388 THE CANADIAN NATURALIST. [Dec. 



thing in common with that of the Mediterranean, — a fact which 

 has an important connexion with the suggestions we have made in 

 this paper. 



NOTES OX GRANITIC ROCKS. 



By T. Sterry Hunt, LL.D., F.R.S.^ 



First and Second Parts. 



Eead before the American Association for the Advancement of Science 



at Troy, August 20, 1870. 



Contents of Sections. — §1-2, Definitions of granite and syenite; § 3 

 Structure of granitic and gneissic rocks ; § 4-5, Felsites and felsite- 

 porphyries; § 6, Gneisses and granites of Xew England; $7, Granitic 

 dykes and granitic vein-stones; §8, Scheerer's theory of granitic 

 veins; § 9-10. Elie dc Beaumont on granites and granitic emanations; 

 § 11, Granitic distinguished from concretionary veins; §12, Yon Cotta 

 on granitic veins ; § 13-14. The authors views on the concretionary ori- 

 gin of granitic veins; §15. The banded structure of granitic veins ; §16, 

 Granitic veins of Maine, Brunswick; § 17, Topsham, Paris; § 18, 

 WestbrookjLewiston; crystallinelimestones; § 19, Danville, Ketchum ; 

 § 20, Denuded granitic masses; § 21. Banded veins; Biddeford, Sher- 

 brooke ; § 22, Yeins at various N'ew England localities ; § 23, Mineral 

 species of these veins ; § 24, Veins in erupted granites ; § 25, Geodes in 

 granites ; § 26, Yeins distinguished from dykes ; § 27. Yolger and 

 Fournet on the origin of veins ; § 23, 29, Certain fissures and geodes 

 distinguished from veins opening to the surface; § 30, 31, Tempera- 

 tures of crystallization of granitic minerals. 



§ 1. The name of granite is employed to designate a supposed 

 eruptive or exotic nustratified composite rock, granular, crystal- 

 line in texture, and consisting essentially of orthoclase-feldspar 

 and quartz, with an admixture of mica, and frequently of a 

 triclinic feldspar, either oligoclase or albite. This is the definition 

 of granite given by most writers on lithology, and applies to a 

 great portion of what arc commonly called granitic rocks ; there 

 are, however, crystalline granite-like agregates in which the mica 

 is replaced by a dark colored hornblende or amphibole, and to 

 such a compound rock many authors have given the name of 

 syenite, while to those in which mica and hornblende co-exist, the 

 name of syenitic granite is applied. It is observed that in certain 

 of these hornblendic granites the quartz becomes less in amount 

 than in ordinary granites, and finally disappears altogether, giving 

 rise to a rock composed of orthoclase and hornblende only. To this 



* From the American Journal of Science for February and March, 1871 . 



