are no longer in activity, at least in the conditions and forms in which they give rise to such products.

Such is the formation of granite. That rock is more extensive, exists in greater volume, and fills and has filled a more important office in respect to the sedimentary strata, than any other in the series. It is far the greatest and the most significant of the effects that are the subject of geological inquiry. It wraps, it is generally believed, the whole circle of the globe, and is the basis on which all the other formations rest; and it has come into existence, or received its present form, at least to a vast extent, since the formation of large portions of the rocks which now repose on it. Those masses of it indisputably which rise above the original level of the sedimentary rocks, and form the centres of the great mountain ranges, were formed and elevated into their present positions after the deposition of the strata that lie on their summits, or rest on their sides, and they are now accordingly referred by geologists generally to the close of the secondary, or to the tertiary period.

But no granite, so far as is known, is produced at the present time, nor has been since the formation of the masses that constitute the main element of the great mountain ranges, and were the instrument by which the sedimentary strata that clothe their sides, and rest on many of their heights, were thrown up. There is not the slightest proof, or probability even,

that a particle of it has been crystallized for ages. What the conditions are, indeed, that are essential to its formation, are not fully known. It is generally held to be the result of fusion; but what the precise combination of causes is, or what the circumstances are in which they must act in order to unite the ingredients of which it consists in the proportions and forms that constitute its peculiarities, there are no means in the present state of the science of determining.

The greatest and most important geological process that has ever taken place on the earth's surface, and that was wrought on its greatest scale at a late period in the formation of the sedimentary strata, is thus wholly unlike any that is now in progress, or has been for ages, and confutes therefore the theory that the forces by which the crust of the earth was formed and modified, exist and operate with the same energy, and give birth to the same species of effects, and on the same scale, at all periods.

Gneiss, also micaceous, chlorite, and argillaceous schist, quartz rock, and other species that belong to the first series of the stratified formations, are not now in the process of deposition, and have not been for ages, nor are there any indications that the causes from which they sprang are any longer in activity. These also, though not universal, like granite, are very extensive. They underlie very generally, as far

as is known, the secondary formation, and are, in many localities, of immense depth. They constitute proofs, therefore, as vast as they themselves are, that the geological forces by which the strata have been formed, do not act without intermission, and with an unvarying energy, and give birth to their effects at the same rate at all periods. If that were their law, these rocks, instead of being confined to the primary formation, would have been intermixed with the whole secondary and tertiary series, and would now be generating on as great a scale as they were in their own proper age. Can a more emphatic confutation be asked of the doctrine, that geological causes act at all periods with an unvarying energy?

Serpentine, greenstone, basalt, and nearly the whole series of trap rocks, also came into existence exclusively, so far as is known, at a period long past. They were first thrown up, it is generally held, after the completion of the primary series, and their epoch appears to have closed near the commencement of the tertiary. They were as manifestly the product of a limited period, and owed their existence to a condition of the globe that no longer exists, as the formation of granite, gneiss, quartz rock, old red sandstone, or any other rock, the production of which has ceased. To assume, as a self-evident proposition, that the causes by which these immense masses were thrown up from the unfathomable depths of the earth,

through the vast series of crystalline, primary, and secondary rocks, are still in uninterrupted activity, and giving birth on an unvarying scale to the same effects, and make that postulate the basis of a theory of the whole series of formations, is to offer a contradiction to fact that is not often exceeded in boldness and extravagance.

Sand, gravel, and pebbles, are still more important elements of the earth's crust, that owe their existence to causes that are no longer in activity. They not only form, in a great measure, the loose unstratified mass that lies on the surface of the globe, but enter very largely into the composition of the principal layers in every group of strata throughout the secondary and tertiary formations-sandstones of every class, many conglomerates, and the arenaceous forms of shale and limestone-and constitute not improbably one-third of the whole mass from the lowest to the last of the fossiliferous beds. And they were all formed undoubtedly by chemical forces at the points and at the time of their deposition from the ocean; as there are no known agents by which, had they originated elsewhere, they could have been distributed over such vast spaces, and immixed so equably in the strata in which they are imbedded. Had the materials of which they consist been originally derived, as geologists maintain, from granite continents, and borne down to the sea by rivers, they

still must have received their present form after their diffusion through the waters from which they were precipitated; as their structure is not now crystalline like that of the quartz, felspar, mica, and hornblende of granite, but granular and concretionary, and the product therefore of a wholly different chemical agency. Their formation is, accordingly, one of the greatest and most peculiar of which the surface of the earth has been the theatre. The number of particles, grains, pebbles, and stones of larger size, that belong to this class in single layers of moderate extent, transcends immeasurably our powers of enumeration, and can be grasped only by Omniscience. How infinite then is the multitude that constitute their whole mass! Many of the strata of which they are the principal ingredient, are spread over vast areas, and of great depth. Groups of the old red sandstone are in some localities three or four thousand feet in thickness. Yet every one of those grains and pebbles, small or large, is of itself a proof of the error of the doctrine that the causes by which they were produced are still in activity, and perpetually giving birth to similar formations. Not a particle of sand or gravel, not a solitary pebble or mass of larger size, like those which are imbedded in conglomerates, has been brought into existence for ages. The supposition is, as we have already shown, inconsistent with the conditions that are requisite to such concretions. The silex that is