548 
Memorie del Reale Istituto Lombardo di Scienze Lettere ed Arti. 
Vol. VIII. Fasc. V. 4to. — From the same. 
Bulletin de l’Academie Imperiale des Sciences de St Petersbourg. 
Tom. III. Nos. 6-8. Tome IV. Nos. 1, 2. 4to, — From 
the Academy. 
Memoires de PAcademie Imperiale des Sciences de St Petersbourg. 
VII e . Serie. Tome III. Nos. 10—12. 4to. — From the same. 
Preisschriften gekront und berausgegeben von der fiirstlich .Tablo- 
nowskischen Gesellschaft zu Leipzig. Parts VIII. and X. 
1861. 8 vo. — From the same. 
Monday , 3 d March 1862. 
Dr CHRISTISON, V.P., in the Chair. 
1. On the Pressure Cavities in Topaz, Beryl, and Diamond, 
and their hearing on Geological Theories. By Sir David 
Brewster, K.II. 
In this paper the author gave a brief account of the various phe- 
nomena of fluid and gaseous cavities which he had discovered in 
diamond, topaz, beryl, and other minerals. He described — 
1. Cavities with two immiscible fluids, the most expansible of 
which has received the name of Brewstolyne , and the most dense 
that of Cryptolyne , from the American and French mineralogists. 
2. Cavities containing only one of these fluids. 
3. Cavities containing the two fluids, and also crystals of various 
primitive forms, some of which melt by heat and recrystallise in 
cooling. 
4. Cavities containing gas and vapour. 
The author stated that the first class of cavities existed in thou- 
sands, forming strata plane and curved, and intersecting one another 
at various angles, but having no relation to the primitive and second- 
ary planes of the crystal. From these facts he drew the conclusion 
that the minerals which contained them were of igneous origin ; and 
he considered this conclusion as demonstrated by the existence of 
what he calls pressure cavities , which are never found in crystals 
of aqueous origin. These microscopic cavities, which are numerous, 
in diamond, exist also in topaz and beryl. The gas which filled 
