The base of _silica_ is SILICIUM. There exists some doubts among chemists whether this base is indeed a _metal_; but there is no doubt but that it is _combustible_, and that the earth silica, (or silex,) is an _oxide_. From _analogy_ it would be inferred this base is metallic, and the _evidence_ preponderates on this side. This oxide, or earth, is very abundant. It is more commonly called _silex_. It is the base of the whole class of primitive rocks, and almost altogether constitutes quartz, flint, &c. The reader is now desired to recollect that this class of metals constitutes the _bases of the alkalis, and earths_; which are simply _metallic oxides_ or a combination of oxygen with the metals. Recollect also that _all these metals are inflammable_, and some of them simply upon exposure to air and water. Now as the earths at the surface of our globe are the results of _chemical action_, in which the oxygen combined with the metals, it is beyond a doubt that these substances were created in their elementary and uncombined state; and that the act of combining would produce an inconceivable amount of heat, so as to fuse completely the whole mass of our earth; and in this state of fusion the oxides would commence forming at the _surface chiefly_; and thus by oxidizing the metals would form the earths, rocks, &c, which constitute, principally, the _crust_ of our globe. When this crust became sufficiently thick it would protect the _interior_ parts of the earth from oxidation, by preventing the access of air and water; and they would of course remain in a pure metallic state. But, (as is most probable,) if the materials, being promiscuously mixed throughout the mass at the commencement of the chemical action, should oxidize throughout, then the indurating of the crust, by cooling, would inclose the _interior_ parts _in a state of fusion_, and in that state they remain to the present time. Nor is this astonishing when we recollect the _earths_ are almost perfect _non-conductors of caloric_: of course it could not escape at all through the _crust_ of the earth, formed of many strata of earths, in the shape of rocks, which, taken together, may be about eight miles thick. If, by any concussion, or by percolation, water, or air should reach these metals in the interior, or these fused masses of matter, the consequence would be _decomposition_, and the production of a great amount of gas, and heat, which operating conjointly, first produce earthquakes by struggling to escape from the caverns in which they are generated; and when they find a passage, they would break forth into volcanos. This is the only true and satisfactory theory of earthquakes and volcanos.