48 ROYAL SOCIETY OF CANADA 



the boundary. The occurrenei', tlierefore, probably lies partly in Fara- 

 day and partly in Wollaston. Its position, however, is here taken as 

 lot 9 of con. XVI of Wollaston. The mass is peculiarly situated, form- 

 ing as it does a solitary exposure only twenty feet across, surrounded by 

 gabbro diorite. (') The nepheline syenite has a more or less well marked 

 banded character and is usually coarse in grain. The relative abundance 

 of the constituents varies more or less in différent parts of the mass. 



Under the microscope the rock is seen to consist essentially of nephe- 

 line, plagioclase and biotite, wiiile microcline, calcite, magnetite, pyrite, 

 apatite and zircon (?) occur as accessory constituents. The biotite 

 usually occurs in rather large irregular-shaped individuals which are 

 strongly pleochroic in colours, ranging from a pale yellow to a very deep 

 brown, basal sections being nearly black. It is sometimes found ad- 

 joining or partially surrounded by magnetite or chlorite, this latter 

 mineral clearly showing its derivation from the biotite. The plates of 

 biotite are frequently twisted. The prevailing feldspar is an albite, 

 which, with the nepheline, in some places makes up the entire rock. As 

 a rule it is fresh, occurring as large individuals and smaller grains, often 

 showing fine polysynthetic twinning, the lamellœ being distinctly bent in 

 some cases and the mineral often showing strain shadows. Microcline 

 is present in small amount and microperthite intergrowths are common. 

 The nepheline forms large irregular individuals, frequently cracked and 

 very turbid, this turbidity being due to incipient decomposition. In- 

 clusions of small rounded grains of plagioclase and untwinned feldspar, 

 as well as of calcite and biotite, are frequently found in the nepheline. 

 Calcite is always present and is often abundant, occurring in large in- 

 dividuals. The shape of the grains indicates that it is derived from 

 limestone inclusions. The twinning lines of the calcite are often curved 

 in a striking manner. Both magnetite and pyrite occur in small 

 amounts, the former being much more abundant. The pyrite in one or 

 two cases is found partially altered to hematite, while magnetite forms 

 a border around it. Little zircons (?) and a few grains of apatite pos- 

 sessing good crystallographic outlines are present in the sections. The 

 curved individuals of biotite, plagioclase and calcite, and strain shadows, 

 suggest that the rock has been subjected to great pressure. 



A separation of the constituents of the rock was made by means of 

 Thoulet's solution, which showed that the feldspar present was almost 

 exclusively al])ite, the potash feldspar present being quite subordinate 

 in amount but Avhite in colour like the albite, and thus not to 



' A somewhat similar occurrence has been described by Ransome in the 

 case of a nepheline syenite at Brockville, N.J., Am. Jour, of Sci., 1899, p. 426. 



