PYKOORY STALLING ROOKS. 
53 
ties at great depths in the sea. But the water when forced 
through the pores of a rock into cavities, becomes a powerful 
solvent of the earthy salts, which suffer also a transference of 
matter, which, on crystallizing, constitutes the regular crys¬ 
tals of geodes, cavities, or fissures. 
The result of the action of water proves to us that the 
alkalies and alkaline earths are present in the rock, and that 
water is competent to dissolve silica. 
The following exhibits 
the composition of 
Mesotype. 
Leucite, 
SileX, 
54*46 
53*75 
Alumina, 
19*70 
24*62 
Lime, 
1*61 
Soda, 
15*09 
Potash, 
21*35 
Water, 
9-83 
It is proper to remark that the foregoing minerals belong to 
the submarine division of the pyroplastic rocks. The condition 
of the submerged rocks is favorable to the development and 
formation of this natural family of minerals, while the sub¬ 
aerial divisions rarely contain minerals in their cavities, not 
indeed until they have been placed in favorable conditions for 
their production. In some instances the foregoing minerals 
appear to have been formed directly by heat. Those instances 
may be cited where a rock, as clay slate, has been altered 
by contact with a trap dyke. Both analcime and garnet 
have been formed in the slate by the heat of the trap. It is 
not however clear but that water in this, and most other cases 
of the kind, has been instrumental in the formation of the 
minerals under consideration. 
§ 43. Quartz and its group of associates . Quartz, when 
interlaminated with mica, forms mica slate, and when associ¬ 
ated in the same way with talc, forms the common talcose 
slates. These mixtures are variable. Sometimes one and 
sometimes the other predominates. But quartz, although it 
occurs in the relations I have stated, still it does not seem to 
hold that relation to talc or mica that feldspar holds to augite 
