World-life; or, Comparative geology . taryor super-crust. This process may continue during thewhole of the planets refrigerating history, though at notime can the encroachment at the bottom quite equal thesedimentary additions at the surface; since because theplanet is necessarily cooling as a mass, its crust must ex-perience a net increase of thickness. The final result * This idea seems to have been first shadowed forth almost simultaneouslyby Professor Charles Babbage and Sir John Herschel, in 1836, 1837 and 1838 (seeNinth Bridgewater Treatise, App. G; also London and Edinb. Phil. Mag.,
World-life; or, Comparative geology . taryor super-crust. This process may continue during thewhole of the planets refrigerating history, though at notime can the encroachment at the bottom quite equal thesedimentary additions at the surface; since because theplanet is necessarily cooling as a mass, its crust must ex-perience a net increase of thickness. The final result * This idea seems to have been first shadowed forth almost simultaneouslyby Professor Charles Babbage and Sir John Herschel, in 1836, 1837 and 1838 (seeNinth Bridgewater Treatise, App. G; also London and Edinb. Phil. Mag., ). Sir Johns suggestions are embodied in the Ninth Bridgewater Treatise,App. I, in three letters, dated Feb. and Nov., 1836, and June, 1837. See alsoLeouhards Jahrbuch, 1838, 98; 1839, 347. 276 A COOLIXG PLAXET. might be that sedimentary beds, accumulated even afterthe dawn of the organic epoch, might come to occupy thelowest position. Organic forms comparatively high mightseem to begin the succession of life by holding position in. Fig, 47.—Ascent of Isothermal Planes ix a Planets Crust. the oldest accessible rocks. Thus the palicontological in-vestigator would be foiled by an illusion. These changes are illustrated by the accompanying dia-gram. Figure 47. The line c c represents the bottom of TRANSFORMATIONS OF THE PLANETARY CRUST. 277 the sea, on which sediments are in process of some circumstances the ocean basin would thusundergo a process of filling, and the sea-bottom c c wouldoccupy successively higher positions. This would be thecase if the general configuration of the planetary crustwere to remain unchanged, the material deposited in thesea being only the amount removed from the land. Inmost cases, however, slow wrinkling would be in progress,so that the oceans bottom would suffer a gradual subsid-ence. Let us assume that the bottom c c remains at aconstant level notwithstanding sedimentary accumulation,the sinking being equal to the amount of s
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