[AbAMS 4 BARLOW] ALK ALT SYENITES OF EASTERN ONTARIO SI 



feldspathic elements of the rock and sometimes enclosing them. It has 

 an intense colour and a very strong pleochroism, as follows : — 



a = green with yellowish tinge, h = deep green with bluish 

 tinge. C = deep green. The absorption is C ~ h > a. The dispersion 

 is very strong and sections at right angles to the optic axes are nearly 

 opaque. The extinction is high, probably about 30°. The magnetite 

 occurs chiefly in large individuals scattered sparingly through the rock 

 and usually possessing a rude crystalline form. The garnet, which was 

 found in small amount in one specimen of the rock holding hornblende, 

 is pale yellowish brown in colour and identical in all its characters with 

 that occurring associated with the hastingsite in the Dungannon nephe- 

 line syenite from which the latter mineral was originally described. (^) 



As has been mentioned, the rock often possesses a streaked or 

 schlieren structure. The more coarsely crystalline streaks are usually 

 composed of albite and nepheline — individuals of the latter mineral 

 seven inches in diameter having been observed in one case. Sodalite 

 was observed in association with this coarsely crystalline nepheline in 

 a few places. 



The rock has a granular texture with which the faint gneissic and 

 the schlieren structures are combined — blocks of the rock thus resembling 

 a somewhat impure crystalline limestone or marble. Under the micros- 

 cope the structure is seen to be essentially allotriomorphic. In one case 

 a minutely miarolitic structure was observed. 



A fine development of the nepheline syenite is seen forming high 

 white cliffs at the western end of Mountain Lake, on the north side of 

 the lake, on lots 13 and 14, con. X of Methuen. The rock consists of 

 about one-third nepheline and two-thirds feldspar and is almost free from 

 iron-magnesia constituents. 



In a rather more micaceous specimen of the nepheline syenite from 

 the Blue Mountain, a short distance further east, on lot 15, con. IX of 

 Methuen, a small quantity of spinel in little rounded individuals was 

 observed in the thin sections. The occurrence of this mineral is of in- 

 terest in showing that the magma here contained a slight excess of 

 alumina, which separated in combination with magnesia as spinel, while, 

 as mentioned below, the much larger excess of alumina in other parts 

 of the mass separates out as corundum. 



The White Alkali Syenite. — >The nepheline syenite in places be- 

 comes rather fine in grain and poorer in nepheline, passing into a white 

 syenite. 



' Adams, F. D. and Harrington, B. J. — On a new alkali Hornblende and a 

 titaniferous Andradite from the Nepheline Syenite of Dung-annon, Hastings 

 County, Ontario. — Am. Jr. of Science, March, 1896. 



