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As I have mentioned, the soundings from the great Atlantic plain are almost entirely made up of Globigerinoe, with the granules which have been mentioned, and some few other calcareous shells; but a small percentage of the chalky mud perhaps at most some five per cent. of it is of a different nature, and consists of shells and skeletons composed of silex, or pure flint.
In Western Banda Oriental, while the marine tertiary strata were accumulating, there were volcanic eruptions, much silex and lime were precipitated from solution, coarse conglomerates were formed, being derived probably from adjoining land, and layers of red mud and marly rocks, like those of the Pampean formation, were occasionally deposited.
Meanwhile an east wind arises, the fog disappears; when he thinks he has reached the suburbs of the city, Selkirk sees before him only an irregular assemblage of calcareous stones, crowned with dry herbs, or reddish, arid, angular rocks, flattened at their summits, tessellated with fragments of silex and mica, on which the sun is just pouring his rays; a company of goats, which the mist had condemned to a momentary repose, are bounding here and there, startling flocks of clamorous black-birds and plaintive sea-gulls; the fearless and yellow-crested woodpeckers alone do not stir, but continue to hammer with their sharp beaks at some old stunted trees.
Of the offices assigned to these creatures, the most familiar to common observation is the extraction of lime, and, more rarely, of silex, from the waters inhabited by them, and the deposit of these minerals in a solid form, either as the material of their habitations or as the exuviae of their bodies.
I measured one, which was fifteen feet in circumference: how surprising it is that every atom of the woody matter in this great cylinder should have been removed and replaced by silex so perfectly, that each vessel and pore is preserved! These trees flourished at about the period of our lower chalk; they all belonged to the fir- tribe.
The savage inhabitants of New Caledonia also, to appease their hunger in times of scarcity, eat great pieces of a friable Lapis ollaris. Vauquelin analysed this stone, and found in it, beside magnesia and silex in equal portions, a small quantity of oxide of copper.
It was, at first, supposed to be a meteor; but, when chemically examined, it proved to consist of silex, combined with potash, in the form in which it exists in grasses; and, upon further inquiry, it was ascertained that a stack of hay had stood upon the spot, of which nothing remained but the ashes, the whole having been ignited by the lightning.
The object of this treatise is to describe the generation of silex and quartz, with their modifications or compositions, formed within mineral bodies of a different substance. The natural history contained in this little treatise is well described and sufficiently interesting.
In like manner, by the resolution of the surrounding parts, the solid silex, which is supposed to be insoluble, is removed from its bed, and thus suffers new parts of the solid land to be exposed to those injuries of the air, by which the general good of plants, of animals, and even of future worlds, are consulted.
She did not forget her father, but it was impossible for her sweet and childlike nature to remain in mourning long. Professor Silex had felt a profound pity for his old friend's daughter, and had come down out of the clouds long enough to express it in scholarly terms and to offer any assistance in his power.
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