Coleman — Nejpheline and other Syenites in Ontario. 153 



grains with equal diameters. These are on the average finer 

 grained than the Laurvikitic syenite, and may be divided into 

 leucocratic red syenites with comparatively little of the ferro- 

 magnesian minerals ; and melanocratic varieties containing 

 more than half dark minerals. It must be admitted that the 

 term leucocratic syenites is not happy for the less basic varie- 

 ties, since they are strong red and not white or pale colored. 

 Several specimens from east of Port Cold well are in reality 

 quartz syenite consisting of feldspar pegmatitically intergrown 

 with quartz, and small quantities of hornblende, augite, mag- 

 netite and apatite. The feldspars, which tend to be por- 

 phyritic, so far as their weathered condition permits one to 

 decide, are orthoclase, microcline and oligoclase. These rocks 

 seem to have the same composition as Brogger's nordmarkites, 

 though no mention is made of pegmatitic intergrowths in the 

 latter rocks."^ Aegirite has not been recognised in the rocks 

 from Port Coldwell, another point of distinction. 



The melanocratic syenites, consisting to the extent of at least 

 half of dark colored minerals, are dark gray rocks, usually with 

 a red tinge, not very coarse-grained, with about equal diam- 

 eters to the grains. The light colored minerals are ortho- 

 clase, some plagioclase and occasionally nepheline ; the dark 

 ones hornblende, pale blue-green augite and brown biotite in 

 not far from equal amounts : while magnetite and apatite are 

 always present, the latter often as numerous large prisms. 

 They appear by analogy to be related to the essexites. 



Plagioclase Bocks. 



Three kinds of plagioclase rocks accompany the syenites of the 

 Port Coldwell region, coarse-grained gabbro-like rocks older 

 than the syenite and penetrated or carried off as blocks by the 

 nepheline syenite ; fine-grained gray-brown rocks occurring as 

 dikes without well defined edges, in the nepheline syenite ; and 

 green-black dikes of diabase or diabase porphyrite, which are 

 latest of all. 



The gabbro is a speckled gray, coarse-textured rock showing 

 plates of mica and often a few porphyritic plates of plagioclase 

 megascopically. Thin sections are made up of half or less 

 than half of a plagioclase having the extinction angle of 

 andesine or sometimes labradorite ; of pale bluish green 

 augite, often idiomorphic, and brown biotite in about equal 

 amounts, while brown hornblende and olivine are in smaller 

 quantities. Magnetite and apatite in thick prisms are the chief 

 accessories ; and serpentine, chlorite and iron oxides occur 

 as secondary products. In one section the biotite surrounding 



*Ibid.,p. 55. 



