234 ^^^ POPULAR SCIENCE MONTHLY. 



once water-drifted beds metamorphosed, transfigured, as it were, by- 

 heat and pressure into this adamantine pavement ; and, further, we 

 find that they must have been so formed in the attrition and decay 

 of yet oUier continents. The dim perspective opens backward to the 

 very verge of chaos. 



After deposition, and in a somewhat consolidated state, they were 

 slowly raised, their emergence above the water accompanied a contrac- 

 tion of the earth's crust, and the flexible series, from top to bottom, 

 folded up in deep and multiplied plications. Mountain-chains arose, 

 their strata tilted up, contorted and complicated in related groups of 

 synclinal and anticlinal axes, and, by the effective agency of heat and 

 aqueous distillation through the myriad pores of the rock, a minera- 

 logical change ensued. The argillaceous muds were hardened into 

 slates and schists, the calcareous shoals became crystalline limestones, 

 marbles, and dolomites, the siliceous bands became quartzites and sand- 

 stones, the iron slime crystallized into colossal sheets of iron-ore, mag- 

 nesian sediments became serpentine, and through all there developed 

 beautiful minerals under various associations and marking different 

 horizons in this complex pile of natural masonry. Feldspars, pyrox- 

 ene, mica, apatite, chondrodite, epidote, and garnet are a few of many 

 which, in crevice and seam, and scattered through the matrix rock, 

 remain as token, and possibly revelation, of the changes here enacted. 

 From this archtean country come the magnetic oxide of the Adiron- 

 dacks, the hematite of Marquette, the soft lead of Ticonderoga, the 

 dolomite of Westchester County, the mica of North Carolina, the sye- 

 nites and granites of Maine, the marbles of Vermont, the tinstone of 

 New Hampshire, and the phosphates of Canada. Over thirty thousand 

 feet in vertical thickness is the estimated depth of this gigantic mass 

 fitting foundation for the arches of the world. 



Recent study, notably that of Dr. T. Sterry Hunt, separates this 

 wonderful epoch into four secondary ones of unequal duration and 

 varying character. First, the Laurentian, a name given by the Geo- 

 logical Survey of Canada and applied originally to the rocks of the 

 Laurentian highlands, those abraded swells of land which overlook the 

 St. Lawrence and rise in rugged grandeur four thousand feet high 

 above the shadowed waters of the Saguenay. This primitive tract of 

 archa3an territory embraces the Adirondacks of New York, the region 

 about Ottawa, portions of Newfoundland, and probably includes the 

 rock assigned to this age in Massachusetts, Connecticut, and Rhode 

 Island, and the long back which makes up the Highlands of the Hud- 

 son, the South Mountain of New Jersey, and the ridges about Rich- 

 mond and Mount Roan in North Carolina. The rock is " a strong, 

 massive gneiss, reddish or grayish in color." 



Following this is the Norian, unconformable with the Laurentian, 

 viz., not fitting into it, as though the latter, first made under water, 

 solidified and raised, had again been depressed and received these sec- 



