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 dykes. Similar dykes 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 the mineral characters of these dykes present insensible gradations, from a state of compact lava, through infinite varieties of greenstone, serpentine, and porphyry to granite, we refer them all to a common igneous origin.

The sources from which the matter of these ejected rocks ascends are deeply seated beneath the granite; but it is not yet decided whether the immediate cause of an eruption be the access of water to local accumulations of the metalloid bases of the earths and alkalies; or whether lava be derived directly from that general mass of incandescent elements, which may probably exist at a depth of about one hundred miles beneath the surface of our planet.*

See chapter on the internal temperature of the earth.

Our section shows how closely the results of volcanic forces now in action are connected, both with the phenomena of basaltic formations, and also with the more ancient eruptions of greenstone, porphyry, syenite, and granite. The intrusion both of dykes and irregular beds of unstratified crystalline matter, into rocks, of every age and every formation, all proceeding upwards from an unknown depth, and often accumulated into vast masses overlying the surface of stratified rocks, are phenomena coextensive with the globe.

Throughout all these operations, however turbulent and apparently irregular, we see ultimate proofs of method and design, evinced by the uniformity of the laws of matter and motion, which have ever regulated the chemical and mechanical forces by which such grand effects have been produced. If we view their aggregate results, in causing the elevation of land from beneath the sea, we shall find that volcanic forces assume a place of the highest importance, among the second causes which have influenced the past, as well as the present condition of the globe; each individual movement has contributed its share towards the final object, of conducting the molten materials of an uninhabitable planet, through long successions of change and of convulsive movements, to a tranquil state

of equilibrium; in which it has become the convenient and delightful habitation of man, and of the multitudes of terrestrial creatures that are his fellow tenants of its actual surface.*

CHAPTER VI.

Primary Stratified Rocks.

In the summary we have given of the leading phenomena of unstratified and volcanic rocks, we have unavoidably been led into theoretical speculations, and have seen that the most probable explanation of these phenomena is found in the hypothesis of the original fluidity of the entire materials of the earth, caused by the presence of intense heat. From this fluid mass of metals, and metalloid bases of the earths, and alkalies, the first granitic crust appears to have been formed, by oxydation of these bases; and subsequently broken into fragments, disposed at unequal levels above and below the surface of the first formed seas.

Wherever solid matter arose above the water, it became exposed to destruction by atmospheric

* See further details respecting the effects of volcanic forces in the description of Pl. I. Vol. ii.

agents; by rains, torrents, and inundations; at that time probably acting with intense violence, and washing down and spreading forth, in the form of mud and sand and gravel, upon the bottom of the then existing seas, the materials of primary stratified rocks, which, by subsequent exposure to various degrees of subterranean heat, became converted into beds of gneiss, and mica slate, and hornblende slate, and clay slate. In the detritus thus swept from the earliest lands into the most ancient seas, we view the commencement of that enormous series of derivative strata which, by long continued repetition of similar processes, have been accumulated to a thickness of many miles.*

The total absence of organic remains through

* Mr. Conybeare (in his admirable Report on Geology to the British Association for the Advancement of Science, 1832, p. 367) shows, that many of the most important principles of the igneous theory, which has been almost demonstrated by modern discoveries, had been anticipated by the universal Leibnitz. "In the fourth section of his Protogæa, Leibnitz presents us with a masterly sketch of his general views, and, perhaps, even in the present day, it would be difficult to lay down more clearly the fundamental positions which must be necessarily common to every theory, attributing geological phenomena in great measure to central igneous agency. He attributes the primary and fundamental rocks to the refrigeration of the crust of this volcanic nucleus; an assumption which well accords with the now almost universally admitted igneous origin of the fundamental granite, and with the structure of the primitive slates, for the insensible gradation of these formations appears to prove that gneiss must have undergone in a greater,