PROFESSOR. HEDDLE ON THE MINERALOGY OF SCOTLAND. 209 
ORTHOCLASE. 
Orthoclase from intrusion Veins,—Dykes. 
Dykes in Hornblendic G'neiss—1. From the great dyke of Ben Capval 
(K-haipeval), Harris. 
Quite a number of granite dykes are to be seen in the south end of Harris: 
towards the south-west these run nearly parallel to one another, cutting the 
strata at about right angles to their strike, and protruding from the inclosing 
rock like huge walls. Those of the south-east, or about Roneval, do not exhibit 
this parallelism, or general N.N.E. and 8.S.W. direction. 
The dyke of Ben Capval is markedly the largest of the series, and is the 
"grandest granite dyke in Scotland. Nearly two miles long, of about thirty feet 
in thickness, and protruding with a smooth and inaccessible front in some 
places to nearly an equal height above the surface, it forms quite a feature in 
the scenery, even when viewed from a distance. 
To the mineralogist this vein is interesting, as affording the largest, though 
perhaps hardly the finest, specimens of graphic granite to be obtained in Scotland; 
and also the most delicately-coloured specimens of rose quartz. Pale blue quartz, 
olive green muscovite, Haughtonite, magnetite, garnet, and crystalline yellowish 
green talc are also sparingly to be met with ; and white opaque beryll is said to 
have been found ; but this was searched for unavailingly both by Mr DupcEon 
and myself for the greater part of a day. In but one spot, where the rock 
_ begins to slope to the south, a blue felspar of unusual depth of colour was very 
' sparingly found. Its unusual colour led to.its being analysed. 
Colour, lavender blue. Specific gravity, 2°565; cleavage angle, 89° 50’ ; 
exhibits a structure to be afterwards noticed. 
Contact mineral, quartz ; visible Tn none. 
1°7105 grammes yielded— 

eiicaeer pes 1 O855 
From the alumina,. ‘024 
1 - 1095 — 64°86 
Alumina, h < . 18°469 
Ferric Oxide, . Z : ‘671 
Magnesia, . : 4 ‘71 
Potash, . : 4 . 12°98 
Soda, . ‘ ; sated Ocelot 
Water, . a ae *501 
; 100 - 086 
VOL. XXVIII. PART I. oo 
