64 
show that ruby, sapphire, spinel, and emerald were formed at a moderately 
high temperature, under so greaV a pressure that water might be present 
in a liquid state, The whole structure of diamond is so peculiar that it can 
scarcely be looked upon as positive evidence of a high temperature, though, 
not at all opposed to that supposition. The absence of fluid-cavities con- 
taining water or a saline solution does not by any means prove that water 
was entirely absent, because the fact of its becoming inclosed in crystals 
depends so much on their nature. At the same time the occurrence of 
fluid-cavities containing what seems to be merely liquid carbonic acid is 
scarcely reconcilable with the presence of more than a very little water 
in either a liquid or a gaseous form. We may here say, that we do not 
agree with those authors who maintain that the curved or irregular form 
of the fluid-cavities is proof of the minerals having been in a soft state, 
since analogous facts are seen in the case of crystals deposited from solution. 
EXPLANATION OF PLATE. 
Figs. 1 & 2. Fluid-cavities in sapphire; magnified 20 linear. 
Fig. 3. Fluid-cavity in sapphire, partially divided by plates of sapphire ; 
mag. 50. 
Fig. 4. Branched fluid-cavity in sapphire ; mag. 50. 
Fig. 5. Crystal of spinel? inclosed in ruby; mag. 50. 
Fig. 6. Cavity in aquamarina, with two fluids ; mag. 150. 
Fig. 7. Cavity in ruby spinel ; mag. 100. 
Fig. 8. Fluicl-cavity in emerald, with soluble crystals ; mag. 200. 
Fig. 9. Crystal [inclosed in diamond, surrounded by a black cross, as 
seen with polarized light ; mag. 100, 
Fig. 10. Crystal inclosed in diamond, with a crack proceeding from it; 
mag. 100. 
Fig. 11. Crystal inclosed in ruby, surrounded by a black cross, seen by 
polarized light; mag. 75. 
Figs. 12 & 13, Crystals in ruby spinel, surrounded by various cracks, 
mag. 50. 
This paper was illustrated by means of the original specimens kindly 
lent by Mr Butler for the occasion, and displayed by means of tKe 
oxy-liydrogen lamp. 
