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 



