
PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 523 
lous ; infiltrated minerals, as an almost invariable rule, presenting themselves 
with a structure which exhibits bundles of fibro-crystalline radiations, which 
diverge or converge from the sinuosities of the drusy surface,according as i 
presents a convex or concave outline. 
The specific gravity of this hornblende is 3 : 375. 
1-3 grammes yielded— 
Silica, A . ° 502 
From Alumina, . abe 
WSs = 40-384 
Alumina, . é ~) 19.9012 
Ferric Oxide, . : o> B44 
Ferous Oxide, . : 2 ME 2 284. 
Manganous Oxide, . : * 461 
Lime, : ; ‘ . 11:°544 
Magnesia, , : a ge ans) 
Water, . ; d le dens 

99 - 482 
Insoluble silica, 1 +904 per cent. ; no visible impurity ; possible, unknown. 
Although I have no analysis to offer of it, there is still another variety to 
which I would direct attention. It is a mineral which occurs in a dyke at 
Crawford-John. Specimens of the rock were sent to me by GEIKIE as containing 
augite, to see if it were possible to extract therefrom a sufficiency for examina- 
tion. i 
Upon writing to Professor Grrxie that the mineral appeared to me to be 
hornblende, he stated that he had at first regarded the included dark mineral 
as being hornblende, but he now regarded it as augite, seeing that under the 
microscope it possessed all the characters of that substance. 
In separating chips for the measurement of the cleavage angle, I found it 
extremely difficult to obtain anything like a cleavage at all, from the presence 
of projecting points or rivets which interrupted the cleavage. On attempting 
to measure the angles of such imperfect cleavages as I did obtain, I was much 
puzzled at obtaining—in reflecting from cleavages in one zone—reflections at 
about the angles of 133°, 124°, and 87°; these are near the angles of augite 
in the first and last place, and of hornblende in the second. 
The fragments operated upon were not of a sufficiently satisfactory character 
to speak positively on the point; but, if I be right regarding them, we have 
here an illustration of what has been previously noticed both by G. Rose and 
HLAIDENGER. 
