Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/50

 46 stability. Very different are the feelings of those whose lot is cast near the foci of volcanic eruptions; to them the earth affords no stable resting place, but during the paroxysms of volcanic activity, reels to and fro, and vibrates beneath their feet; overthrowing cities, yawning with dreadful chasms, converting seas into dry lands, and dry lands into seas. (See Lyell's Geology, vol. i. passim.)

To the inhabitants of such districts we speak a language which they fully comprehend, when we describe the crust of the globe as floating on an internal nucleus of molten elements; they have seen these molten elements burst forth in liquid streams of lava; they have felt the earth beneath them quivering and rolling, as if upon the billows of a subterranean sea; they have seen mountains raised and valleys depressed, almost in an instant of time; they can duly appreciate, from sensible experience, the force of the terms in which geologists describe the tremulous throes, and convulsive agitations of the earth; during the passage of its strata from the bottom of the seas, in which they received their origin, to the plains and mountains in which they find their present place of rest.

We see that the streams of earthy matter, which issue in a state of fusion from active volcanos, are spread around their craters in sheets of many kinds of lava; some of these so much resemble beds of basalt, and various trap rocks, that occur in districts remote from any existing volcanic vent, as to render it probable that the latter also have been poured forth from the interior of the earth. We further find the rocks adjacent to volcanic craters, intersected by rents and fissures, which have been filled with injections of more recent lava, forming transverse walls or dikes. Similar dikes occur not only in districts occupied by basalt and trap rocks, at a distance from the site of any modern volcanic activity; but also in strata of every formation, from the most ancient primary, to the most recent tertiary (see Plate 1. section f 1—f 8. h 1—h 2. i 1—i 5): and as