It is maintained, however, on the other hand, that the central caloric, however intense at any depth, has long ago arrived at the point at which the conducting power of the rocky crust has either entirely ceased or permits no further sensible decrease; that this point was reached some time before the creation of man, when the process of cooling had acquired a maximum or stationary condition, and that it formed a part of the processes by which the earth was adapted to its high destination among the works of God. But may not the adaptation have been effected by the gradual conduction of the heat outwardly, not by suffering it to remain and glow in opposition to its known properties in the inner regions? It may be maintained as a safe principle in physical science, that if there be heat in the center of the globe, it must have the properties of heat and none other. No geologist hesitates to admit, upon evidence amounting to demonstration, that a vast source of heat exists in the interior of the earth, widely spread beneath the stony pavement, and that it has existed at all times. But whether that heat is local or generally diffused—whether it is central or infra-superficial—whether it is constantly maintained, or is excited at intervals by certain combinations—are questions as yet of mere speculation, and for the solution of which we have no data to lead us, beyond probable inferences. Upon the whole, as the known density of the earth is considerably greater than that of a solid sphere, composed of any such rocks as we are acquainted with, the presumption is, that heavier materials, in an increasing ratio, than any constituting the superficial crust, enter into the composition and structure of the central parts. All the great mountain systems in the different zones of the globe are the product of palæozoic times. The fires which cast them out have gradually diminished by every succeeding effort. A steadier equilibrium betwixt the conflicting elements of the upper and the lower world, appears to have taken place—once only disturbed, at the deluge, since man’s occupation—and for the repetition of which there exists no preparation in the established course of nature. The very convulsions which have shattered the earth to its foundations, while they are evidences of benevolent wisdom, furnish, at the same time, the best guarantee against blind fortuitous derangements to come; the result, as they are, of periodical causes, acting in a way and with an intensity of which we have no experience, and for which, indeed, we have no expression in any of the sciences. GENERAL PRINCIPLES. PART IV. CHAPTER I. RÉSUMÉ.