The vast extent of volcanic action, as indicated by extinct and active volcanos, would require a greater amount of these materials, than can be supposed to exist in the composition of the earth. Thus, according to the Newtonian test of a correct theory, the means, if true, would not be sufficient. Again: If sulphur and iron were the principal agents in producing volcanic action, and earthquakes, _volcanic products would give evidence of it_, by being, principally, _sulphate of iron_. So far is this from being the fact, that in 100 parts, volcanic product, Dr. Kennedy found, in reference to two volcanos, not exceeding 14.25 oxide of iron, and no sulphur at all. Volcanic products are generally, “mixtures of the earth in an oxidated and fused state, under intense ignition; water and saline substances, such as might be furnished by the sea and air, altered as might be expected from the formation of fixed oxidated matter.” URE. These two simple considerations must set aside the theory mentioned in the text. Other valid objections might be urged. As this theory is inadmissible, because, neither true in application to volcanic action and product, nor sufficient in force, it is proper to supply the deficiency. By a careful inspection of the phenomena attending volcanic action, as well as an examination of its products, we are clearly convinced, the _agents are aëriform_; chiefly _steam_ and the _gases_, and they act with an _expansive force from beneath_. Mouna Roa, in the island Owhyhee, rises 15,000 feet, and has on its top a crater _eight miles_ in circumference, containing a vast lake of molten lava. Mr. Goodrich visited it in 1824. He says, “exhalations escape from all the fissures of the lava crust, producing here and there a blast _like strong vapor blowing out of a steam boiler_.” Subsequently, a party from the Blonde frigate visited it, and the Rev. Charles Stewart, who accompanied the party, has given a description of the crater. He says, “its surface had all the agitation of the ocean. Billow after billow tossed its monstrous bosom into the air, and occasionally the waves from apposite directions met with such violence, as to dash the fiery spray, in the concussion, forty or fifty feet high.” _Ure’s New Syst. Geol._ pp. 381-2.