OCR Text |
Show 186 EFFECTS OF THE POWERS OF VITALITY [Ch. XII. of some river, and with mineral matter precipitated from the waters of springs, the character of the deposits may be modified by aquatic animals and plants, which may convert the earthy particles into shell, peat, and other substances : but the lake may, nevertheless, be filled up in the same time, and the new strata may be deposited in nearly the same order as would have prevailed if its waters had never been peopled by living beings. In treating of the first division of our subject we may remark, that when we talk of alterations in physical geography, we are apt to think too exclusively of that part of the earth's surface which has emerged from beneath the waters, and with which alone, as terrestrial beings, we are familiar. Here the direct power of animals and plants to cause any important variations is, of necessity, very limited, except in checking the progress of that decay of which the land is the chief theatre. But if we extend our views, and instead of contemplating the dry land we consider that larger portion which is assigned to the aquatic tribes, we discover the immediate influence of the living creation, in imparting varieties of conformation to the solid exterior which the sole agency of inanimate causes would not produce, to be very great. Thus, when timber is floated into the sea, it is often dt·ifted to vast distances and subsides in spots where there might have been no deposit, at that time and place, if the earth had not been tenanted by living beings. If, therefore, in the course of ages, a hill of wood, or lignite, be thus formed in the subaqueous regions, a change in the submarine geography may be said to have resulted from the action of organic powers. So in regard to the growth of coral reefs: it is probable that almost all the matter of which they are composed is supplied by mineral springs, which we know often rise up at the bottom of the sea, and which, on land, abound throughout volcanic regions thousands of miles in extent. The matter thus constantly given out could not go on accumulating for ever in the waters, but would be precipitated in the abysses of the sea, even ~f there were no polyp~ and testacea; but these animals arrest Ch.XII.] ON THE STATE OF THE EARTll'S SURFACE. 187 and secrete the carbonate of 1I. me on the su 't f b · mountains and i' mm1 so su marme ' lOrm reefs many h d d i' • hundreds of Ieag · 1 un re 1eet m thickness, and ues m enoth h b i' ever have existed. 5 'w ere, ut wr them, none might If no such voluminous masses are [I not from the want of sol'd . armed on the land, it is . t matter m th t trial animals and plant b e s ructure of terres-s, ut merely b 1 often stated the c t' ecause, as we 1ave so ' on Inents are those f accessions of matt parts 0 the globe where er can scarcely ever k the contrary, the most I'd ta e place,-where, on . so 1 parts alread £ d . their turn, exposed t . d 1 . Y orme are, each m o gt a ua degradat Th timber and veoo- etab]e matt er wh 'I c h growIso n.' e q.u antity of in the course of a cent . m a tropiCal forest . ury Is enormous d 1 . a. mmal skeletons are scattere d th ere . ' an m u titudes of In the sa . d b . Innumerable ]and-shell s aQ d ot h er org · meb peno , es1des aggregate of these mat . I . h a.mc su stances. The ena s mig t constitute h greater in volume than th a t Wh I'C h I.S prod ' pde r. aps, a mass reef during .the same 1 f uce m any coral ... apse o years. b t I h h . should continue on the I d .e ' u 'a t oug this process an lOr ever no t . bone would be seen str t h' i' ' moun ams of wood or e c mg 1ar and 'd or pushing out bold promo t . . . WI e over the country' Th . . n ones Into the sea. d e whole sohd mass is either devoured by . 1 ecomp d amma s or tl . oses, as oes a portion of the rock and soil on h. 1 1e- ammals and plants are su o t w IC l sition of the strata th I PP r ed.. For the decompo-ingredients and of tl emse v.es, esp~cially of their alkaline 1e orgamc rem a h · h quently include I·s one f ms w Ic they so fre- the atmos here' so. urce rom h . w ence runnmg water and by the roo~s and ]:::e::;Iv~ t~e :,aterials which are absorbed into a gaseous form of e!:~hs. h no.ther source is the passage plants which die d e ardest parts of animals and an are exposed to t f · they are soon resolved i t th 1 pu re y m the air, where posed. and h'l n ~ e e ements of which they are com- ' w 1 e a portiOn of th · rest is taken up b . ese parts IS volatilized the Y ram-water and · k · ' towards the sea s th h sm s mto the earth or flows ' o at t ey enter a . d . composition of d'ffi . . gam an agam into the 1 ere~t orgamc bemgs. |