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sand and gravel, would for ever have remained beneath the surface of the water, had not other forces been subsequently employed to raise them into dry land: these forces appear to have been the same expansive powers of heat and vapour which, having caused the elevation of the first raised portions of the fundamental crystalline rocks, continued their energies through all succeeding geological epochs, and still exert them in producing the phenomena of active volcanos; phenomena incomparably the most violent that now appear upon the surface of our planet.*

The evidence of design in the employment of forces, which have thus effected a grand general purpose, viz. that of forming dry land, by elevating strata from beneath the waters in which they were deposited, stands independent of the truth or error of contending theories, respecting the origin of that most ancient class of stratified rocks, which are destitute of organic remains (see pi. 1.—section 1,2,3, 4, 5, 6, 7.) It is immaterial to the present question, whether they were formed (according to the theory of Hutton) from the detritus of the earlier granitic rocks, spread forth by water into beds of clay and sand; and subsequently modi

• "The fact of great and frequent alteration in the relative level of the sea and land is so well established, that the only remaining questions regard the mode in which these alterations have been effected, whether by elevation of the land itself, or subsidence in the level of the sea? And the nature of the force which has produced them? The evidence in proof of great and frequent movements of the land itself, both by protrusion and subsidence, and of the connexion of these movements with the operations of volcanos, is so various and so strong, derived from so many different quarters on the surface of the globe, and every day so much extended by recent inquiry, as almost to demonstrate that these have been the causes by which those great revolutions were effected; and that although the action of the inward forces which protrude the land has varied greatly in different countries, and at different periods, they are now and ever have been incessantly at work in operating present change and preparing the way for future alteration in the exterior of the globe."— Geological sketch of the Vicinity of Hastings, by Dr. Fitton, pp. 85, 86.

44 RELATION OF UNSTRATIFIED TO STRATIFIED ROCKS.

fied by heat: or whether they have been produced, (as was maintained by Werner) by chemical precipitation from a fluid, having other powers of solution than those possessed by the waters of the present ocean. -It is of little importance to our present purpose, whether the non-appearance of animals and vegetables in these most ancient strata was caused by the high temperature of the waters of the ocean, in which they are mechanically deposited; or by the compound nature and uninhabitable condition of a primeval fluid, holding their materials in solution. All observers admit that the strata were formed beneath the water, and have been subsequently converted into dry land: and whatever may have been the agents that caused the movements of the gross unorganized materials of the globe; we find sufficient evidence of prospective wisdom and design, in the benefits resulting from these obscure and distant revolutions, to future races of terrestrial creatures, and more especially to Man.*

* In describing geological phenomena, it is impossible to avoid the use of theoretical terms, and the provisional adoption of many theoretical opinions as to the manner in which these phenomena have been produced. From among the various and conflicting theories that have been proposed to explain the most difficult and complicated problems of Geology, I select those which appear to carry with them the highest degree of probability; but as results remain the same from whatever cause they have originated, the force of inferences from these results will be unaffected by changes that may arise in our opinions as to the physical causes by which these have been produced. As in estimating the merits of the highest productions of human art it is not requisite to understand perfectly the nature of the machinery by which the work has been effected in order to appreciate the skill and talent of the artist by whom it was contrived; so our minds may be fully impressed with a perception of the magnificent results of creative intelligence, which are visible in the phenomena of nature, although we can but partially comprehend the mechanism that has been instrumental to their production; and although the full development of the workings of the material instruments by which they were effected, has not yet been, and perhaps may never be, vouchsafed to the prying curiosity of man.

In unstratified crystalline rocks, wholly destitute of animal or vegetable remains, we search in vain for those most obvious evidences of contrivance, which commence with the first traces of organic life, in strata of the transition period; the chief agencies which these rocks indicate, are those of fire and water; and yet even here we find proof of system and intention, in the purpose which they have accomplished, of supplying and accumulating at the bottom of the water the materials of stratified formations, which in after times, were to be elevated into dry lands, in an ameliorated condition of fertility. Still more decisive are the evidences of design and method, which arise from the consideration of the structure and composition of their crystalline mineral ingredients. In every particle of matter to which crystallization has been applied, we recognise the action of those undeviating laws of polar forces, and chemical affinity, which have given to all crystallized bodies a series of fixt definite forms and definite compositions. Such universal prevalence of law, method, and order assuredly attests the agency of some presiding and controlling mind.

A farther argument, which will be more insisted on in speaking on the subject of metallic veins, may be founded on the dispensation whereby the primary and transition rocks are made the principal repositories of many valuable metals, which are of such peculiar and indispensable importance to mankind.

CHAPTER V.

Volcanic Rocks, Basalt, and Trap.

In the state of tranquil equilibrium which our planet has attained in the region we inhabit, we are apt to regard the foundation of the solid earth, as an emblem of duration and 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 farther 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 the mineral characters of these dikes 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.*

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 dikes 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 apparantly 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 uninhabita

• See Cordier on the internal temperature of the earth.

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