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Show 252 IMPERFECTION OF THE [CHAP. IX. existed for millions of years as land, and thus have escaped the action of the sea: when deeply sttbmerged for perhaps equally long periods, it would, like~ise, have esc~p.ed the action of. the coast-waves. So that 1n all probab~hty a far longer period than 300 million years has elapsed s1nco the latter part of the Secondary period. . . . I have made these few remarks because It IS highly important for us to gain some notion, however imperfect, of the lapse of years. During each of these years, over the whole world, the land and the water has been peopled by hosts of living forms. What an infinite number of generations, which the mind cannot grasp, must have succeeded each other in the long roll of years I Now turn to our richest geological museums, and what a paltry display we behold! On the poorness of owr Palceontological collect~ons.That our palreontological collections are very imperf~ct, is adn1itted by every one. The remark of that admuable palreontologist, the late Edward Forbes, should not be forgotten, namely, that numbers of our _fossil species are known and na1ned from single and often broken specimens, or from a few specimens collected on some one spot. Only a small portion of the surface of the earth has been geologically explored, and no part with sufficient care, as the important discoveries made every year in Europe prove. No organism wholly soft can be preserved. Shells and bones will decay and disappear when left on the bottom of the sea, where sediment is not accumulating. I believe we are continually taking a most erroneous view, when we tacitly admit to ourselves that sediment is being deposited over nearly the whole bed of the sea, at a rate sufficiently quick to embed and preserve fossil remains. Throughout an enormously large proportion of the ocean, the bright blue tint of the water bespeaks its purity. The n1any cases on record of a formation conformably covered, ~.fter an enormous interval of time, by another and lat~r formation, without the underlying bed having suffered Ill the interval any wear and tear, seem explicable only on t~e view of the bottom of the sea not rarely lying for ages 111 0BAP. IX.] GEOLOGICAL RECORD. 2p3 an unaltered condition. The remains which do become em ·bedded, if in sand or gravel, will when the beds are upraised generally be dissolved by the percolation of rain-water. I suspect that but few of the very many animals which live on the beach between high and low watermark are preserved. For instance, the several species of the Chthamalinre (a sub-family of sessile cirripedes) coat the rocks all over the world in infinite numbers: they are all strictly l~ttoral, :vit~ the ~xception of a single Mediterranean speCies, whiCh Inhabits deep water and has been found fossil in Sicily, whereas not one other species has hitherto been found in any tertiary formation : yet it is now known that the genus Chthamalus existed during the chalk period. The molluscan genus Chiton offers a partially analogous case. With respect to the terrestrial productions which lived during the Secondary and Palreozoic periods, it is superfluous to state that our evidence from fossil remains is fragmentary in an extreme degree. For instance not a land shell is known belonging to ·either of the~e vast periods, with one exception discovered by Sir C. Lyell in the car?oniferous st~ata of ~ orth America. In regard to Inammiferous remains, a single glance at the historiral ta~le published in the Supplement to Lyell's Manual, will bring home the truth, how accidental and rare is their preservation, far better than pages of detail. Nor is their r~rity surprising, when we :emember how large a proportion of the bones of tertiary mammals have been discovered either in caves or i?- lacust~ine deposits; and that not a cave or true lacustrine bed 1s known belongino- to the age of our secondary or palreozoic formations. 5 But the imperfection in the geological record mainly results from a?-other and more important cause than any of .the foregoing; namely, from the several formations bmng separated from each other by wide intervals of time. When we see the formations tabulated in written works or ~h~n we follow them in nature, it is difficult to avoid believing that they are closely consecutive. But we kno":, for insta~ce from Sir R. Murchison's great work on Russia, what Wide gaps there are in that c<?untry between |
