The variety of these sulphureo-metallic substances, in point of composition, is almost indefinite; but, unless they were all soluble in water, this could not have happened by the action of that solvent.  If we shall allow any one of those bodies to have been formed by the fluidity of heat, they must all have been formed in the same manner; for there is such a chain of connection among those bodies in the mineral regions, that they must all have been composed, either, on the one hand, by aqueous solution, or, on the other, by means of heat and fusion.

Here, for example, are crystallised together in one mass, 1_st, Pyrites_, containing sulphur, iron, copper; 2_dly, Blend_, a composition of iron, sulphur, and calamine; 3_dly, Galena_, consisting of lead and sulphur; 4_thly, Marmor metallicum_, being the terra ponderosa, saturated with the vitriolic acid; a substance insoluble in water; 5_thly, Fluor_, a saturation of calcareous earth, with a peculiar acid, called the acid of spar, also insoluble in water; 6_thly, Calcareous spar_, of different kinds, being calcareous earth saturated with fixed air, and something besides, which forms a variety in this substance; lastly, Siliceous substance, or Quartz crystals.  All these bodies, each possessing its proper shape, are mixed in such a manner as it would be endless to describe, but which may be expressed in general by saying, that they are mutually contained in, and contain each other.

Unless, therefore; every one of these different substances may be dissolved in water, and crystallised from it, it is in vain to look for the explanation of these appearances in the operations of nature, by the means of aqueous solution.

On the other hand, heat being capable of rendering all these substances fluid, they may be, with the greatest simplicity, transported from one place to another; and they may be made to concrete altogether at the same time, and distinctly separate in any place.  Hence, for the explanation of those natural appearances, which are so general, no further conditions are required, than the supposition of a sufficient intensity of subterraneous fire or heat, and a sufficient degree of compression upon those bodies, which are to be subjected to that violent heat, without calcination or change.  But, so far as this supposition is not gratuitous, the appearances of nature will be thus explained.

I shall only mention one specimen, which must appear most decisive of the question.  It is, I believe, from an Hungarian mine.  In this specimen, petro-silex, pyrites, and cinnabar, are so mixed together, and crystallised upon each other, that it is impossible to conceive any one of those bodies to have had its fluidity and concretion from a cause which had not affected the other two.  Now, let those who would deny the fusion of this siliceous body explain how water could dissolve these three different bodies, and deposit them in their present shape.  If, on the contrary, they have not the least shadow of reason for such a gratuitous supposition, the present argument must be admitted in its full force.