CONTEMPOEAHIES AND SUCCESSOES OF EOZOON. 143 



'' On the other hand^ we have the school which^ while 

 recognising the sedimentary origin of these crystalline 

 schists^ supposes them to have been 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 favourable to the production of crystalline ma- 

 terials than at present. According to this view, the 

 crystalline structure of these rocks is an original con- 

 dition, 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 recognised in 

 the more recent stratified deposits. The discovery of 

 similar organic remains, occupying a determinate po- 

 sition in the stratification, in difierent and remote 

 portions of these primitive rocks, furnishes a powerful 

 argument in favour of the latter view, as opposed to 

 the notion which maintains the metamorphic origin of 

 the various minerals and rocks of these ancient forma- 

 tions ; so that we may regard the direct formation of 

 these mineral elements, at least so far as these fossili- 

 ferous primary limestones are concerned, as an es- 

 tablished fact.''^ 



