558 Remarks on Dr. Boast's Primary Geology. 



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 formed from materials deposited and 

 arranged by water ; the other, by the action of an internal fire, at 

 considerable depths below the surface. These conclusions are said 

 to be founded on physical evidence, — on facts recorded by numerous 

 observers in various parts of the world : and it may therefore appear 

 to be an idle waste of time, an attempt of no little presumption, to 

 make even a show of assaulting a position so strongly fortified. 

 There is no intention of disputing the correctness of the facts, when 

 such have been sufficiently investigated and faithfully described ; but 

 the evidence which these afford, may be sometimes disputed : for 

 what is this physical evidence of which we so often hear, and to 

 which theorists so frequently appeal ? It is only a testimony re- 

 corded in hieroglyphics of an unknown character, and which may 

 therefore admit of divers interpretations. In our attempts to deci- 

 pher these characters, no solution can be admissible, unless it be 

 applicable to all without exception. Now, the prevailing theory 

 satisfactorily explains a great body of these facts, but it will be the 

 object of the following pages to show that there are some phenomena 

 which it does not appear to interpret in a clear and convincing 

 manner. For instance, we are taught that gneiss, and other primary 

 strata, which so nearly resemble the granitic rocks, especially at 

 their junction with each other, are merely sedimentary deposits 

 altered by the contact of granite in a state of fusion ; and, that the 

 condition of secondary strata next to trap-rocks, clearly indicates that 

 such changes do take place under similar circumstances : but, after 

 making every allowance for the comparison of small things with 

 great, we shall strive to show that the cases compared are not 

 analogous ; that the evidence brought forward bears witness to 

 changes produced by heat, but not to such changes as the primary 

 strata are supposed to have undergone ; viz., an assimilation of 

 the aqueous to the igneous rocks, by the introduction of additional 

 elements into the composition of the former. 



