486 Canadian Record of Science. 



A number of dykes which occur near the west bank of 

 the Rideau canal, in the vicinity of Seeley's Bay, were 

 •examined. One of the smaller of these, which cuts the 

 •graphite-holding crystalline limestone near a narrows in 

 the canal, has a width of four feet, and sends off branches 

 into the surrounding rock. It is dark in colour, very 

 fine-grained, and possesses a highly perfect columnar 

 structure, developed in a direction at right angles to its 

 walls. The rock has a specific gravity of 2*92, and on 

 analysis was found to have the following chemical com- 

 position : — 



Si0 2 46.51, Ti0 2 2.90, A1 2 3 12.33, Fe 2 11.14, Fe 2 3 3.87, 

 CaO 9.37, MgO 6.48, Na 2 3.67, K 2 1.18, H 2 + C0 2 2.47, 

 S '16. Traces of copper and barium were observed. Man- 

 ganese and nickel are both present. 



The rock fuses readily. About twelve ounces of it 

 were finely pulverized, placed in a covered graphite cruci- 

 ble, and fused for some hours in a coal furnace. It was 

 then allowed to cool. On breaking the crucible the fused 

 mass was found to have separated into two parts — a highly 

 perfect, clear, slightly amythistine glass, and a " button " 

 containing most of the metallic matter. The latter rested 

 •on the bottom of the crucible, and was easily detached 

 from the glass. It had a diameter of about 2'5 cm. and 

 a thickness of about 1 cm., and weighed about one and 

 one-quarter ounces. 



In hand specimens many minute crystals are seen scat- 

 tered through the rock. Examined microscopically, in 

 thin sections, the groundmass is found to be very fine- 

 grained, and, in the denser portions, microlitic. Abundant 

 phenocrysts of plagioclase and pyroxene are present. 

 These minerals are also constituents of the groundmass, 

 which contains, in addition, much magnetite. The 

 larger individuals of plagioclase of the groundmass, Fig. 

 .2 (In), are in needle or lath-like forms, having an average 

 length of about 0*05 mm., but there are innumerable 



