out ete recouvertes par ses eaux.  La zeolite des laves n’est point une dejection volcanique, ni une production du feu, ni meme un matiere que les laves aient enveloppee lorsqu’elles etoient fluides; elle est le resultat d’une operation et d’une combinaison posterieure, auxquelles les eaux de la mer ont concouru.  Les laves qui n’ont pas ete submergees, n’en contiennent jamais.  J’ai trouve ces observations si constantes, que par-tout ou je rencontrois de la zeolite, j’etois sur de trouver d’autres preuves de submersion, et partout ou je voyois des laves recouvertes des depots de l’eau, j’etois sur de trouver de la zeolite, et un de ces faits m’a toujours indique l’autre.  Je me suis servi avec succes de cette observation pour diriger mes recherches, et pour connoitre l’antiquite des laves. Mineralogie de Volcans, par M. Faujas de Saint-Fond.  Here would appear to be the distinction of subterraneous lava, in which zeolite and calcareous spar may be found, and that which has flowed from a volcano, in which neither of these are ever observed.]

There can be no doubt that these two different species of bodies have had the same origin, and that they are composed of the same materials nearly; but from the different circumstances Of their production, there is formed a character to these bodies, by which, they may be perfectly distinguished.  The difference of those circumstances consists in this; the one has been emitted to the atmosphere in its fluid state the other only came to be exposed to the light in a long course of time, after it had congealed under the compression of an immense load of earth, and after certain operations, proper to the mineral regions, had been exercised upon the indurated mass.  This is the cause of the difference between those erupted lavas, and our whin-stone, toad-stone, and the Swedish trap, which may be termed subterraneous lava.  The visible effects of those different operations may now be mentioned.

In the erupted lavas, those substances which are subject to calcine and vitrify in our fires, suffer similar changes, when delivered from a compression which had rendered them fixed, though in an extremely heated state.  Thus, a lava in which there is much calcareous spar, when it comes to be exposed to the atmosphere, or delivered from the compressing force of its confinement, effervesces by the explosion of its fixed air; the calcareous earth, at the same time, vitrifies with the other substances.  Hence such violent ebullition in volcanos, and hence the emission of so much pumice-stone and ashes, which are of the same nature.

In the body of our whin-stone, on the contrary, there is no mark of calcination or vitrification.  We frequently find in it much calcareous spar, or the terra calcarea aerata, which had been in a melted state by heat, and had been crystallized by congelation into a sparry form.  Such is the lapis amygdaloides, and many of our whin-stone rocks, which contain pebbles crystallized and variously figured, both calcareous, siliceous, and of a mixture in which both these substances form distinct parts.  The specimens of this kind, which I have from the whin-stone or porphyry rock of the Calton-hill, exhibit every species of mineral operation, in forming jasper, figured agate, and marble; and they demonstrate, that this had been performed by heat or fusion.