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A profusion of Calcedony, and fine specimens of Agate, were observed in many places, along the basaltic ridges. My black companions loaded themselves with the pretty agates, which they had never seen before, and which they evidently considered to be very valuable; but, after a little time, the weight became inconvenient, and they kept only a few, to strike fire with. Feb. 7.
In this neighbourhood considerable quantities both of zerlite and chabasite are also found, but, generally speaking, Iceland is less rich in minerals than one would suppose; opal, calcedony, amethyst, malachite, obsidian, agate, and feldspar, being the principal. Of sulphur the supply is inexhaustible.
M. de Carosi describes very systematically the generation of silex, calcedony, onyx, and quartz, in calcareous earth, marl, gypsum, sand-stone, and also what he terms terre glaise, ou de l'Argile. It is in this last that we find a perfect analogy with what is so frequent in this country of Scotland.
Were I however to conjecture upon a subject in which I have not any positive information, I should suppose that some part of the calcedony, like the oculus mundi when dipped in water, may be so transparent, while containing some portion of humidity, that it is not easily distinguishable from the gypsum in which it is concreted; but that in having the humidity evaporated, by being taken out of the mine and exposed to the dry air, those portions of calcedony, which did not before appear, may be perceived by becoming more opaque .
Those nodular bodies or figured parts which are here inclosed in the rock, are evidently what may be called calcedony agates.
The floor of the cavern was covered with heaps of water-worn fragments of quartzoze rock containing copper pyrites, in some of which the cavities were covered by a deposit of greenish calcedony.
These appearances are thought to be observed in the calcedony and ferruginous concretions, which has led some mineralists to conclude, that those concretions had been formed in the same manner, by means of water. We are now to show that these mineral appearances are not analogous to stalactites in their formation, and that they have evidently been formed in a different manner.
Both M. de Carosi, and also M. Macquart , to whom our author communicated his ideas and proper specimens, assert, that from their accurate experience, they find calcedony growing daily, not only in the solid body of gypsum, etc. while in the mine, but also in the solid stone when taktn out of the mine, and preserved in their cabinet.
It is now proposed to show that those conclusions are not well founded; and that, in this case of calcedony and iron-ore, it could not be upon the principle of stalactical concretion that the bodies now in question had their forms.
These are certain concretions of calcedony, and also of iron-ore, which are thought to have such resemblance to stalactical concretions as, by some superficial observers, to be reckoned of the same kind.
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