

210 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
11°52 per cent. of the silica were insoluble in a boiling solution of sodium 
carbonate. 
Possible impurity, quartz. 
2. From a great dyke which protrudes from the steep shore slope facing the 
rock of Stromay, in the Sound of Harris. 
This dyke, though of much greater thickness than the last, is not nearly sc So 
rich in minerals ; it is mentioned in the 3d vol. of the ‘“‘ Edinburgh Philosophical 
Journal,” as containing “moonstone”; besides this, it contains Haughtonite, 
- and fine specimens of graphic granite, of which the felspar is, in MAccuLLocuH’s 
words, “ white, translucent, and nacreous,—acquiring, after exposure, an argen- 
tine brilliancy.” It likewise contains imbedded crystalline masses of orthoclase 
of wondrous purity of appearance, somewhat foliated in structure. | 
Pellucid, almost transparent ; but with fibrous-looking portions which are 
opaque or brilliantly lustrous, according to the direction in which they are 
viewed ; this structure will be particularly noticed below. 
Colour, gray. Lustre, somewhat vitreous, but brilliant. S. G., 2°574. 
Cleavage angle, 89° 55’, 
Contact mineral, the graphic felspar. Visible impurity, none. 
1°633 grammes yielded— 

Silica, . ; 2 . 1 +0568 
From Alumina, : x  OUOS 
1067 = 65346 
Alumina, . So) Areas 
Ferric Oxide, 4 92 
Lime, ; d ‘ ‘68 
Magnesia, . : : 253 
Potash +. : al eel orisie 
Soda, . ; ; s. oe 505 
Water, : ‘ : °18 
100 - 694 
Possible impurity, unknown. 
From Dykes in Mica Slate. 
3. Ata turn of the road, which leads up Glen Fernate, in Perthshire, on 
the east side of the stream, just where a bend is made to the west about two — 
