
254 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
Insoluble silica 12°58 per cent. ; possible impurity, augite. 
Mr DvunpceEon has a specimen of the Cuchullin diabase from the east slope 
of Scuir-na-Gillean, in which the labradorite is of the colour of the last analysed, 
but which has iridescent reflections which are fairly brilliant in colour. 
From Diorite. 
4, On the north side of Glen Bucket a dyke of diorite (2), with gigantic 
crystals of jet black hornblende imbedded in snow-while labradorite, appears in 
the low flanks of Craig-an-Innean, striking in the line of Tullocharroch. 
The associated minerals are ilmenite, Biotite, apatite, sphene, ripidolite or 
chlorite, and very rarely a rose-coloured felspar in crystals—the last five being 
rare. 
The labradorite is in confused crystalline granules; instead of being tough, as 
this mineral usually is, it is brittle ; its specific gravity is 2-674. 
11°53 grammes yielded— 

Silica, ~ ‘ ‘7665 
From Alumina, . -008 
7745 = 50°588 
Alumina, . : ; . 28°34 
Ferric Oxide, . : SE SrO5 
Magnesia, ; ; : * 588 
Lime, : : : ae de TA 
Potash, .. , : ge te 
’ Soda, P ; ; <2 008 
Water, © Se et ay 

99°892 
10 «25 per cent. of this silica insoluble ; possible impurity unknown. 
The associated mineral is named hornblende, both from cleavage angle and 
analysis ; according to Rotu, labradorite and hornblende exclude each other ; 
it is here not so. The rock is a diorite, having labradorite as the felspar. 
From Gabbro. ~ 
5. The great mass of this rock in Unst, in Shetland, terminates about the © 
north of the island of Balta. On the south side of Brough Geo, in that island, 
two pseudo veins are to be seen protruding through the turf, and striking over 
the edge of the cliff. The one consists of a paste of granular labradorite, carry- 

