WORLD-MAKING I9 



same manner with those below them ; but we find these now 

 associated with great beds of Hmestone and dolomite, which 

 must have been formed by the separation of calcium and mag- 

 nesium carbonates from the sea water, either by chemical pre- 

 cipitation or by the agency of living beings. We have also 

 quartzite, quartzose gneisses, and even pebble beds, which in- 

 form us of sandbanks and shores. Nay, more, we have beds 

 containing graphite which must be the residue of plants, and 

 iron ores which tell of the deoxidation of iron oxide by organic 

 matters. In short, here we have evidence of new factors in 

 world-building, of land and ocean, of atmospheric decay of 

 rocks, of deoxidizing processes carried on by vegetable life on 

 the land and in the waters, of limestone-building in the sea. 

 To afford material for such rocks, the old Ottawa gneiss must 

 have been lifted up into continents and mountain masses by 

 bendings and foldings of the original crust. Under the slow 

 but sure action of the carbon dioxide dissolved in rainwater, 

 its felspar had crumbled down in the course of ages. Its 

 potash, soda, lime, magnesia, and part of its silica had been 

 washed into the sea, there to enter into new combinations 

 and to form new deposits. The crumbling residue of fine clay 

 and sand had been also washed down into the borders of the 

 ocean, and had been there deposited in beds. Thus the 

 earth had enterea mto a new phase, which continues onward 

 through the geological ages ; and I place in the reader's hands 

 one key for unlocking the mystery of the world in affirming 

 that this great change took place, this new era was inaugurated 

 in the midst of the Laurentian period, the oldest of our great 

 divisions of the earth's geological history.^ 



^ I follow the original arrangement of Logan, who first defined this 

 succession in the extensive and excellent exposures of these rocks in Canada. 

 Elsewhere the subject has often been confused and mixed with local de- 

 tails. The same facts, though sometimes under different names, are re- 

 corded by the geologists of Scandinavia, Britain, and the United States, 



