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Updated: June 6, 2025
A gritty silicious rock on the banks of the Euphrates, a little above Hit, was suitable for mill-stones. The gems furnished by the various provinces of the Empire are too numerous for mention. They included, it must be remembered, all the kinds which have already been enumerated among the mineral products of the earlier Monarchies.
But there is another chalk known as Barbados earth; it is silicious, and is ultimately composed of minute and beautiful skeletons such as those which, enormously magnified, you now see. These were the glassy envelopes which protected the living speck that dwelt within and built it.
The evidence respecting the corresponding Arctic area is less complete, but it is sufficient to justify the conclusion that an essentially similar silicious cap is being formed around the northern pole.
Desmidiaceae. Microscopic gelatinous plants, of a screen color, growing in fresh water, composed of cells devoid of a silicious coat, of peculiar forms such as oval, crescentic, shortly cylindrical, cylindrical, oblong, etc., with variously formed rays or lobes, giving a more or less stellate form, presenting a bilateral symmetry, the junction of the halves being marked by a division of the green contents; the individual cells being free, or arranged in linear series, collected into fagot-like bundles or in elegant star like groups which are embedded in a common gelatinous coat.
An attentive study of the conditions favorable to the propagation of the diatomaceae might perhaps help us to profit directly by the productivity of this organism, and, at the same time, disclose secrets of nature capable of being turned to valuable account in dealing with silicious rocks, and the metal which is the base of them.
How does such a delicate ornament answer the demands of mere conspicuousness? But there is a stronger case than this. I before alluded to the exquisite symmetry of the silicious and crystalline coverings of some of the simplest forms of marine animalcules; and also I may here add the beautiful colouring of shells sometimes on the inside.
The cones are about four inches long, exceedingly hard, and covered with a sort of silicious varnish and gum, rendering them impervious to moisture, evidently with a view to the careful preservation of the seeds. No other conifer in the range is so closely restricted to special localities.
But the use of a spatula and a small piece of polished stone slab will show that the entire discharge is excrementitious matter, with the single exception of this silicious coating of the seeds. The case is different, however, with the fruit-eating birds.
The underclays are found beneath every bed of coal. "Warrant," "spavin," and "gannister" are local names which are sometimes applied to it, the last being a term used when the clay contains such a large proportion of silicious matter as to become almost like a hard flinty rock.
These kames and sand plains, because of the silicious nature of their materials and the very porous nature of the soil which they afford, are commonly sterile, or at most render a profit to the tiller by dint of exceeding care.
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