82 THE CANADIAN NATURALIST. [Dec. 



appeared in the primordial division of the Silurian period, is now 

 seen to be immeasurably lengthened beyond its former limit, and 

 to embrace in its domain the most ancient known portions of the 

 earth's crust. It would almost seem as if organic life had been 

 awakened simultaneously with the solidification of the earth's 

 crust. 



The great importance of this discovery cannot be clearly 

 understood, unless we first consider the various and conflicting 

 opinions and theories which had hitherto been maintained 

 concerning the origin of these primary rocks. Thus some, who 

 consider them as the first-formed crust of a previously molten 

 globe, regard their apparent stratification as a kind of concentric 

 parallel structure, developed in the progressive cooling of the mass 

 from without. Others, while admitting a similar origin of these 

 rocks, suppose their division into parallel layers to be due, like the 

 lamination of clay-slates, to lateral pressure. If we admit such 

 views, the igneous origin of schistose rocks becomes conceivable, 

 and is in fact maintained by many. 



On the other hand, we have the school which, while recognizing 

 the sedimentary origin of these crystalline schists, supposes them 

 to have metamorphosed at a later period; either by the internal 

 heat, acting in the deeply buried strata; by the proximity of 

 eruptive rocks ; or finally, through the agency of permeating waters 

 charged with certain mineral salts. 



A few geologists only have hitherto inclined to the opinion that 

 these crystalline schists, while possessing real stratification, and 

 sedimentary in their origin, were formed at a period when the 

 conditions were more favorable to the production of crystalline 

 materials than at present. According to this view, the crystalline 

 structure of these rocks is an original condition, and not one 

 superinduced at a later period by metamorphosis. In order 

 however to arrange and classify these ancient crystalline rocks, it 

 becomes necessary to establish, by superposition or by other 

 evidence, differences in age, such as are recognized in the more 

 recent stratified deposits. The discovery of similar organic 

 remains, occupying a determinate position in the stratification, in 

 different and remote portions of these primitive rocks, furnishes a 

 powerful argument in favor of the latter view, as opposed to the 

 nation which maintains the metamorphic origin of the various 

 minerals and rocks of these ancient formations ; so that we may 

 regard the direct formation of these mineral elements, at least so 



