PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 533 
studding a kind of pale-green paste, much resembling serpentine ; and this 
paste would seem to pass by insensible gradations into the subfibrous mineral, 
of which the above is the analysis. 
So that it may be the correct view to regard this as being a transmutation from 
labradorite in the first place. 
Here, then, as in the more easterly bed, we have to call in the actual trans- 
mutation by magnesian waters ; and as portions of this transmuted material are 
distinctly fibrous, we have to ask ourselves if, as a preliminary stage in the 
process, the labradorite had been, through the insertion of magnesia, converted 
into a fibrous hornblende. Such a change Biscuor considers possible ; but it 
has to be remarked, that while the possibility of the increment of magnesia 
must be granted, it is not easy to account for the simultaneous removal of the 
alumina. 
28. For an illustration of the increased abstraction of the silica, we will go 
to Pundy Geo, near Fethaland, in the mainland of Shetland. 
Here a picrolitic mineral is to be found in large, coarse, fibrous masses with 
a columnar appearance. ‘The form is that of actynolite ; the rough crystals are 
several inches in length, and of a third of an inch in breadth. The colour is 
dark green. The specific gravity 2°65. 
On 1°314 grammes— 
Silica, . 3 : 5115} 095) 
From Alumina, . -008 
Byrd) = 42-932 
Alumina, . : : eel eo 4ug 
Ferric Oxide, . : a He IOS 
Manganous Oxide, . ; *419 
Lime, : : , 2 °8 
Magnesia, . : : . 86°195 
Potash, . 3 : : ‘81 
Soda, ‘ : ‘ ; -366 
Water, ; : ; a le 

99-973 
Absorbs 1°217 per cent. of water; insoluble silica, 4°378 per cent. Here 
the change into serpentine—a ferruginous serpentine—is well-nigh perfect. 
There can be no doubt that the mineral changed is actynolite. Associated 
minerals here are chlorite, with imbedded simple and twin crystals of blue- 
black magnetite, the finest in Scotland. 
29. There is a mineral obtained in Ayrshire (the locality I cannot give—my 
specimens were purchased from the dealer, Parrick Doran) which has passed 
VOL. XXVIII. PART II. 6 Y 
