202 Frofesaor T. G. Bonney — A Socialite Syenite 



sodalite, of which Professor Harrington gives an analysis, occurs in 

 streaks and irregular masses in the nepheline-syenite, the largest mass 

 measuring about 10 X 10 X 4 inches. These are traversed by a few- 

 little veins of a white and reddish felspar, which on analysis is found 

 to contain Kg O = 12-08 and Nag = 3-67, and thus to be a soda- 

 orthoclase. Small scales of dark-brown to black mica occur in the 

 sodalite. The constituents of the nepheline-syenite are plagioclase, 

 nepheline, and either brown mica or dark-green hornblende ; scapo- 

 lite and calcite are accessories, seldom absent but never abundant, 

 also sodalite, garnet, zircon, apatite, magnetite, and pyrite. Nepheline 

 is the most abundant constituent ; the plagioclase is albite, but with 

 a small proportion of lime ; the hornblende (probably rich in soda) 

 shows fairly good crystalline outlines and characteristic cleavage ;. 

 the calcite occurs like an original constituent, which is possible, a& 

 the rock is intrusive in limestone. 



The specimen from Hastings in the British Museum is very like 

 those brought by Mr. Whymper from the Ice Eiver. A similar rock 

 is found in boulders at Coburg on the north shore of Ontario. The 

 same collection contains blue sodalite in a generally similar rock 

 (with a vein of yellowish cancrinite) from Litchfield, Canada, as 

 well as in the familiar Ditroite of Ditro (Transylvania) and Miascite 

 from Miask in the Ilmen Mountains,^ at Thorstrand, near Laurvig, 

 and at Brevig, Norway, both of which have some resemblance to the 

 Ice River specimen. The interesting variety from Lake Baikal - 

 is massive, granular, and a rich dark-blue colour. A blue sodalite is 

 found less abundantly in a rather compact brownish-grey rock at tha 

 Montreal Reservoir and at Heidelberg near the same city. Here it 

 occurs in spots, which are often bordered by a white variety, and 

 suggest filled up cavities. Tbe mass of the rock is rather decomposed, 

 but felspar and nepheline with the general structure of a phonolite^ 

 can be recognized. Probably it would now be called a Tinguaite." 



Examination of slices cut from the Ice River Valley specimens- 

 shows the felspar to be imperfectly idiomorphic, with a slightly 

 ' dusty ' aspect, due to incipient decomposition. Most of it with 

 crossed nicols exhibits a composite structure, with a minute acicular 

 intergrowth or a colour mottling, the remainder having the twinning 

 of plagioclase, though even here the components are rather more 

 spicular in form and less sharply defined at the edges than is 

 usual.* They evidently represent the peculiar group — perthite, 

 soda-orthoclase, anorthoclase, and other plagioclases — so common 

 in rocks exceptionally rich in soda, such, for instance, as are figured 

 by Fouque & Levy ® in the well-known rocks from Miask and Ditro 

 and the elseolite-syenite from Brevig, except that I have not met 



1 As these rocks are practically identical, one of the names should be dropped. 



~ Described by Brogger and Backstrom : Zeitsch. Kryst., vol. xviii (1890), p. 222. 



3 For sodalite rocks in general see Rosenbusch, "Elemente der Gesteinlehre," 

 1898, pp. llo, 131. A most lucid description of the mineral sodalite is given by 

 Fouque & Levy, Mineral. Micrograph., 1879, pp. 447-450. 



* The extinction angles, measured from the composition edge, are rather small. . 



* Mineralogie Micrographique, pi. xlv, figs. 1 and 2. 



