ARRANGEMENT OF AZOIC ROCKS. 



141 



ore in i is banded with jasper. In figs. 142 and 143 (Essex co., N.Y., 

 Emmons) the iron-ore. in beds several yards wide, is associated with gneiss 

 and quartz rock, and is interlaminated with 

 quartz, the whole dipping together in a 

 common direction, like beds of sandstone, 

 shale, and iron-ore in many regions of sedi- 

 mentary rocks. 



In fig. 144 (Penokie Range, south of Lake 

 Superior, C. Whittlesey) h is hornblende rock 

 and slaty quartz; g, quartzite, 30 feet thick; 

 i, a bed of iron-ore, 25 to 50 feet thick. 



In another section, by C. Whittlesey (described in Foster & Whitney's Report), 

 taken at the falls of the Menomonee, there are alternations of gneiss, horn- 

 blende, and quartz rock with talcose and chloritic schists, quartzite, and granu- 

 lar limestone, and between the limestone layers there is a layer of iron-ore, — 

 .showing again that the iron-ore is in beds conformable with the schists. The 

 beds, however, may not have great lateral extent; for the iron may be local in 

 bands, or imbedded in other kinds of rocks. 



In the Missouri region, at Pilot Knob, the ore-strata (says J. D. Whitney) 

 consist of a series of quartzose beds of great thickness, passing gradually into 

 specular iron, which frequently forms bands of nearly pure ore, alternating 

 Avith bands of quartz more or less mixed with the iron. The ore, moreover, 

 is often thin-laminated. 



At the Adirondack mines, in Essex co., N.Y., one bed, according to Emmons, 

 is 150 feet thick, and another exceeds 700 feet. In the Michigan region they 

 are on the same great scale. In Missouri, one of the "iron mountains" — the 

 Pilot Knob — is 581 feet high, and the other 228 feet ; ' and huge displaced 

 masses, some ten and twenty tons' weight, lie over the surface. The iron-ore in 

 each of these regions is partly magnetic and partly specular ore, or hematite,— 

 that of Lake Superior and Missouri mostly the latter, and that of New York 

 mainly the former. 



In. Canada, at Bay St. Paul's, there is a bed of titanic iron 90 feet wide, 

 exposed for 200 or 300 feet, occurring in syenite with rutile or oxyd of tita- 

 nium. The ore does not differ from ordinary specular iron in appearance, but 

 the powder is not red. In Sweden and Norway the iron-ores are interstrati- 

 fied in the same manner with crystalline rocks, — mainly gneiss, hornblende 

 rocks, talcose and chloritic schists, argillaceous schists, quartzite, and granular 

 limestone, with which they are more or less laminated. At Dannemora, the 

 stratum containing iron is 600 feet in width; and it occurs with granular 

 limestone, talcose and chloritic schists, and gneiss. At Uto, Sweden, red, 

 jaspery quartz bands the ore, in the same way as in Michigan; the ore — the 

 specular mixed with the magnetic — occurs in mica schist and quartzite, in an 

 irregularly-shaped mass, about 120 feet in its widest part. At Gellivara there 

 is an iron mountain three or four miles long and one and a half wide, consist- 

 ing mostly of magnetic iron-ore, with some specular ore. In each of these 

 regions the beds dip with the enclosing rock, — showing that all have had a 

 common history. 



In the annexed sections (St. Lawrence co., N.Y., Emmons), granular lime- 



