Elements of geology / by Charles Lyell.

  • Charles Lyell
Date:
1838
Catalogue details

Licence: Public Domain Mark

Credit: Elements of geology / by Charles Lyell. Source: Wellcome Collection.

    56/582 page 26
    respectively of sand, clay, and carbonate of lime. Of these, the arenaceous, or sandy masses, are chiefly made up of siliceous or flinty grains; the argillaceous, or clayey, of a mixture of siliceous matter, with a certain proportion, about a fourth in weight, of aluminous earth ; and, lastly, the calcareous rocks or limestones consist of carbonic acid and lime. Arenaceous or siliceous rocks. —‘To speak first of the sandy division: beds of loose sand are fre- quently met with, of which the grains consist en- tirely of silex, which term comprehends all purely siliceous minerals, as quartz and common flint. Quartz is silex in its purest form; flint usually contains some admixture of alumine and oxide of iron. The siliceous grains in sand and sandstone are usually rounded, as if by the action of running water; but they sometimes, though more rarely, consist of small crystals, as if they had been che- mically precipitated from a fluid containing silex in solution. Sandstone is an aggregate of such grains, which often cohere together without any visible cement, but more commonly are bound together by a slight quantity of siliceous or calcareous matter, or by iron or clay. In nature there is every intermediate gradation, from perfectly loose sand, to the hard- est sandstone. In micaceous sandstones mica is abundant; and the thin silvery plates into which
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