Vol. 50.] BASIC ERUPTIVE ROCKS OF GRAN. 23 



apart from'my main subject, I must defer observations in connexion 

 therewith to another occasion. 



The small and insignificant basic abyssal masses of Gran are nol 

 in themselves of sufficient importance to justify me in occupying the 

 time of this Society by describing them. There are, however, other 

 circumstances, not as yet referred to, which give them great interest . 

 They are accompanied by a great series of dykes and sheets, the 

 study of which throws much light on those processes of differentia- 

 tion which are just at present being made the object of thorough 

 research by petrologists and geologists. 



IV. The Camptonites and Bostonites. 



Along both sides of the entire fissure-line on which the abyssal 

 rocks are situated, we find an innumerable multitude of dykes and 

 sheets of camptonite and bostonite, two kinds of rock which have 

 formerly been admitted to be closely associated with masses of 

 nepheline-syenite. 



Camptonite (lamprophyric dyke-rock essentially composed of basic 

 plagioclase and brown basaltic hornblende, often porphyritic from 

 phenocrysts of the latter mineral) has been previously described 

 from Campton Falls in Xew Hampshire l ; Montreal in Canada 2 ; 

 Forest of Dean in Orange Co., N". Y. 3 ; Fort Montgomery (Fairhaven, 

 Proctor, etc.) in the Hudson River Highlands 4 ; Whitehall in Wash- 

 ington Co., K. Y. 5 ; Lake Champlain Valley e ; nearly allied rocks, 

 though hardly typical camptonites, are described from Val Avisio in 

 the Tyrol 7 ; Inchnadampf in the Scottish Highlands * ; Waldmichel- 

 bach and other localities in the Spessart. 9 



The name ' bostonite' was introduced by Bosenbusch and applied to 

 dyke-rocks with trachytic structure, essentially composed of felspars 

 without dark minerals ; a more detailed description is given by 

 Kemp. Bostonites are known from Marblehead near Boston. 10 

 Montreal in Canada, 10 Serra de Tingua in Brazil, 11 and from Lake 

 Champlain Valley. 1 " In all previously described occurrences the 

 bostonites are connected with different basic dyke-rocks, and with 

 masses of nepheline-syenite (?) in the vicinity ; among the asso- 

 ciated basic rocks near Montreal and Lake Champlain there are 

 also camptonites. 



1 G. W. Hawes, Am. Journ. Sci. ser. 3, vol. xvii. (1S79) p. 147. 



2 B. J. Harrington, Geol. Surv. of Canada, Report for 1S77-78 Of, p. 42. 



3 ,T. F. Kemp, Am. Journ. Sci. ser. 3, vol. xxxv. (1888) p. 331. 



4 Id. ' Amer. Naturalist' for 1888, p. 691. 



5 Id. and V. F. Marsters, ' Amer. Geologist,' vol. iv. (1889) p. 97. 



6 J. F. Kemp aud V. F. Marsters, Trans. JN". Y. Acad. Sci. vol. xi. (1891) 

 p. 13. 



7 Corn. Hotter, Tschermak's Min. Mitfk. (1875) pp. 179. ISO. 304 ; A. Cath- 

 rein, Zeitschr. f. Krystallogr. u. Min. vol. viii. (1884) p. 221. 



8 J. J. H. Teall, Geol. Mag. for 188C, p. 346. 



9 Erw. Goller, Inaug. Diss. (Strassburg, 1889). 



10 On literature, see Kemp aud Marsters, op. supra cit. p. 17. 



11 M. Hunter and II. Eosenbusch. TsL-hemiak's Min. u. Petr. Mitth. vol. xi. 

 (1890) p. 445. 



12 Kemp aud Marsters. op. supra cit. 



