679. The inundations of water were in general necessary, because basins of land and precipitations were everywhere present; but not all on that account at the same time.
680. In this sense there was a general flood, a deluge, namely, for every land.
c. Air-formation.
TRAP-ROCKS.
681. Vapours and gases of different kinds may be contained in the interior of the earth in two ways, either chemically combined as carbonic acid, or mechanically inclosed in cavities of the earth. Both may be developed, or expanded by calefaction, and the latter by diminution of pressure.
682. If those that are chemically combined be developed by calefaction, they then form vesicular spaces in the masses of earth whereby the latter are extended and raised above the surface; such as amygdaloid, basalt and others of this kind.
683. Warm springs may originate by subterraneous processes, chemical or volcanic; probably, too, by the compression of air that has forced its way into these situations.
684. Earthquakes may indeed originate in different ways; as in addition to the falling in of cavities, by the chemical development also of gases, by their subjection to heat, by aqueous vapours, and also by the sudden diminution of pressure upon these incarcerated gases.
685. This diminution of pressure proceeds from sudden rarefaction of the atmosphere—due probably to the disappearance of air in a particular place, or resulting from a change of the wind, or the formation of heavy rain. Earthquakes can therefore extend through many countries, without requiring to depend upon each other or on a common focus of action.
686. The silicious trap is silicious sinter, tripoli and polierschiefer.