B. Water-silices. Water-clays. Water-talcs. Water-calces. 8. Hornstone. 8. Clay-slate. 8. Serpentine. 8. Hydrophyllite.
C. Air-silices. Air-clays. Air-talcs. Air-calces. 9. Tripoli. 9. Clay-stone. 9. Lithomarge. 9. Gypsum.
D. Fire-silices. Fire-clays. Fire-talcs. Fire-calces. 10. Obsidian. 10. Lava. 10. Basalt. 10. Limestone.
571. Now we here observe that only Quartz, Hornstone, Tripoli and Obsidian, occur as mineral aggregates in large masses, while all the others are only rare precious stones. Among the Clays, only Felspar, Clay-Slate, Hornstone and Lava. Among the Talcs, only Mica, Serpentine, Lithomarge, and Basalt. Among the Calcareous-earths, which incline towards the nature of salts, all the first families are of rare occurrence, and the latter only appear as mineral masses. This regularity speaks moreover retrospectively in favour of the correctness of the classification. The families have thus the same import or value in Geology as in Oryctognosy.
572. The proper organs of the planet are the mineral aggregates or rocks. These are either presented to us as they have originally been precipitated from water by chemical process, or as they have been changed by the co-operation of the other elements. There are thus _genetic_ and _metamorphosed_ kinds of rock. The former were crystallized previous to the current of the water--_Primary rocks_. These rocks are changed either--
1. By water--Transition-rocks, or 2. By air--Trappean-rocks. 3. By fire--Volcanic-rocks.
There are properly four kinds of rock formations--
1. Earth-formation, masses that have originated through the crystallizing force of the earth-element itself--Primary-rocks. 2. Aqueous-formation--Transition-rocks. 3. Aerial-formation--Trappean-rocks. 4. Igneous-formation--Volcanic-rocks.
The stratified rocks, having originated for the most part mechanically, are only the object of Physio-philosophy, in so far as chemical precipitations partly occur amongst them.
573. The earth-formation is represented by the crystallized primary rocks.
574. The earths can only be precipitations from the element that immediately precedes them, and thus from water. They have been enveloped in the water, as this has been in the air, and the latter again in the æther, but not mechanically, as we at present dissolve clay in water, nor chemically either, as lime dissolves by corrosion in water, but dynamically. The water did not exist from the beginning as water in the air, but only its principles, which became for the first time water, when they had combined by electricity.