[ADAMS A barlow] ALKALI SYENITES OF EASTERN ONTARIO 4S 



con. II, have this coarse pegmatitic development and consist of albite, 

 nepheline and black mica. Their exact mode of occurrence cannot in 

 all cases be seen on account of the drift which surrounds them, but on 

 the north half of lot 32, con. Ill, this same development of the rock is 

 seen cutting the limestone in the form of great dykes; while on lot 32, 

 con. II, it is seen in dykes of the same character, penetrating the gabhro 

 and cutting abruptly across the course of its foliation. These dykes on 

 lot 32, con. Ill, hold included masses of limestone, very coarse in grain, 

 crystals of zircon, dark reddish brown in colour, over an inch in dia- 

 meter and each consisting of a double tetragonal pyramid, were also 

 found in these dykes, as well as crystals of apatite. 



The dykes on lot 32, con. 11, in some cases become extremely coarse 

 in grain. A specimen obtained from one of them consisted of a pyra- 

 midal mass of nearly pure nepheline, which measured 14 inches on the 

 side and was composed of individuals of this mineral from three to^ five 

 inches in diameter. The nepheline is in places slightly streaked with 

 sodalite, and on the weathered surface shows in places irregular-shaped 

 cavities which represent spaces from which masses of calcite have been 

 dissolved. 



An important area of nepheline syenite is that which runs across 

 con IV, from lot 27 to lot 32. It is very well exposed on lot 30, con. IV, 

 on the property of Mr. Archibald McOoll. The greater part of this 

 mass consists of a light grey, well foliated nepheline syenite, containing 

 a hornblende resembling hastingsite. A specimen of this rock, which 

 was examined microscopically, was found to be composed of microcline, 

 albite, nepheline and hastingsite, with a little microperthite. Both 

 microcline and albite are present in large amount. Inclusions of the 

 former were observed in the nepheline. The rock is quite fresh and 

 has the almost allotriomorphic structure usually seen in these foliated 

 nepheline syenites. In addition to this, which may be called the normal 

 development of the rock, there are on the same lot other varieties. One 

 of these is a very coarse pegmatitic phase of the rock like that forming 

 dykes on lot 32, con. II, but even coarser in grain. One exposure of 

 this is seen not far from Mr. McColl's house and has been opened up by 

 blasting. Here the rock consists essentially of nepheline and albite, 

 with occasional individuals or small masses of coarsely crystalline cal- 

 cite. The iron-magnesia constituents are present in very small amount, 

 and are over large surfaces entirely absent. They are represented chiefly 

 by a black mica. A black hornblende, probably hastingsite, as well as a 

 white mica and a little pyrrhotite were also observed. The rock con- 

 tains masses of pure nepheline as much as a yard in diameter. 



