Origin of Granite. 



513 



such probably are the cases which I have sketched. Thus the anom- 

 alous as well as the usual modes in which granite occurs, are explica- 

 ble on this theory : whereas the Neptunian, even if he can show how 

 granite, as it usually occurs, might have resulted from chemical solu- 

 tion in water, cannot by the aqeous theory, explain the anomalies that 

 have been described. 



4. I infer the igneous origin of granite from its chemical effects 

 upon the surrounding strata. 



These effects, so far as I noticed them in the region I have under- 

 taken to describe, have been detailed in various parts of this report; 

 and therefore I need only refer to them in a summary manner. 



The conversion of greywacke slate into flinty slate, and of certain 

 ferruginous portions of it into jasper, as well as the induration of the 

 limestone in the vicinity of the granite in Newport R. Island, are 

 undoubtedly the most striking effects of this kind in the region under 

 consideration. I can conceive of no other hypothesis to account 

 for these changes which is not perfectly absurd. Surely no one can 

 think of explaining such facts by any probable operation of an aqueous 

 agency. And if an igneous agency, sufficient to fuse the graywacke 

 and the limestone be admitted, it must have been sufficient also to fuse 

 the granite. 



The argument which I have drawn from the existence of apparent- 

 ly semi-fused nodules of the schistose rocks in sienite, in favor of the 

 igneous origin of that rock, will apply also to genuine granite on two 

 grounds. 1. Sienite is only a variety of granite: the two rocks being- 

 connected in the same continuous mass,even in the very locality where 

 the conglomerated sienite occurs. And I cannot conceive how one 

 part should have had an igneous and the other an aqueous origin. 2* 

 Similar rounded nodules do occur, though less numerously,in granite- 

 (No. 1486.) 



I have often noticed an appearance on the surface of granite in con- 

 tact with mica slate, which I have not seen described ; but which 

 seems to have some bearing on this question. The surface of the 

 granite has a striated appearance ; as if, when in a plastic slate it had 

 been crowded against the slate while at the same time it was urged 

 upwards. Usually a layer of quartz envelopes the granite, and this 

 is often of a bluish or muddy aspect, as if the coloring matter of the 

 slate had penetrated it. These effects, partly chemical and partly 

 mechanical, are easily explicable on the supposition that the granite 



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