134 J. J. H. TEALL ON THE METAMORPHOSIS OF 



granular rock of true igneous character * ; the other a typical 

 hornblende-schist. These two varieties shade into each other by 

 the most imperceptible gradations. The distribution of the two 

 varieties throughout the dykes is somewhat irregular. In many 

 places and for considerable distances no trace of foliation can be 

 detected, in others the whole mass of the dyke is foliated. The 

 prevalent strike of the foliation in the district lying to the south- 

 east of the hill overlooking the lake is nearl}^ at right angles to the 

 course of the dykes, and therefore parallel with the strike of the 

 prevalent gneissic banding. 



In some places the distribution of the foliated and no n- foliated 

 varieties is extremely irregular and quite independent of the course 

 of the dyke ; at others it exhibits a marked tendency to bend round 

 so as to become parallel with the margins. This latter feature is 

 especially developed at certain points where the gneiss and dyke 

 become very intimately blended along the junction-planes, owing to 

 the extension of tongues and flame-like processes of the dyke into 

 the gneiss. At these points there is often perfect parallelism between 

 the foliation of the gneiss and dyke, and it is possible to obtain 

 hand specimens in which the rock of the dyke is represented by a 

 band of hornblende-schist in the gneiss. 



The jointing of the dyke is often very irregular, the planes 

 appearing bent and twisted. This may be well seen at the small 

 beach on the north side of Scourie Bay. Veins of quartz traverse 

 the dyke in certain places, and at the small beach above referred 

 to a vein of nearly pure felspar occurs. The surface of the felspar 

 is weathered, but the main mass is very fresh. One cleavage is 

 strongly marked, so that the mineral has a platy structure. Twin- 

 striation is not, as a rule, recognizable ; but Dr. Trechmann tells me 

 that the principal cleavage is parallel to the brachypinacoid, and 

 that would account for it. In one case I have observed twin-striation 

 on a cleavage-face. To determine the specific gravity, seven small 

 grains of the pure felspar substance were selected. In a Sonstadfc 

 solution having a sp. gr. of 2-638, two rose, one remained suspended, 

 and four sank. In a solution the sp. gr. of which was 2*644, 

 three rose, one remained suspended, and three sank ; and in one, the 

 sp. gr. of which was 2*654, three rose, and four remained suspended. 

 The specific-gravity determinations therefore indicate andesine, and. 

 this is confirmed by the following analysis : — 



* A dyke having the same strike and composed of a rock precisely 

 similar to the one here referred to occurs on the N.E. shore of Loch Glen 

 Coul. The water of the lake is in contact with the dyke for some distance. 

 If the Scourie dykes were continued towards the S.E. in the same straight 

 line they would pass a mile or two to the N.B. of the Grlen-Coul dyke. 



