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Show 28t EXPLANATIONS. cultivators of science should allow themselv&s to follow the dictates of ·reason, against the 'behests of prejudicei unworthy of them and of their age. TIME is the true key to difficulties regarding appearances of determinateness in species. Few of us, not even g_eologis~s, have ever real~zed in our J:?in~s the ~xtent of time whiCh has elapsed s1nce the begtnrnng of hfe upon this globe. Mr. Lyell, ·without intending to favor the development theory, _lends us power_ful testimony on. this point. After showtng reason to believe that about thutyfive thousand years have passed since the Niagara began to cut down the rock through \Vhich it flows, during which time the living mollusks, whether tnarine or terrestrial, are proved to have undergone no change, he thus proceeds -"If such events can take place, ·while the zoology of the earth remains almost stationary and unaltered, what ages may not be comprehended in those successive tertiary periods during which the Flora and Fauna of the glo~e have been almost entirely changed! Yet how subordinate a place in the long calendar of geological chronology do the successive tertiary periods themselves occupy! How much more enormous a duration must we assign to many antecedent revolutions of tJ:e earth and its inhabitants! No analogy can be f~u~~ 1n the natur_al world to the immense scale of these diVISIOns of past bme, unless we contemplate the celestial spaces which have ~een measured by the astronomer. Some of the nearest of these within the limits of the solar system, as, for example, t~e orbits of the planets, are reckoned by hundreds of millions of miles, which the imagination in vain e~deavors to gra p. Yet one of these space , such as ~he dtame~er of the earth's orbit, is regarded as a 1ne~·e urut, a 1nere 1nfin· itesimal fraction of the distance which separates our sun from the neare t star. By pursuing still fur~ her the same inve tigations, we learn that there are lumtnous clouds, carcely di -- tin ruishable by the naked eye_, but resolvable by the tele cope into _lusters of stars, wh1ch are so ~t.~ch n1ore remote, that the tnter~al between our sun and S1~1us may be but a fraction of thi~ lar~er distance. T~ 1·e-gwns of pace of this higher order in point of 1nag_n1tude, we may, probably, compare such an interval of. ~tmt as that which d1vides the htunan poch fran~ the on.gtn of t~Le cod ralline linle tone, over 'Which the J'-lt agara ts prectp1tate TIME NECESSARY. 283 tJt the Falls. Many have been the successive ~evoluhons in organic life, and many the vicissitudes in the physical ~eography of the globe, and often has sea been converted tnto land since that rock was forVled. The Alps, the Pyrenees, the Himalaya, have not only begun to exist as lofty mountain chains, but the solid materials of which they a'.'e composed have been slowly elaborated beneath the sea within the stupendous interval of ages here alluded to."* If time, to anything like the amount here insisted on, have really elapsed between the commencement of life and its attaining its highest form~, we must see that the space comprised by the life of an individual, or even that longer portion during which mankind have been watching the wonders of nature, is not sufficient to allow more than a chance of any transition of species being or having been observed, except perhaps in the humble fields where, as ·was formerly remarked, reproduction is most active and type3 least defined. If, however, even in our limited command of this grand element, we can detect such transitions as those amongst the cerealia, or in a common infusion, may we not well suppose that much greater have taken place in the course of the vast series of ages here described? Absolute proof on such a point may be impossible; but nearly the same effect may be reached, if we see vestiges of the supposed facts in living phenomena, just as we conclude upon the formation of stratified and igneous rocks ft·om seeing similar phenomena, gen .. erally on a smaller scale, biking place before our eyes. There is another morle of attaining the means of a tolerably definite conclusion, where perfect ~0of is unattainable. This is to show a portion or fraction of the entire phenomenon, in conformity with the hypothesis as to the whole. Now this can be done in the case under consideration. There are isolated parts of the earth, which we know to have become dry land more recently than others. Such is the Galapagos. group of islands, situated in the Pacific, between five and six hundred miles from the American coast. They are wholly of volcanic origin, and are considered by Mr. Da1:win as having been raised out of the sea " within a late geological period .'• Here, then, is a piece of the world undoubtedly younger, so to speak, than most other portions are in their totality • • Travels in North America, i., 5~ |