154 



ARCILEAN TIME. 



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 western North Carolina, great beds of magnetite, and also of hematite and titanic 

 iron, occur between layers of hornblende schist and mica schist, with intercalated lay- 

 ers at times of jaspery quartz; one of the beds is over 300 yards thick (Genth). 



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 syenyte, with rutile or oxyd of titanium. 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 interstratiried in the same manner with 

 crystalline rocks, — mainly gneiss, hornblende rocks, chlorite slate, clay slate, quartzyte 

 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, 

 chlorite slate and gneiss. At Uto, Sweden, red, jaspery quartz bands the ore, in the 

 same way as in Michigan : the ore — hematite mixed with magnetite — occurs in mica 

 schist and quartzyte, 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, consisting mostly of magnetite, with some hematite. 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 County, N. Y., Emmons), granular limestone 

 is represented in connection with granite and other rocks. In Fig. 212,7 is limestone, 

 without any appearance of stratification; and the containing rock is granite. In 

 Fig. 213, a a are gneiss, b steatyte, I unstratified limestone. Although a and b are not 



Fig. 212. 



Fig. 213. 



evenly stratified, yet they are sufficiently so to show that the limestone, while it has 

 lost its division into layers in the crystallizing process, is probably a conformable 

 stratum. 



The quartzyte of Sauk County, Wisconsin, is referred to the Archaean (Irving). 



The order of stratification among the Archaean rocks is as various 

 as among the rocks of other ages. As sandstones, shales, argilla- 

 ceous sandstones, conglomerates, follow one another in any succession, 

 so granite or gneiss may lie between layers of slate or schist, and 

 quartz rock or limestone may have any place in the series. It is 

 common, however, to find the different hornblendic rocks associated 

 together ; and both these and the chloritic often abound in the iron- 

 regions, since hornblende and chlorite are ferriferous minerals. The 

 association of pyroxene and hornblendic rocks with the limestones 

 has been mentioned above. 



Original condition of the Laurentian beds. — The alternations of 

 hornblendic and other schists with quartzyte, limestone, gneiss, and 

 the other rocks, prove that all were once sedimentary beds, — beds 

 formed by the action of moving water, like the sandstones, argilla- 

 ceous beds, and limestones of later times. They have no resemblance 

 to lavas or igneous ejections. The schists graduate into true slates, and 

 the quartzytes into unmistakable sandstones and conglomerates ; so that 



