Coleman — N ejpheline and other Syenites in Ontario. 151 



pale gray, and the hornblende prisms black, making a very 

 showy rock. In spite of the striking differences in appearance 

 of the varieties mentioned above, the range of minerals found 

 in the thin sections examined is not great, much less, for 

 instance, than in the nepheline rocks of Diingannon and York 

 branch in Eastern Ontario,"^ and none of the rarer minerals 

 have been found by myself, though zircon is mentioned in the 

 1863 report. The absence of muscovite, vscapolite, sodalite, 

 and of the usual microcline and microperthite is peculiar ; 

 though in some cases weathering has gone so far as perhaps to 

 obscure the structures of the feldspars. 



Augite Syenites. 



The other important group of rocks in the region includes 

 the augite syenites, which occur in two well marked varieties, 

 one dark browmish gray to black in color, coarse-grained and 

 with more or less of a plate-like character in the feldspars ; the 

 other red or reddish gray, finer grained and usually granitic 

 in texture. The first variety is much the more extensive of 

 the two and will be described first. 



In the dark variety, which is no doubt the trap that Logan 

 reports from the region, the feldspars are the prominent 

 ingredient, forming broad plates or narrow shining strips, 

 often Carlsbad twins, attracting the eye in the sun ; while the 

 relatively small amounts of ferro-magnesian minerals escape 

 notice. While dark brownish gray to black is the prevalent 

 color, there are phases of a dull brown or a dull red ; and 

 weathered glaciated surfaces may even be white by the bleach- 

 ing of the feldspar, when the augite and magnetite show as 

 angular or black filling material between the feldspar crystals, 

 which tend to be idiomorphic. 



The syenite is always coarse-grained, the crystals averaging 

 about a quarter of an inch in length, and also in breadth when 

 seen broadside, but often only a tenth of an inch in cross sec- 

 tion. There are coarse pegmatitic veins in the finer grained 

 rock having individuals of feldspar an inch or two in diameter, 

 and often fairly well built out in occasional cavities. 



As this rock has been quarried by the railway for bridge 

 construction, etc., it is easy to get fresh material. 



Thin sections consist of feldspar in more or less idiomorphic 

 forms with augite wedged in between, resembling, so far as one 

 can tell from a description, Brogger's laurvikite.f The 

 feldspars show no twin striations but have partly the appear- 

 ance of microperthite and partly of microcline. They are 



* See Bureau Mines, 1899, Corundum and Other Minerals, p. 205, etc. ; and 

 Corundiferous Nepheline Syenite, p. 250, etc. 



f Zeitschrift fiir Kryst. u. Min., Band 16, 1890, pp. 29, 30. 



