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Show UNIFORMITY OF TilE SYSTEM. 166 . d l es which the deep·seatc vo cano 'than imacrc of those chang . Thus although we Wl o . . the nether regiOns. ' . d may now occasion m ~ f the planet, chame to . on the sunace o f . arc mere soJourners d . but for a moment o tlme, a mere po·m t m· s·p ace ' en urmbgl d to number wor ld s b eyon d the human mm. d . t only ena e . f . d lS no b t to trace the events o m C· the unassisted ken of mort~l eyef, ur race and is not even with· finite ages bel~o rc t1 reauon o ou ' h 1C c. h d rk secrets of the ocean, or t e held from pene t rat.i ng mto .t fe· a like the sp·l n· t wh I' c h t h e poe t . erior of the sohd globe' r.ee, ldnets cr1' be c l as animating the umverse, . - ire per omncs . ue rofundum. Terrasqu e tractusque mans, coolumq p CHAPTER X. Division of the subject into changes of the organic and inorganic world-lnor· ganic causes of change divided into the aqueous and igneous-Aqueous causes -Destroying and transporting power of running water-Sinuosities of rivers -Two streams when united do not occupy a bed of double surface-Heavy matter removed by torrents and floods-Recent inundations in ScotlandEfFects of ice in removing stones-Erosion of chasms through hard rocks-. Excavations in the lavas of Etna by Sicilian rivers-Gorge of the SimetoGradual recession of the cataracts of Niagara-Speculations as to the time required for their reaching Lake Erie~ WE defined geology to be the science which investigates the former changes that have taken place in the 9rganic, as well as in the inorganic kingdoms of nature ; and we now proceed to inquire what changes are now in progress in both these departments. Vicissitudes in the inorganic world are most apparent, and as on them all fluctuations in the animate creation must in a great measure depend, they may claim our :first consideration. We may divide the great agents of change in the inorganic world into two principal classes, the aqueous and the igneous. To the former belong Rivers, Torrents, Springs, Currents, and Tides; to the latter, Volcanos and Earthquakes, Both. these classes are instruments of decay as well as of reproduction; but they may be also regarded as antagonist forces. The aqueous agents are incessantly labouring to reduce the inequalities of the earth's surface to a level, while the igneous, on the other hand, are equally active in restoring the unevenness of the external crust, partly by heaping up new matter in certain localities, and partly by depressing one portion, and forcing out another of the earth's envelope. It is difficult, in a scientific arrangement, to give an accurate view of the combined effects of so many forces in simultaneous operation; because, when we consider them separately, we cannot easily estimate either the extent of their efficacy, or the kind of results which they produce. We are in * |
