it may commit, an attempt has been made to insinuate its uncertainty and even its inutility. But what science is there which would not be annihilated the moment that we made its truth and its usefulness to depend on the exact degree of correspondence that might subsist between the opinions of those philosophers who make it the subject of their study? If there exist some difference in the opinions entertained by the Abbé Haüy and myself on certain points in crystallography, what conclusion ought to be deduced from this circumstance? simply that this science, which on the one hand is supported by physics, and on the other by mathematics, and will perhaps at some future day become equally exact with the latter, has not yet obtained that certainty. Let us allow it to proceed towards this point, without obstructing its course. Difference of opinion when maintained with candour and decorum is perhaps not without advantage to the security and promptitude of its progress.
General observations on the Laumonite.
The laumonite has never hitherto been discovered except in a crystallized state, either in separate crystals, which is the most common appearance, or in an aggregation of crystals, forming masses of more or less considerable size for the most part irregular, and deeply striated externally.
Till the present time the laumonite had been observed only in the lead mine of Huelgoet in lower Brittany, in which it was discovered about twenty-five years ago by M. Gillet de Laumont.[1]
- ↑ It lines the walls of the vein, conjointly with a lamellar carbonate of lime belonging to that variety in which the rhomboidal fragments are striated in the direction of the greater diagonal of two of the opposite faces. This carbonate of lime, which is perfectly colourless, is one of the most phosphorescent which I have ever seen. It I may judge of the rock from the portions of it remaining attached to the pieces which I have examined, the walls of the vein, to which this substance, with the carbonate of lime which accompanies it, adheres, consist of a ferruginous argillaceous schist of a deep blackish-grey colour, of a very loose texture, and traversed by small veins of carbonate of lime. A moderate action of the tire changes this colour to a reddish-brown, and at the same time renders this schist extremely attractable by the magnet; its texture likewise becomes more loose, and when examined with a glass and by the light of the sun, this substance appears to be formed of a mass of small and extremely thin scales: its aspect is then much like that which would be presented by a mass of chlorite of the same colour, and of a fine grain. I am indebted to M. Gillet de Laumont for another very fine specimen of this mineral which I have received since that mentioned in the first part of this paper, in which the crystals of laumonite are very large and regular and beautifully grouped with crystals of carbonate of lime. The base of this specimen bears very evident marks of its having been detached from the schist which I have just described.
