RELATIONS OF SCHIST AND GRANITE. 211 



the bounding lines between the schist and granite to be always sharp. His 

 conclusion is that the relations are what they would he if the granite were 

 intrusive, and the schist areas fragments caught in it. This conclusion for 

 a part of the granite was first questioned, so far as I know, by Emmons, who 

 -peaks of one of the ridges as being pegmatitic. Carpenter regards all the 

 granite as metamorphic ; Crosby considers it all pegmatitic. 



It seems to me, however, that neither Crosby's nor Carpenter's theory of 

 the origin of the granite sufficiently explains the facts upon which Newton 

 based his opinion that it is in the main eruptive. Also, it will be noted that 

 all my own observations as to the relations of the granite and schists bear 

 toward an eruptive origin for it. The distribution of the two rocks is ex- 

 actly wdiat we would expect if a great mass of molten material had been 

 forced up from deep within the earth, thrusting aside the slates, breaking 

 and penetrating them by apophyses. Further, as has been seen, the fact 

 that the schists strike everywhere parallel to the granite core and dip away 

 from it is just what would happen if this were the case. Later, when the 

 lithological character of the schists are considered, it will be seen that they 

 also furnish important corroborative evidence of this conclusion. The gran- 

 ite core, the adjacent great granite masses, and the large granite ridges are 

 in general of much the same character, except that there is a variation in 

 coarseness of grain. The small ridges or veins remote from the central 

 masses become at times more quartzose than the average rock, and in a few 

 cases have to some extent a vein structure. It is quite conceivable, indeed 

 probable, that locally subsequent infiltration has played a relatively impor- 

 tant part, or even that some of the veins are wholly pegmatitic ; and this is 

 particularly likely to be the case with those which have been most closely 

 examined — i. e., those bearing a small percentage of cassiterite. How a part 

 of the granite may be pegmatitic when its great mass is eruptive is easier 

 to understand than upon the hypothesis that, with no known exceptional 

 causes, immense masses of metamorphic or pegmatitic granite have formed 

 within the slates and schists, and yet everywhere are sharply separated from 

 them . 



A second crystalline schist area has been noted in the northern hills. 

 Here it will be remembered are abundantly found comparatively late erup- 

 tives — rhyolites, trachytes, etc. The quantity of the dikes of these materials 

 over considerable areas is so great as to compose a large part, at least a 

 third, of the total mass of the rock. Also, contained in these later volcanics, 

 have been found by Newton fragments of granite precisely like that occur- 

 ring to the south. The presence of crystalline schists in the northern hills 

 associated with these volcanics is suggestive of their origin, when taken in 

 connection with the fact that the schists of the south are associated with 

 rocks presumably eruptive. It may be conceived that these crystalline 



XXVrn— Hum.. Groi,. Soc. A.m., \'<«.. 1, 1889. 



