12 F. D. Adams — Nepheline Syenite in Ontario. 



some cases present in large amount, are scapolite and calcite, 

 and as less important and less abundant accessory constituents 

 are garnet, zircon, sodalite, magnetite, pyrite and apatite. 

 These latter, with the exception of garnet, always occur in 

 very subordinate amount. Two or three other minerals occur 

 in small amount in individual slides, or can be seen on the 

 weathered surface of certain specimens, as these however could 

 not be determined with certainty, without prolonged investiga- 

 tion their true nature is as yet doubtful. 



The rock is usually very fresh and has a true hypidiomorphic 

 granular structure. Evidences of pressure are in most cases 

 entirely wanting. In a few slides however slight strain 

 shadows and bending of twin lines are to be observed, and in 

 one specimen distinct cataclastic structure was seen. 



Nepheline. — This is by far the most abundant of all the 

 constituents of the rock. It always forms the greater part of 

 the rock and in many places, over considerable areas, the rock 

 is composed of this mineral associated with a little mica or 

 hornblende. The mineral is clear and colorless and is usually 

 free from inclusions. It has a low double refraction and paral- 

 lel extinction. On basal sections it is seen to be uniaxial and 

 negative. It is easily etched by hydrochloric acid in the thin 

 sections and can then be stained with fuchsine. In a few 

 cases it was observed to be altered to muscovite. In hand 

 specimens the mineral is seen to possess a luster which is 

 vitreous rather than oily, so that it has been referred to as 

 nepheline rather than as eleolite. An analysis of it is given 

 by Dr. B. J. Harrington in the accompanying paper. 



Plagioclase. — The rock contains no primary orthoclase, but 

 feldspar though seldom very abundant is in most cases present, 

 often in considerable amount. It is twinned polysynthetically, 

 the bands being usually narrow and often indistinct. When 

 cut at right angles to an optic axis it is seen to be biaxial. Its 

 specific gravity, determined on two fragments taken from the 

 very coarse grained variety of the rock at the York River, is 

 2*6207 and 2*625, while in a separation of the constituents of 

 a specimen of the rock from lot 25 of range XIV of Dun- 

 gannon, it was found to have a specific gravity of not over 

 2*623. The extinction on either side of the twinning line, 

 measured on a cleavage fragment from the York River was 

 2-J . These facts prove it to be an albite, with probably a 

 very small percentage of lime. 



Mica. — This constitutes the iron-magnesia constituent of the 

 rock in three out of the five localities from which specimens 

 were examined. In these cases it occurs alone, while in the 

 other localities where hornblende is present the mica is absent. 

 It is nearly black when seen in the hand specimens and in the 



