Mineralogists Who Think That The End Of The Geology Of Volcanoes Is The Classification Of Lavas, The Examination Of The Crystals They Contain, And Their Description According To Their External Characters, Are Generally Very Well Satisfied When They Come Back From The Mouth Of A Burning Volcano.

They return loaded with those numerous collections, which are the principal objects of their research.

This is not the feeling of those who, without confounding descriptive mineralogy (oryctognosy) with geognosy, endeavour to raise themselves to ideas generally interesting, and seek, in the study of nature, for answers to the following questions: -

Is the conical mountain of a volcano entirely formed of liquified matter heaped together by successive eruptions, or does it contain in its centre a nucleus of primitive rocks covered with lava, which are these same rocks altered by fire? What are the affinities which unite the productions of modern volcanoes with the basalts, the phonolites, and those porphyries with bases of feldspar, which are without quartz, and which cover the Cordilleras of Peru and Mexico, as well as the small groups of the Monts Dores, of Cantal, and of Mezen in France? Has the central nucleus of volcanoes been heated in its primitive position, and raised up, in a softened state, by the force of the elastic vapours, before these fluids communicated, by means of a crater, with the external air? What is the substance, which, for thousands of years, keeps up this combustion, sometimes so slow, and at other times so active?

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