INTRODUCTION.

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countries of Europe , at present remote from any active volcanos.Such craters are found in Auvergne, on the Rhine betweenBonn and Andernach, in Hungary , and along the west side ofItaly, where Vesuvius alone still retains its energy. In allthese instances the fact that the currents of lava and showers ofashes have descended the present vallies, proves the activityof these volcanos subsequently to the complete excavation ofthose vallies.

Another actual cause of change operating on the surface ofthe planet, is one which we can scarcely include among geologi-cal phcenomena, and which it yet seems necessary to mentionin order to present a complete view of those changes: we alludeto the coral reefs and islets formed in the midst of the Pacificocean and some other seas, by the minute but combined laboursof millions of marine zoophytes. The following extract fromKotzebue’s voyages (as cited in the Quarterly Review) givesthe latest and perhaps the best view of this interesting subject.

u As soon as it [the ridge or reef] has reached such a height,that it remains almost dry at low water, at the time of ebb, thecorals leave off building higher; sea-shells, fragments of corals,sea hedge-hog shells, and their broken off prickles are unitedby the burning sun, through the medium of the cementing cal-careous sand, which has arisen from the pulverisation of theabove-mentioned shells, into ope whole or solid stone, which,strengthened by the continual throwing up of new materials,gradually increases in thickness, till it at last becomes so high,that it is covered only during some seasons of the year by thehigh tides. The heat of the sun so penetrates the mass of stonewhen it is dry, that it splits in many places, and breaks off inflakes. These (lakes, so separated, are raised one upon anotherby the waves at the time of high water. The always active surfthrows blocks of coral (frequently of a fathom in length, andthree or four feet thick) and shells of marine animals betweenand upon the foundation stones ; after this the calcareous sandlies undisturbed, and offers to the seeds of trees and plants castupon it by the waves, a soil upon which they rapidly grow toovershadow its dazzling white surface. Entire trunks of trees,which are carried by the rivers from other countries and islands,find here, at length, a resting place, after their long wander-ings: with these come some small animals, such as lizards andinsects, as the first inhabitants. Even before the trees form awood, the real sea-birds nestle here; strayed land-birds takerefuge in the bushes; and at a much later period, when thework has been long since completed, man also appears, buildshis hut on the fruitful soil formed by the corruption of the leaves