Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.2): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

ON THK DELUGE. 681 as it were, of the earth, wliich was so general as to have occa- sioned a marked and unqualified record, as of an event well known to all. Many philosophers think that the world has a central region of surpassing heat, and that the greater part of the interior of the fflobe is in a state of incandescence, if not of fusion. That small portion which they call the crust of the earth is supposed to be the only cooled part ; and they differ merely as to the degree of fluidity in the central region. I take it for granted that they have duly estimated the moon's tendency to cause tides in a fluid mass, within her influence : — if there were no crust, of course she would cause such an effect, but a well hardened case, we must suppose, can resist any such movement in the central fluid mass. Upon the principle of the arch, it would be easier to imagine resistance to pressure from without than from within; but the case or crust of our globe must be so solid that it neither yields nor vibrates to an internal expansive force. This theory, however, is unsupported by any satisfactory evidence. Men of character and attainments have advocated it, although resting on conjecture : but when we look back along the roll of history, and discover so few philosophers who have not greatly erred, although famed in their day, it is natural to pause, and not acquiesce hastily in mere human assertion unsubstantiated by proof. Boring the ground, or examining the temperature of the bottom of a deep mine, affords no estimate for that of the central regions : — Sir John Herschel says,* that " the deepest mine existing does not penetrate half a mile below the surface ; a scratch or pin- hole duly representing it on the surface of such a globe, (six- teen inches in diameter), would be imperceptible without a magnifier." As our globe is about eight thousand miles in diameter, and external influence may be supposed to penetrate some distance, we can draw but unsatisfactory conclusions from experiments at depths not nearly so great even as that to which -* Treatise on Astronomy; Cabinet Cyclopsedia, p. 22, Art. 30»