THE MINERALOGY OF SCOTLAND. 433 
Hygroscopic Water, f . 694 
Heated barely red, lost, . , 5°688 of water, 
» bright red, , . 2°383 of oxygen. 
» white heat, A ; 3°138 more. 
These two analyses show that the “ London adventurers” were not alto- 
gether wrong in conceiving the mineral to be an ore of cobalt. 
From the old Workings of the Heegh-pirn Mine at Wanlockhead. 
This psilomelane was found by Mr. DupGEon and myself, among plates of 
grouped crystals of quartz, in a number of curved scales about the size of the 
nail, and three or four times its thickness. These curved scales stood upon 
their edges, as if they had coated some substance which had been afterwards 
dissolved away. They were of a brownish-black colour, and were soft-and dull 
on their outer surface. They were not much harder within. 
They were separated from quartz with much difficulty ; so that the insoluble 
matter is doubtless quartz. 
The speeimens had on their surface a little plumbo-calcite, vanadinite, and 
a trace of chrysocolla. 
The quantity of the mineral which could be gathered was too small for 
ascertaining the specific gravity. 
Manganous Oxide, . : =) (OF ot MinOsiin,O,. 
Oxygen, . : ‘ : ‘ : 9° 088 
Protoxide of Copper, ; ‘ ‘ "54 
Protoxide of Cobalt, : P ; “37 
Baryta, . ; : ; : ; 3°66 
Lime» . : ’ : . 228 
Magnesia, ; ; : : "012 
Potash, . : : i : : 4°088 
Soda, . _ : , 5 ‘ * 262 
Water, . : : : 5 ; 4-02 
Insoluble, p 2 : : : Dalat 
100-688 
I have lately, through the kindness of Dr. Witson of Wanlockhead, got 
much larger and finer specimens of psilomelane from the Leadhill mines. These 
are in botryoidal forms, though of a small size. Their fractured surface is blue- 
black and lustrous ; being thus less like wad than the above. 
A singular combination, apparently of wad and calcite, occurs at the Lead- 
hills. It is in masses of the size of an egg. The structure is like that of an 
onion ; the successive layers are about an eighth of an inch in thickness, and 
have the usual calcite cleavages. The inner layers are largely impregnated with 
