PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 31 
From Diorite. 
11. For long I had fruitlessly endeavoured to procure specimens such as 
could be analysed of the black mica which occurs throughout the dioritic rocks 
of Banffshire, in some localities sparsely, in others in large amount. 
In the summer of 1878, along with Mr Peyton, lately of Portsoy, I, how- 
ever, by the merest chance obtained, on the west shore of the Bay of the Durn, 
a large mass thereof, consisting of interplated crystals: it apparently formed 
a part of a vein ; it was attached to diorite, and passed somewhat into it. 
The colour was brown, somewhat bronzy ; the crystals, of about half an inch 
in size, were twisted among each other, and so had a glimmering, somewhat 
greasy lustre. Specific gravity 3° 074. 
On 1° 3 grammes— 
Silica, : : : 425 
‘From Alumina, . ‘ °018 
443 = 34°06 
Alumina, . ‘ : ih 39 
Ferric Oxide, . 5 2613 
Ferrous Oxide, . : ew el 
Manganous Oxide, . 384 
Lime, : oP 928 
Magnesia, . . 10°538 
Potash, . ; 6276 
Soda, : ‘ : preheat gs 
Water, . : . 4°052 
Loss in bath, * 217 per cent. 
12. The next specimens differ from the foregoing in containing more 
magnesia. They were obtained out of a granitic mass which lay on the south 
side of the road which runs along the side of Loch Stack, Sutherland. The 
mass lay towards the west end of the loch; it appeared to have fallen from 
the cliff on the north side of Ben Stack, but whether it was from an in- 
trusive vein or from a band of metamorphic segregation could not be ascer- 
tained ; it had much of the appearance of the former. 
It was in plates of some inches in size ; colour, brownish black ; greenish on 
being crushed ; lustre not very high. 
The only associates were the quartz and felspar of the granitic vein. Specific 
gravity, 3° 05. 
