190 
PROCEEDINGS OF SOCIETIES. 
GrotocicaL Society, December 2d, 1857. 
On some peculiarities in the Microscopical Structure of 
Crystals, applicable to the determination of the Aqueous or 
Igneous Origin of Minerals and Rocks. By H. C. Sorsy, 
Ksq., F.R.S., F.G.S. 
In this paper the author showed that when artificial crys- 
tals are examined with the microscope, it is seen that they 
have often caught up and inclosed within their solid substance 
portions of the material surrounding them at the time when 
they were being formed. Thus, if they are produced by 
sublimation, small portions of air or vapour are caught up, so 
as to form apparently empty cavities ; or, if they are deposited 
from solution in water, small quantities of water are inclosed, 
so as to form fluid-cavities. In a similar manner, if crystals 
are formed from a state of igneous fusion, erystallizing out 
from a fused-stone solvent, portions of this fused stone be- 
come entangled, which, on cooling, remain in a glassy condi- 
tion, or become stony, so as to produce what may be called 
glass- or stone-cavities. All these kinds of cavities can readily 
be seen with suitable magnifying powers, and distinguished 
from each other by various definite peculiarities. 
From these and other facts, the following conclusions were 
deduced : 
1. Crystals containing only cavities with water were formed 
from solution. 
2. Crystals contaiming only stone- or glass-cavities were 
formed from a state of igneous fusion. 
3. Crystals containing both water- and stone- or glass- 
cavities were formed, under great pressure, by the combined 
influence of highly heated water and melted rock. 
4. That the relative amount of water present in the cavities 
may, in some cases, be employed to deduce the temperature 
at which the crystals were formed, since the accompanying 
vacuity is due to the contraction of the fluid on cooling. 
5. Crystals containing only empty cavities were formed by 
sublimation, unless the cavities are fluid-cavities that have 
lost their fluid, or are bubbles of gas given off from a sub- 
stance which was fused. 
