52 
AMERICAN GEOLOGY. 
spars. The following tables exhibit the composition of the 
most important: 
Analeirae. 
Laumonite, 
Silex, 
58-00 
48-30 
Alumina, 
18-00 
22-70 
Soda, 
1000 
Lime, 
2-00 
12-10 
Water, 
8-50 
16-00 
Laumonite is remarkable for its instability, which is due to 
loss of its water, when it becomes a white powder. It efflor- 
vesces in the dry atmosphere. 
Stilbite. 
Heulandite. 
Silex, 
58-08 
59'00 
Alumina, 
16-10 
7-19 
Lime, 
9-20 
16-87 
Water, 
16-40 
13-45 
Oxide of iron, 
io-oo 
The foregoing family of minerals seem to be due to the sol° 
vent action of water. The elements existing in the parent 
rock are dissolved out under favorable circumstances. The 
igneous rocks are more or less porous, and hence admit of its 
transfusion through the mass. If a cavity be opened in a 
rock, however deep its situation, it is almost impossible to 
exclude the entrance of water into it, provided the rock is not 
absolutely anhydrous. At the surface the pressure by which 
water would be forced into a cavity (which may be regarded 
as a vacuum) equals fifteen pounds to the square inch: under 
water the pressure would be greatly increased. The solvent 
power of water is aided by pressure; hence the transfusion of 
water into cavities may be accounted for, and indeed provided 
for, and in its progress through the rock must necessarily dis¬ 
solve and carry forward the soluble matter with which it meets. 
The idea of the transfusion of water into cavities and pores 
in rocks beneath the sea, is illustrated by Dr. Scoreby’s account 
of a boat pulled down to a considerable depth by a whale, after 
which the wood became too heavy to float, the air being forced 
out and replaced by wafer. So also the filling of empty bot- 
