The COAL-MEASURES are also a remarkable item in the list of substances met with in beds and ranges, and claiming to be considered as rocks—for the coal is a petrifaction, perhaps a partial crystallization—but due to the deposition of vegetable matter, subjected afterwards to enormous hydrostatic pressure. We have no true estimate of their amount as yet, for fresh mines are being continually discovered; but here seems to consist the chief proportion of CARBON, as developed in this part of the visible creation.
CHALK constitutes one-eighth part of the crust of this globe. The mass of this must have been thrown up at once, when the atmosphere was eliminated, and the waters separated, and the sphere became condensed and solid. It is a “carbonate of lime” in its chemical description, and there is abundance of the limestone-rock all over the world; but it is very difficult to extract from this, in any quantity, the soft, friable, slightly unctuous mineral which goes by the name of chalk (Latin, “calx”).
The METALS exist in the rocks, generally some distance down in the earth’s interior. Their amount, in some instances, is very great indeed. The only one which is rarely met with on our globe, and then in small grains, is the NATIVE IRON, i.e. iron in its pure state. This want, however, could not have been recognized if we had not happened to find the substance in question in those blocks of meteoric iron, and in the small meteoric stones which have, from time to time, fallen to the surface of the earth during atmospheric storms, and, probably, owing to astronomical disturbances. For, of the iron, in its mixed conditions of different ores, we have an abundant supply. It is a singular fact, that the native gold, both in pure grains or flakes, and in solid “nuggets,” appears now to be the more prevalent form of that ponderous and imperishable substance. The ranges of quartz-rock in many chains of mountains are certainly thickly sown with seeds and nodules of fine gold.
I may mention here, as an interesting circumstance to mineralogists and collectors of fossil pebbles, that the “native iron,” which is so scarce on the surface of the ground, is met with, from time to time, along with manganese, in the heart of siliceous pebbles. But I have never seen it where there is not the presence of some animal organism.
Now all these solids, gold, iron, chalk, coal, salt—and I select incongruous items on purpose—are as truly portions of the earth’s mass as are the granite and slate, the sandstones and clays. And so are also the flowing waters and the suspended clouds; and so are also the component elements of these—oxygen, hydrogen, and the rest. It is, all of it, MATTER; it all obeys the law of gravitation, and it needs just as much to be taken into account, in a geological scheme or system, as the upheaving of granite rocks, the flux of lavas, or the icthyolite beds amidst the semi-crystalline ranges of the Old Red Sandstone formation.
Consequently I have found, as has partly I trust been shown in the preceding pages, that even to handle and pronounce upon a pebble, such an one as we can pick up on the sea-shore any summer’s day, all these elements must be taken into the account.
In a “moss-agate,” for instance, I discover—
First. A sandy cuticle, which we will rub off, as it is like the dust on your drawing-room table, a real thing, but out of place.
Secondly. Siliceous matter.
Thirdly. A purer form of this in chalcedony.