571 
of Edinburgh, Session 1865-66. 
effervesce with mineral acids, and contain the following ingredients 
proportionally in the order in which the}'- are written : — Alumina, 
Silica, Lime, Magnesia, Oxide of Iron, and a trace of Manganese. 
The black coating on many of these stones, which is too minute 
for analysis, and which may be easily removed, is very remarkable. 
If it is not carbonaceous it must be an aluminous deposit, when the 
particles of the aluminous solution have become so small as to be 
unable to reflect liglit. This supposition will not appear unreason- 
able to those who have seen the surfaces of fracture of certain 
specimens of quartz, where the separated fibres are so minute as 
to be incapable of reflecting the lowest order of tints in Newton’s 
scale. The specimen of quartz in which I observed this very 
remarkable phenomenon was, I believe, exhibited to the Society. 
Mr Haidinger afterwards found a less perfect specimen in which 
the^ surfaces of fracture were equally black. 
The following Gentlemen were admitted Fellows of the 
Society : — 
John M‘Nair, Esq. 
Professoe Spence. 
Thomas Nelson, Esq, 
The following Donations to the Library were announced : — 
Transactions of the Koyal Scottish Society of Arts. Vol. VII. 
Part 1. 8 VO . — From the Society. 
Philosophical Transactions of the Koyal Society of London. Vol. 
CLV. Part 2. London, 1865. 4to. — From the Society. 
Proceedings of the Koyal Society of London. Vol. XV. No. 80. 
8 VO . — From the Society. 
List of the Koyal Society of London, 30th Nov. 1865. 4to. — 
From the Society. 
Sketch of the History of the High Constables of Edinburgh. Ky 
James Marwick, F.K.S.E, Edinburgh, 1865. 8vo. — From 
Charles Lawson, Esq. 
Journal of the Koyal Horticultural Society of London. New Series. 
Vol. I. Part 1. 8vo. — From the Society. 
Proceedings of the Koyal Horticultural Society of London. Vol. 
V. No. 9. 8 VO . — From the Society. 
