so ROYAL SOCIETY OF CANADA 



ever, is not very striking on account of the small proportion of iron- 

 magnesia constituents which the rock contains. The foliated appearance 

 is accompanied by a streaked or schlieren structure in the rock, which 

 coincides with the strike of the foliation, that is with the direction of the 

 longer ajcis of the ridge. The streaks consist of portions of the rock, 

 which are coarser in grain than the normal rock or which contain some 

 constituents more abundantly developed. 



Under the microscope the rock is seen to be very fresh and to con- 

 sist of albite, microcline and nepheline, with which are associated in very 

 subordinate amount magnetite, biotite, hornblende, or very rarely 

 pyroxene. In some cases, but not usually, these two latter minerals oc- 

 cur together. Occasionally muscovite occurs associated with and par- 

 tially replacing the biotite. As accessory constituents garnet, scapo- 

 lite( ?) and zircon (?) were observed in very small amounts and each 

 in but a single specimen. The nepheline syenite in this township pre- 

 sents a variety which is highly feldspathic and rather poor in nepheline. 

 "^J'he feldspar is chiefly albite. This mineral is always well twinned 

 according to the albite law, and occasionally this mode of twinning is 

 combined with that according to the Carlsbad law. A series of measure- 

 ments of the extinction of this feldspar in sections in the zone of the 

 macropinacoid were made in slides of the rock from the highest point of 

 the Blue mountain, and it was found that the maximum extinction on 

 either side of the twinning line was 16°. A separation of the consti- 

 tuents by Thoulet's solution showed the feldspar to have a specific gravity 

 of very nearly 2.60. The feldspar is therefore albite. Similar separa- 

 tions carried out on specimens collected on lot 18, con. VI and on 

 specimens of the various varietal differentiation products of the rock to 

 be mentioned below, show that the plagioclase present in the rock is al- 

 ways albite and that no feldspar more basic than this specimen (that is, 

 having a specific gravity greater than 2.60) occurs in the rock. 



The microcline is much less abundant than the albite, although it 

 always occurs in considerable amount. There is, as a rule, from two to 

 four times as much albite as microcline present. The nepheline is 

 usually quite fresh, but occasionally shows traces of alteration. It oc- 

 curs in large, irregular shaped grains. It is on the whole about equal 

 to the microcline in amount, but locally becomes the preponderating 

 constituent in the rock. The biotite is a very strongly pleochroic variety. 

 a = dark greenish brown, nearly black. C = pale yellow. Ab- 

 sorption a > C. The axial angle is very small. The hornblende is 

 hastingsite. The small individuals possess a fairly good crystalline 

 form, but the larger are irregular in shape, sometimes lying between the 



