Page - 353 - in The Origin of Species

ABSENCE OF INTERMEDIATE VARIETIES 353 tremely imperfect manner in the formations which we sup- pose to be there accumulating. Not many of the strictly littoral animals, or of those which lived on naked submarine rocks, would be embedded; and those embedded in gravel or sand would not endure to a distant epoch. Wherever sedi- ment did not accumulate on the bed of the sea, or where it did not accumulate at a sufficient rate to protect organic bodies from decay, no remains could be preserved. Formations rich in fossils of many kinds, and of thickness sufficient to last to an age as distant in futurity as the sec- ondary formations lie in the past, would generally be formed in the archipelago only during periods of subsidence. These periods of subsidence would be separated from each other by immense intervals of time, during which the area would be either stationary or rising; whilst rising, the fossiliferous formations on the steeper shores would be destroyed, almost as soon as accumulated, by the incessant coast-action, as we now see on the shores of South America. Even throughout the extensive and shallow seas within the archipelago, sedi- mentary beds could hardly be accumulated of great thickness during the periods of elevation, or become capped and pro- tected by subsequent deposits, so as to have a good chance of enduring to a very distant future. During the periods of subsidence, there would probably be much extinction of life; during the periods of elevation, there would be much variation, but the geological record would then be less perfect. It may be doubted whether the duration of any one great period of subsidence over the whole or part of the archipel- ago, together with a contemporaneous accumulation of sedi- ment, would exceed the average duration of the same specific forms ; and these contingencies are indispensable for the pres- ervation of all the transitional gradations between any two or more species. If such gradations were not all fully pre- served, transitional varieties would merely appear as so many new, though closely allied species. It is also probable thatf^ each great period of subsidence would be interrupted by os- cillations of level, and that slight climatal changes would I intervene during such lengthy periods ; and in these cases the \ inhabitants of the archipelago would migrate, and no closely \ L—lie XI I