COMPOSITION OF THE FELDSPARS. 35 



quartz trachytes,* and later to the liparites or rhyolites,t which now 

 include most of the quartz trachytes of the older authors. Bunsen, indeed, 

 maintained both before and after 1853, that baulite was a mechanical mix- 

 ture — a rock, and not a mineral. | 



In 1854 Dr. T. Sterry Hunt stated that the triclinic feldspars constituted 

 a genus, of which albite might be taken as one representative, and anor- 

 thite as the other. The intermediate feldspars might be distinct species, or 

 they might be looked upon as variable mechanical mixtures of the two typi- 

 cal feldspars, albite and anorthite. A similar mixture of albite with a potash 

 feldspar, and anorthite with a soda or magnesian one, as well as of orthoclase 

 with a lime or potash feldspar, were regarded as probable. Hunt distinctly 

 objects to any idea that these variable feldspars were formed by chemical 

 miions between the diflerent types, and makes it clear that he had in mind 

 the process of envelopment and variable, mechanical, contemporaneous 

 intercrystallization, on which he founded his doctrines of the origin of 

 crystalline rocks, pseudomorphism, and metamorphism. In this he fol- 

 lowed Scheerer's views regarding the relations of iolite and aspasiolite, 

 and of olivine and serpentine. The proportions of these intermixtures of 

 the feldspars wei'e regarded by Hunt as entirely variable and indefinite, 

 being " such mixtures of species as constantly take place in the crystalliza- 

 tion of homoeomorphous salts from mixed solutions," and he explained the 

 process in every case in the same way as he did in the case of perthite. 

 That this view of the mixture of the feldspars is the same as his explana- 

 tion of pseudomorjihism can be seen from his statement that the latter has 

 resulted in many instances from the association and crystallizing together 

 of homologous and isomorphous species. § 



In 1864 Professor Gustav Tschermak advanced the theory that (excepting 

 hyalophane and danburite) there were three distinct species of feldspar: 

 Orthoclase, or potash feldspar; Albite, or soda feldspar; and Anorthite, or 

 lime feldspar. He held that soda and potash were not isomorphous, and 

 therefore all orthoclase crystals containing soda were mechanical mixtures 



• Zivkel, Sitz. Wien. Akad., 1863, xlvii. (1) pp. 243, 244; Lelirbuch der Pctrograpliie, 1SG6, i. 25; 

 ii. 154-166. 



f Zii'kel Die mikroskopische Bescliaffenlieit der Mhieralien uud Gesteiiie, 1S73, p. 341. 



X Bunsen Aim. Physik Chemie, 1851, Ixxxiii. 199, 201 ; Auu. Cliemie Pharm. 1854, Ixxxix, 98; Preyer 

 uud Zirkel, Reise uaek Island im Souinicr, ISGO ; pp. 317-324. 



§ Proc. Am. Assoc. Adv. Sci., 1854, viii. 237-547 ; 1871, xx. 1-59 ; Am. Jour. Sci., 1853 (2), xvi. 218 ; 

 1854, xviii. 270, 271 ; Pliil Mag., 1855 (4), ix. 354-363 ; Geological Survey of Canada, Report of Progress, 

 1853-1856, pp. 373-383 ; 1858, p. ISO ; Canada iu the London luteruatioual Exliibilion, 1862, p. 65 ; Geology 

 of Canada, 1863, p. 4S0. 



