[ADAMS & barlow] ALKALI SYENITES OF EASTERN ONTARIO 29 



the gneissic granite of the district. Much of the rock contains over 

 ten per cent of corundum.^ 



II. The Nepheline and associated AlJcali syenites of the tovjn- 

 ship of Monmouth. — The largest and most important occurrence of 

 nepheline syenite in this township, is that which is found as a border 

 around the body of pegmatitic granite which runs through the centre 

 of the township stretching in a direction about N.30°E. from con. VII 

 to con. XIV, a distance of about six miles. This granite mass has a 

 maximum width of a little over a mile. The border of nepheline syen- 

 ite varies from one-eighth to half a mile in width. Fine transverse 

 sections from the limestones on either side through the nepheline border 

 to the central mass of granite can be obtained on the several roads which 

 cross this occurrence. 



The rock which has been referred to as granite, is pink or red in 

 colour and is usually of medium grain. It shows in many places that 

 irregular and often rapid variation in size of grain which is seen in 

 pegmatite. At the north-eastern end of the mass on lot 29, con. XIII, it 

 has a distinctly foliated structure. Farther south the foliation becomes 

 less distinct, although the rock still retains a streaked appearance. 



This granite is never rich in quartz, although in the north-eastern 

 part of the mass and as far south as con. XI, this mineral is present 

 in considerable amount. Farther to the south-east the quartz decreases 

 in quantity and the rock passes into a syenitic phase. The rock as ex- 

 posed on lot 26, con. XII of Monmouth, in the middle of the granite 

 mass, is a medium grained granite, red m colour and with a rude folia- 

 tion. The quartz is light gray and glassy. The feldspar is red on the 

 fresh surface of fracture and shows a good cleavage and high lustre, but 

 weathers to a pale red or pink colour. The iron-magnesian constituent 

 is present only in small amount. Under the microscope the rock is 

 seen to be composed of the following minerals : — albite, microcline, ortho- 

 clase, microperthite, quartz, hornblende, biotite, sphene, apatite and 

 magnetite, lit was found by making a separation with Thoulet's solu- 

 tion that the amount of albite and microperthite taken together was 

 about double the sum of the amounts of orthoclase and microcline pre- 

 sent in the rock. Quartz is about equal in amount to the potash feld- 

 spars. The ferro-magnesian constituents occur in aggregates of in- 

 dividuals which have a rather frayed or irregular outline. Very few 

 of these approach an idiomorphic development. Two varieties of horn- 

 blende are present : one green and the other blue in colour. The former 

 is evidently ordinary hornblende, showing a pleochroism in yellow and 

 green tints with an extinction of 20°. The blue variety of hornblende 



^ Geological Survey of Canada, Summary Report, 1905, p. 93. 



