That is very curious! and I suppose that petrified animal substances are of the same nature?
MRS. B.
Precisely. It is equally impossible for either animal or vegetable substances to be converted into stone. They may be reduced, as we find they are, by decomposition, to their constituent elements, but cannot be changed to elements, which do not enter into their composition.
There are, however, circumstances which frequently prevent the regular and final decomposition of vegetables; as, for instance, when they are buried either in the sea, or in the earth, where they cannot undergo the putrid fermentation for want of air. In these cases they are subject to a peculiar change, by which they are converted into a new class of compounds, called bitumens.
CAROLINE.
These are substances I never heard of before.
MRS. B.
You will find, however, that some of them are very familiar to you. Bitumens are vegetables so far decomposed as to retain no organic appearance; but their origin is easily detected by their oily nature, their combustibility, the products of their analysis, and the impressions of the forms of leaves, grains, fibres of wood, and even of animals, which they frequently bear.
They are sometimes of an oily liquid consistence, as the substance called naptha, in which we preserved potassium; it is a fine transparent colourless fluid, that issues out of clays in some parts of Persia. But more frequently bitumens are solid, as asphaltum, a smooth, hard, brittle substance, which easily melts, and forms, in its liquid state, a beautiful dark brown colour for oil painting. Jet, which is of a still harder texture, is a peculiar bitumen, susceptible of so fine a polish, that it is used for many ornamental purposes.
Coal is also a bituminous substance, to the composition of which both the mineral and animal kingdoms seem to concur. This most useful mineral appears to consist chiefly of vegetable matter, mixed with the remains of marine animals and marine salts, and occasionally containing a quantity of sulphuret of iron, commonly called pyrites.