 

 in large crystals, and is associated with sphalerite (zinc blende or "black jack"), 

 Smithsonite (carbonate of zinc), pyrite, and marcasite, and occasionally barite (heavy 

 spar), anglesite (sulphate of lead), chalcopyrite, azurite and zinc bloom. The Smith- 

 sonite (dry-bone of the miners) constitutes pseudomorphs at Mineral Point, Shullsburg, 

 etc., in Wisconsin, after sphalerite and calcite. Beautiful stalactites of marcasite occur 

 near Galena, at Marsden's Diggings. 



Both the Trenton limestone and the Utica and Hudson River shales 

 afford in some places mineral oil. It occurs sparingly in the Tren- 

 ton, at Riviere a la Rosa (Montmorenci), in Canada; at Pakenham, 

 Canada, in large Orthocerata ; at Watertown, N. Y., in drops in 

 fossil coral. In Kentucky, the blue limestone yields oil very abun- 

 dantly. On Grand Manitoulin Island, Canada, a spring rises from the 



