226 PREVAILING THEORY CONCERNING [Ch. XI. 



formations, had taken place. We conceive, therefore, that 

 the relative age of the visible primary rocks, as compared to 

 the unaltered sedimentary strata, must always be determined 

 by the relation of two forces, the power which uplifts the 

 primary rocks, and that aqueous agency which degrades and 

 renovates the earth's surface; or, in other words, it must 

 depend on the quantity of aqueous action which takes place 

 between two periods, that when the heated and melted 

 rocks are cooled and consolidated in the nether regions, and 

 that when the same emerge to the day." 



" The principal effect of these volcanic operations in the 

 nether regions, during the tertiary periods, or since the exist- 

 ing species began to flourish, has been, to heave up the sur- 

 face of primary formations of an age anterior to the carboni- 

 ferous. We imagine that the repetition of another series of 

 movements of equal violence, might upraise rocks similar to 

 the primary, produced during the secondary periods : and, if 

 the same force should still continue to act, the next con- 

 vulsions might bring up those belonging to the tertiary and 

 recent epochs, by which time we imagine that nearly all the 

 sedimentary strata, now in sight, would either have been 

 destroyed by the action of water, or would have assumed 

 the structure of the primary stratified rocks, or would have 

 been melted down into granitic or volcanic rocks." 



Having now given a general view of the prevailing theory 

 concerning the primary rocks, and having endeavoured to 

 elucidate the same by copious extracts from LyelPs " Prin- 

 ciples of Geology," we proceed to point out those parts of the 

 theory which appear to be objectionable; and to state the 

 order in which it is proposed to conduct the discussion on 

 which we are now about to enter. 



It is laid down, as a fundamental principle of this theory, 

 that the primary rocks consist of two distinct classes; not 

 distinguished from each other for the sake of facilitating 

 scientific descriptions^ but severed by well-marked characters, 

 and by natures diametrically opposite : the one having been 



