152 



ARCILEAN TIME. 



Michigan, in Sweden, etc; and they occur interstratified with the 

 Archaean schists and quartzyte. They far exceed in thickness the iron 

 ore beds of later ages. In Sussex County, N. J., near Franklin and 

 Stirling, the ore of the great bed is a zinc-iron ore called franklinite. 



Another very common material is graphite (or plumbago), a form of 

 carbon. It occurs disseminated through the rocks, especially the lime- 

 stones, constituting 20 to 30 per cent, of some layers (which therefore 

 are worked for the graphite.) It is often met with in scales through 

 the iron ores ; also in veins which afford it in a purer state, and often 

 crystallized. 



There are, in addition, dioryte, epidotic gneiss and schist; massive hornblende rock 

 and hornblende schist; garnet-euphotide (eclogyte) and a feldspar-euphotide ; soapstone 

 (rensselaerite, p. 72) ; serpentine, ophiolytes or verd-antique marble of different varieties. 



Part of the feldspar related to labradorite has the composition of andesite or anor- 

 thite; and oligoclasc exists in the Swedish rocks. Part of the hypersthenyte contains 

 ordinary hornblende instead of hypersthene, and some kinds, mica or epidote. Good 

 localities for the opalescent labradorite are the streams of the Adirondack, — especially, 

 says Professor Emmons, the beaches of East Eiver ; also Avalanche Lake, near the foot 

 of the great slide from Mount McMartin. 



The potstone or soapstone called rensselaerite covers considerable areas in the towns 

 of Fowler, Canton, Edwards, Hermon, etc., St. Lawrence County, and at Green- 

 ville, in Canada, and is cut into slabs for tables, chimney-pieces, and furnace-linings, 

 or made into inkstands. The parophyte or aluminous potstone of Diana, Lewis County, 

 N. Y., is used for inkstands, etc. 



Beautiful red and green porphyry and a buhrstone are found at Grenville, Canada. 



Among the minerals of the Laurentian rocks, the most common are — Orthoclase, 

 scapolite, nephelite, pyroxene, hornblende, epidote, mica of different kinds, garnet^ 

 tourmaline, zircon, idocrase, sphene, wollastonite, chrondrodite, among silicates; rutile, 

 hematite, magnetite, franklinite, titanic iron, corundum, among oxyds ; apatite, a phos- 

 phate; graphite. The apatite is in some places abundant, and is mined for fertilizing 

 soils. The franklinite of New Jersey is associated with zincite or oxyd of zinc, and 

 willemite, a silicate of zinc. Iolite is a common mineral in Bavaria. 



Lead veins occur in Canada, and near Eossie, New York, affording galenite, blende, 

 and iron and copper pyrites, with calcite and some barite and fluor; but Hunt concludes, 

 from the fact that the vein at Eamsay, Canada, traverses also Silurian rocks, and the 

 latter contain similar veins elsewhere, that all probably belong to a later date, instead 

 of being Archaean. 



Arrangement of the rocks. — Although the Archaean rocks are 

 mostly crystalline, they follow one another in various alternations, 

 like the sedimentary beds of later date. In the sections which have 

 been given, there are alternations of granite, gneiss, schists, lime- 

 stone, etc. ; and the dip and strike may be studied in the same 

 manner as in the case of any tilted sandstones or shales. The follow- 

 ing sections represent other examples ; and in them there are beds 

 of iron-ore, fifty feet and upward in thickness, which are banded 

 with siliceous layers and chlorite schist, showing thereby a distinctly 

 stratified character. Where most flexed or folded, there is still a 

 distinction of layers ; and it is owing to this fact that the rocks may 

 be described as folded ; for folds can be identified only where the 



