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Updated: June 1, 2025
Here is described very distinctly an appearance which is very common or general on those occasions; this is the parts or particles of stone floating in the fluid siliceous substance, and there dissolving more or less.
This stone presented yellowish concentric lines and bands, on a reddish brown ground. It appeared to me that the round pieces of Egyptian jasper belonged also to the Barcelona limestone. Yet, according to M. Cordier, the fine pebbles of Suez owe their origin to a breccia formation, or siliceous agglomerate.
This water, therefore, not only contains siliceous substance in a dissolved state, but deposits this again, either by means of cooling, or being aerated, or of evaporating. Consequently, without knowing the principle upon which it proceeds, we here perceive a natural operation by which siliceous petrifaction may be performed.
It is not, however, a true breccia, but a pudding-stone, composed, not of calcareous but of siliceous fragments; and these fragments are not angular, as in the true breccias, but rounded, indicating that they had been carried by water and consequently rounded by attrition. The connected pebbles must have been broken from rocks of great hardness to have withstood the effects of constant abrasion.
It is remarkable that the chalk WITH flint abounds in the north of Europe; that WITHOUT flints in the south; while in the northern chalk siliceous animalcules are wanting, and in the southern present in great quantities.
Immediately upon the chalk at the bottom of all the tertiary strata in France there generally is a conglomerate or breccia of rolled and angular chalk-flints, cemented by siliceous sand. These beds appear to be of littoral origin, and imply the previous emergence of the chalk, and its waste by denudation.
These two species of bodies, therefore, the siliceous and the sulphureous, may now be examined, in relation to the causes of their concretion, with a view to determine, what has been the general concreting or consolidating power, which has operated universally in the globe; and particularly to show, it has not been by means of any fluid solution, that strata in general have been consolidated, or that those particular substances have been crystallized and concreted.
The shells out of the layers of brown limestone, included in the black calcareous shale-rock, which latter, as just stated, replaces the white siliceous sandstone, consist of: Pecten Dufreynoyi, d'Orbigny, "Voyage" Part Pal. Turritella Andii, d'Orbigny, "Voyage" Part Pal. Astarte Darwinii, E. Forbes. Gryphaea Darwinii, E. Forbes. An intermediate form between G. gigantea and G. incurva.
See ante, iii. 293, for Johnson's rebuke of Hannah More's flattery. Johnson, in his Dictionary, defines calamine or lapis calaminaris as a kind of fossile bituminous earth, which being mixed with copper changes it into brass. It is native siliceous oxide of zinc. The Imperial Dictionary. See ante, iii. 164. 'No' or 'little' is here probably omitted.
I brought away specimens of one of the tufaceous layers of a pinkish colour and it is a most extraordinary fact, that Professor Ehrenberg finds it almost wholly composed of matter which has been organized: he detects in it some siliceous-shielded fresh-water infusoria, and no less than twenty-five different kinds of the siliceous tissue of plants, chiefly of grasses.
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