LOWER SILURIAN. 197 



II. Economical Products. 



The Galena limestone, of Wisconsin and the adjoining portions of 

 Dlinois 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 

 may be 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 

 Utica shale ; and another from the Hudson River beds at Guilderland, 

 near Albany, N. Y. 



The black Utica shale abounds in combustible material, although 

 containing no coal. Whitney found about 21 per cent, in the shale of 

 Savannah, 111. ; 11 to 16 per cent, in that of Dubuque; and 12 to 

 14 per cent, in that of Herkimer County, N. Y. 



The Trenton formation in East Tennessee affords a reddish varie- 

 gated marble of great beauty, and also a grayish-white variety, which 

 are extensively worked and exported. 



HE. Life. 



1. Plants. 



Sea- weeds are the only known fossil plants, and specimens are rare. 

 Two of the species are represented in Figs. 316 B, C. 



Fig. 316 B is the Butkotrephis gracilis H., and Fig. 316 C, B. succulosus H. The figures 

 represent only portions of these plants. 



Remains of land plants have been announced as occurring in beds 

 of the Hudson River group in Ohio and Kentucky by Lesquereux ; 

 and Figs. 316 D, E, F, represent three of the species named by 

 him. One (316 E), from near Cincinnati, is supposed to be related to 

 the Ground Pine, or Lycopods ; another is a Fern (316 F) from the 



