188 GRANITES AND GRANITIC VEIN-STONES. [XI. 



mines of the Keweenaw peninsula, on the south shore of the 

 same lake, is made up in large part of the ruins of similar 

 orthophyres.] 



6. Many of the so-called granites of New England are 

 true gneisses ; as, for example, those quarried in Augusta, Hal- 

 lowell, Brunswick, and many other places in Maine, which are 

 indigenous rocks interstratified with the micaceous and horn- 

 blendic schists of the great White Mountain series. To this 

 class also, judging from lithological characters, belong the so- 

 called granites of Concord and Fitzwilliarn, New Hampshire. 

 These indigenous rocks are tenderer, less coherent, and gener- 

 ally finer grained than the eruptive granites, of which we have 

 examples in the micaceous granite of Biddeford, Maine, and 

 the hornblendic granites of Marblehead and Stoneham, Massa- 

 chusetts, and Newport, Ehode Island, in all of which localities 

 the contact of the eruptive mass with the enclosing rock is 

 plainly seen, as is also the case farther eastward, on the St. 

 Croix and St. John's Eivers in New Brunswick, and in the 

 Cobequid Hills and elsewhere in Nova Scotia. The horn- 

 blendic granites of Gloucester, Salem, and Quincy, Massachu- 

 setts, seem also, from their lithological characters, to belong to 

 the class of exotic or true eruptive granites.* The further dis- 

 cussion of the nature and origin of these gneisses and granites 

 is reserved for another occasion, and we now proceed to notice 

 the history of granitic veins. 



7. The eruptive granitic masses just noticed not only in- 

 clude fragments of the adjacent rocks, especially near the line 

 of contact, but very often send off dikes or veins into the sur- 

 rounding strata. The relation of these with the parent mass is 

 however generally obvious, and it may be seen that they do 

 not differ from it except in being often finer grained. These 

 injected or intruded veins are not to be confounded with a 

 third class of granitic aggregates, which I have elsewhere 

 described as granitic vein-stones, or, to express their supposed 



* T. S. Hunt on the Geology of Eastern New England, American Journal 

 of Science for July, 1870, p. 88; also Notes on the Geology of the Vicinity of 

 Boston, Proc. Boston Nat. Hist. Soc., Oct. 19, 1870. 



