76 BOCK-METAMORPHISM. 



of the ocean. " to " react! ons, which are still 



going on in the ocean's waters, and which have, in past times, 

 given rise directly to limestone strata, in which the occurrence 

 of shells and corals is only accidental" *. That the latter 

 deposits are in the main of organic origin is doubtless the opinion 

 of most geologists ; but a difficulty in connexion with this point 

 has arisen as regards the Archaean hemithrenes. 



To those who believe in "Eozoon," with the exception of 

 Sterry Hunt, the organic origin of the Canadian hemithrenes, it 

 may be assumed, is a settled matter. But it must be admitted, 

 even by those to whom we refer, that there are others who 

 totally dissent from this belief, and who, besides, reject the 

 theory of chemical precipitation. Obviously, then, the onus 

 lies with them to suggest or propose a different solution of the 

 problem. 



It would be rash on our part to deny that organisms of any 

 kind were in existence during the Archaean periods ; but our 

 researches having afforded no proper evidence in support of the 

 affirmative, we are induced to make the attempt to solve the 

 question, as to the origin of the Canadian hemithrenes, other- 

 wise than by the doctrine either of organic intervention, or 

 chemical precipitation. 



Reverting for a moment to the Laurentian silacid rocks, our 

 view as to their origin is based on a full recognition of existing 

 operations pertaining to physical geography : it involves the 

 intervention of mechanical and chemical agencies in effecting 

 the disintegration of rocks already in existen.ee ; also the 

 removal and dispersion of the materials derived therefrom, and 

 their consequent deposition in other and distant areas. It will 

 therefore not be unreasonable to regard the Ontarion funda- 



* ' Geology of Canada/ 1866, pp. 200, 201. The author further declares 

 "the often repeated assertion that organic life has built up all the great 

 limestone formations, is based upon a fallacy ; for animals have no power to 

 generate carbonate of lime." It may therefore be presumed that mollusks, 

 Crustacea, &c. have no power to convert the sulphate of lime, or chloride of 

 calcium (the principal lime constituents of the ocean), into the carbonate 

 of lime of their shells. But as we hold the contrary opinion, we may be 

 allowed to maintain that the shells and corals contained in the limestone are 

 the essential contributors to its formation, and consequently, that " organic 

 life has built up all the great limestone formations." 



