Extract

Silica is a substance so general in its presence and so universal in its action in the crust of the earth, that it may be worth our while to examine somewhat minutely into the details of its nature from a chemical point of view. There are one or two points of interest connected with this subject which have not yet had the attention from our Society which they seem to deserve.

To begin at the root of our subject, then, silica or silicic acid is a compound of the two elementary substances silicon and oxygen, and is represented by the symbols Si.O₃. Of all the components of the earth’s crust, there is perhaps no substance so universally and so abundantly present as silica, whether in the free state as in the form of sand, quartz, flint, and so forth; or in combination, as clays, shales, and nearly all the hard rocks. There is almost no rock in which we do not find it more or less abundantly, and almost no condition of the earth’s crust in which its action is not palpable. It may be represented as the bone or skeleton of the earth, ever tending to bind and render the other constituents hard and compact. Throughout the countless ages of the various stages of geological history, it has acted in a great measure as the preserver of fossils, those records so essential to the study of geology. It is a principal constituent of granites, porphyries, clays, slates, &c., and

This 250-word extract was created in the absence of an abstract