382 PROPOSED MODIFICATION [Ch. XVI. 



rendered probable by the phenomena of volcanos, the high 

 temperature of deep mines and of mineral springs, supported 

 moreover bj the approval of some eminent astronomers, it 

 may be adopted as the first step towards the erection of a 

 theory of the earth. 



At this stage of the speculation, we might indulge in va- 

 rious fancies, as to the precise order and mode of consolid- 

 ation, and as to the condition of the aerial and aqueous 

 fluids during the secular refrigeration of the surface of the 

 igneous mass. We have, however, been anticipated therein, 

 by French as well as by British geologists ; and though we 

 might suggest some modifications of their views, yet we 

 prefer commencing at the period when the exterior of the 

 earth was so far solidified and reduced in temperature, as to 

 admit of the combined co-operation of igneous, aqueous, and 

 atmospheric agencies, similar to those which now modify the 

 form and condition of the superficial parts of our planet. 



At this early period in the history of the earth, we conceive 

 that all the rocks belonged to that class, commonly called 

 primary, which has been the subject of our consideration ; 

 that is, they were not all granitic, as is generally supposed, 

 but also schistose ; both kinds being intermixed, sometimes 

 the one and sometimes the other predominating in certain 

 portions of the earth, and associated together under precisely 

 the same arrangements as those now observed in the primary 

 formations. On this view of the contemporaneous origin of 

 the granitic and schistose rocks, we may easily comprehend 

 numerous phenomena which appear to be exceedingly com- 

 plicated, on the supposition of these rocks being of distinct 

 and diverse natures the one of igneous and the other of 

 aqueous derivation. Thus, if the various kinds of granite 

 and schist were formed at the same time, they might be ex- 

 pected during consolidation to assume similar concretionary 

 structures. And it is, therefore, not surprising that the 

 layers or beds resulting from the extensive aggregation of 

 such concretions, should often pass through both rocks, or 



