386 PROPOSED MODIFICATION [Ch.XVI. 



analogous to modern productions. Notwithstanding, it would 

 be preferable to adopt, in place of the term primary, some 

 other, not conveying a theoretical signification ; for even that 

 of granitiferous, which we have sometimes used, is not entirely 

 free from objection, since some intrusive porphyries and traps 

 mineralogically resemble the granitic rocks. 



Having stated our conjectures concerning the primary 

 formations in their original condition, we now proceed to point 

 out in what manner they maybe conjoined with the prevailing 

 theory concerning those rocks which have been subsequently 

 formed. 



The primary rocks, at the earliest period of the existing 

 order of things on the earth's surface, appear to have been 

 subject to the chemical and mechanical actions of the elements : 

 by the former of which they have been, to a certain extent, 

 successively decomposed and disintegrated ; and by the latter, 

 degraded and converted into gravel, sand, clay, and like 

 incoherent substances, capable of being transported into new 

 localities. 



Such deposits have been derived from the primary rocks 

 during every geological epoch, but not always in the same 

 ratio, inasmuch as they have gradually covered up and pro- 

 tected these rocks from the elements, and have in their turn 

 become exposed to the same destructive influence; and thus it 

 is, that recent transported deposits are seldom of an unmixed 

 character, being wholly composed of the debris of primary 

 rocks only in their immediate vicinity. In like manner, also, 

 newer deposits are conjoined with the granite at the surface, 

 either covering older ones or immediately resting on the pri- 

 mary rock : the precise order of these depositions depends 

 on the combination of various circumstances ; among the most 

 important of which may be enumerated, the relative levels of 

 sea and land, previous to and succeeding such formations, 

 the degree of power possessed by the transporting agent, and 

 the form and position of the surfaces on which the deposits 

 took place. 



