52. Native copper is very abundant; and some specimens of it have been found crystallized. Here the crystallization of the metal is a proof that it has passed from a fluid to a solid state; and its purity is a proof that it did not make that transition by being precipitated from a menstruum. 53. Again, pieces of native manganese have been found possessing so exactly the characters peculiar to that metal when reduced in our furnaces, that it is impossible to consider them as deriving their figure and solidity from any cause but fusion. The ingenious author who describes these specimens, La Peyrouse, was so forcibly struck with this resemblance, that he immediately drew the same conclusion from it which is drawn here, attributing the only difference, which he remarked between the native and the artificial _regulus_, to the different energy with which the same agent works when employed by nature and by art.[17] [Footnote 17: Theory of the Earth, vol. i. p. 68. Journal de Phys. Janvier, 1786.] 54. All these appearances conspire to prove, that the materials which fill the mineral veins were melted by heat, and forcibly injected, in that state, into the clefts and fissures of the strata. These fissures we must conceive to have arisen, not merely from the shrinking of the strata while they acquired hardness and solidity, but from the violence done to them, when they were heaved up and elevated in the manner which has already been explained.[18] [Footnote 18: NOTE XIII.] 55. When these suppositions are once admitted, the other leading facts in the history of metallic veins will be readily accounted for. Thus, for instance, it is evident to what we must ascribe the fragments of the surrounding rock that are often found immersed in the veins, and encompassed on all sides by crystallized substances. These fragments being no doubt detached by the concussion, which at once tore asunder and elevated the strata, were sustained by the melted matter that flowed at the same time upward through the vein. Large masses of rock are often found in this manner completely insulated; one of these, which M. De Luc has described with great accuracy, is no less than a vast segment of a mountain.[19] [Footnote 19: Lettres Physiques, &c. tom. iii. P. 361.]