PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 23 
In the ascertaining the percentage of water, it was found that the heat of 
the Bunsen produced no change of colour or of molecular state ; the heat of 
the blast, however, caused some agglutination. 
1° 499 grammes lost ‘022 in water-bath ; over the Bunsen for two hours, 
lost -0238; over the blast for a quarter of an hour, 0318. The water is, 
therefore, retained with extreme tenacity. 
2. From the great vein of Ben Capval. 
Though this vein and those parallel to it, which cut the strata on the 
south shore of Harris between the Toehead promontory and Huishinish House, 
afford this mica, it occurs in these north and south veins in such very small 
quantities as to constitute a marked point of distinction between them and 
the radiating veins which intersect Roneval and the adjacent country. 
Towards its northern extremity, the Capval vein afforded a sufficiency for 
analysis. The crystals here are of only an inch or two in size, elongated 
and diverging, jet black, rarely slightly rusty. They are biaxial to a small 
extent. 
Their specific gravity is 3° 071. 
25 grains yielded— 
Silica, : . : . 36°806 
Alumina, . y, ens 22 
Ferric Oxide, . : oe Gl 
Ferrous Oxide, . : > 2£i* 308 
Manganous Oxide, . : bas 
Lime, 1°54 
Magnesia, : . 8:°784 
Potash; ~. : J who ce 
Soda, 1: 342 
Water, 2°47 
100 - 396 
Possible impurity unknown. 
3. From Loch Roag, Lewis. 
The road which passes along the north shore of Loch Roag skirts a small 
fresh-water lake called Loch-na-Muilne. 
Granitic veins cut the gneiss on its northern banks, and in these and in 
similar veins in the cliffs, and in the highest knoll which is to be seen to the 
north-west, the mineral is to be found in plates of an inch or two in size. I is 
associated with pinkish orthoclase, pale blue oligoclase, fatty quartz, and occa- 
sionally hornblende. Its colour is dark brown to black. 
