58 JOURNAL OF GEOLOGY—SUPPLEMENT 



area/ It may be noted, moreover, that a broad study of the 

 granites of eastern Massachusetts and Rhode Island, a region which 

 includes the Essex County area, has led Loughlin and Heckinger 

 to the conclusion that the alkaline granites (riebeckite- and aegirite- 

 bearing), though later than the biotite granites, are merely the last 

 product of the general magma represented dominantly by the 

 normal biotite granites^ and are not separated from them by any 

 important period of time. 



A parallel succession, viz., from basic through quartzose to 

 feldspathoid-bearing types, appears to obtain in the post-Cretaceous 

 minor intrusions of the Black Hills of South Dakota.^ Continuous 

 passage from normal granite through syenite to nephelite syenite is 

 shown in the Bancroft area of Ontario.'' In this case, typical alka- 

 line granite is suppressed. According to Loewinson-Lessing, the 

 connection of the miaskite (nephelite-syenite) of the Urals with 

 granite has been shown by Beljankin.^ Kerr concludes that the 

 nephelite syenites, quartz syenites, and other alkahne syenites of the 

 Port Coldwell area are "merely a peripheral differentiation phase 

 of the fundamental gneiss" (granite).^ 



It should be admitted, however, that much is yet to be accom- 

 plished before one can speak with much assurance of the physical 

 chemistry of the problems connected with the interrelations of the 

 alkaUne rocks. It will probably be a long time before important 

 aid in attacking the questions can be expected from the experi- 

 mental side, on account of the difficulty of treating systems contain- 

 ing volatile components. Nevertheless, it is clear that the alkaline 

 rocks belong to a stage of great concentration of these volatile con- 

 stituents and that many of the reactions in the magma depend upon 

 this concentration. The tendency of the increased abundance of 

 these substances, including water and the various mineral acids, is to 



' C. H. Clapp, The Igneous Rocks of Essex County, Massachusetts, abstract of thesis, 

 Massachusetts Institute of Technology, 1910. 



^ Am. Jour. Sci. (4), XXXVIII (1914), 55- 



3 J. P. Iddings, Igneous Rocks, II, 407. 



■f Adams and Barlow, Geol. Survey Canada, Mem. 6, 1910, p. 260. 



5 F. Loewinson-Lessing, "Origin of the Igneous Rocks," Geol. Mag., N.S., Dec. V, 

 Vol. VIII, p. 255. 



^ Ontario Bur. Mines, Ann. Rept., 1910, p. 230. 



