PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 17 
4, From granular limestone at Glen Beg, Glen Elg. 
At about one-fourth of a mile to the north-east of the hamlet of Balvraid, 
the limestone contains Biotite (in association with the hydrated labradorite— 
noticed in Chap. II. of this series), necronite, and balvraidite. 
The mineral is generally immediately in association with the balvraidite. 
Its colour is rich chocolate brown, its lustre brilliant. 
1°28 grammes yielded— 
‘Silica, . : : . 39°46 
Alumina, . : : 5 MUG O25 
Ferric Oxide, ; ; , Tao 
Ferrous Oxide, . , 5 dls: 
Manganous Oxide, . : "53 
Lime, . ; 4 : a ll Obst, 
Magnesia, . : : Ae 
Potash, : ; F A AGBED2 
Soda, . * 26 
Fluorine, . F 3 P “32 
Water, k ‘ ; f2 a 04 
99°56 
Possible impurity, balvraidite. 
From Hornblendic and Serpentinous Rocks. 
5. Hornblendic gneiss, highly contorted and fractured, occurs in the pen- 
insula of Hillswick, in Shetland. 
At the point called the banks (7.¢., shores) of Nudista, a bed—simulating a 
vein of precious serpentine—protrudes, just north of the spot where these 
“banks ” rise into rocky cliffs. 
This bed is in contact on the south with one of matted anthophyllite ; while 
it carries, partly in its centre and partly on the side opposite to the antho- 
phyllite, another consisting of actynolite with a matrix of snow-white talc; 
this latter, in passing shorewards, loses the actynolite, and gradually merges 
into a soft talc-chlorite, as it reaches and passes beneath high-water mark. 
Just about this point a considerable portion of the bed—here almost pulpy 
from absorbed water—consists of Biotite. 
It is in a very loose and incoherent state, much resembling a friable talc. 
Its colour is bronzy brown ; it is translucent in thin fragments. 
The scales fall asunder in water, so that the specific gravity could not be 
determined. 
1657 grammes gave-— 
VOL. XXIX. PART I. E 
