512 



Scientific Geology. 



mica slate there exhibits, in many places, where granite is in the vi- 

 cinity, and still maintain that the granite was deposited from aqueous 

 solution, his mind must judge very differently from mine of geologi- 

 cal evidence. When I began geological investigations many years 

 ago, my prejudices were in favor of the Neptunian theory. But an 

 examination of such localities as I have above referred to, showed me 

 at once that I must change sides, or abandon the mountains and study 

 the subject only in the cabinet. In Massachusetts the mechanical in- 

 fluence of granite upon the neighboring rocks is a hundred times 

 more striking than in the case of greenstone; nor can I conceive how 

 any effects of this kind could have resulted from the deposition of 

 granite from aqueous solution. But they would be the natural re- 

 sults of the protrusion of the granite in a melted state. 



It ought however to be understood, that in very many places, where 

 the granite and the straified rocks are in contact, no evidence of the op- 

 eration of a disturbing force appears, except the general evidence re- 

 sulting from the inclined position of the strata. I mean that such cases 

 of disturbance as I have described and sketched, are not common. I 

 explain this in consistency with the igneous origin of granite, by sev- 

 eral considerations. In the first place, it is reasonable to suppose, that 

 originally many of the masses of granite that now appear at the sur- 

 face, were not protruded through the slate; being covered by those 

 strata which have been subsequently worn away. In such case, al- 

 most the only effect which we should expect to find from the forcing 

 upwards of the granite, would be the regular and nearly uniform ele- 

 vation of the strata; since if they were of nearly equal thickness and 

 strength throughout, the molten mass beneath would press almost 

 equally against their entire under surface. In the second place, such 

 a molten mass would soften and partially fuse the strata for a consid- 

 erable thickness above it; and, therefore, it might send veins through 

 the rock thus rendered plastic, without leaving marks of mechanical 

 pressure and disturbance. In the third place, such molten matter 

 would fill all the fissures and cavities previously existing in the strat- 

 ified rocks without producing disturbance. 



These causes, it seems to me, to suggest no others, are sufficient to 

 show why we do not always find evidence of any peculiar disturbance 

 in the strata in contact with granite. But if these strata were not of 

 equal strength or thickness throughout, or if one part of them was less 

 softened by heat than the other parts, then we should expect protru- 

 sions of granite to be the result, with traces of mechanical violence; and 



