"CRYSTALLINE LIMESTONES OF CANADA. 77 



mental " unstratified gneisso-syenitic series " as the rocks which 

 yielded the silicates of alumina, magnesia, and lime, the alka- 

 line silicates, and the oxides of iron, that gave rise to the sands, 

 muds, and agglomerates of the overlying Laurentians. While 

 the assumed mechanical actions were going on the carbonic acid 

 of the water and atmosphere would doubtless act on the calcic, 

 magnesian, and alkaline silicates ; next would necessarily follow 

 the conversion of the latter into soluble carbonates. 



Besides other resultants, bicarbonate of lime would be gene- 

 rated, and forthwith conveyed by rivers into lakes and seas. 

 Having never denied the existence of plants or animals during 

 the Archaean periods, we see no reason why some of the lime 

 salt, as above generated, may not have contributed to the for- 

 mation of organic skeletons ; but this yet remains to be proved. 

 We must also admit the probability that in shallow seas and 

 lagoons, also along shores, carbonate of lime would be thrown 

 clown by the evaporation of their water ; and it may be equally 

 admitted that the water under certain conditions would other- 

 wise part with it. In this way may have been formed deposits 

 of limestone, but comparatively insignificant in quantity, while 

 carbonate of lime may have become intermixed with the com- 

 ponents of other shallow-water deposits. The calcareous base 

 of the conglomerates near the Coulonge river, Co. Ottawa, 

 strikes us as being probably a littoral formation. 



But with respect to the 6000 feet of " crystalline limestones " 

 the silo-carbacid members of the Laurentians we must hold 

 to a different explanation of their origin. 



Without availing ourselves of heat emanating from contiguous 

 masses of molten rocks, we shall simply assume that before the 

 Laurentian deposits were thrown out of their original position, 

 a considerable portion (being buried at great depths and under 

 enormous pressure, and retaining their original water) became 

 affected by the elevated temperatures prevailing at such depths; 

 and thus they passed into the mineralized condition character- 

 istic of ordinary rnetamorphic rocks. Afterwards, through the 

 introduction of extraneous water containing a carbacid solution, 

 these mineralized metamorphics became chemically changed into 

 hernithrenes and other related rocks. 



In support of this view we might appeal to evidences, already 

 described, of the most conclusive kind those yielded by the 



