300 IMPEKFECTION OF THE Chap. IX. 



whole world in organic beings; yet if all the species 

 were to be collected which have ever lived there, how 

 imperfectly would they represent the natural history of 

 the world ! 



But we have every reason to believe that the terres- 

 trial productions of the archipelago would be preserved 

 in an excessively imperfect manner in the formations 

 which we suppose to be there accumulating. I suspect 

 that 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 pre- 

 served. 



In our archipelago, I believe that fossiliferous forma- 

 tions could be formed of sufficient thickness to last to 

 an age, as distant in futurity as the secondary forma- 

 tions lie in the past, only during periods of subsidence. 

 These periods of subsidence would be separated from 

 each other by enormous intervals, during which the 

 area would be either stationary or rising ; whilst rising, 

 each fossiliferous formation would be destroyed, almost 

 as soon as accumulated, by the incessant coast-action, as 

 we now see on the shores of South America. 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 least perfect. 



It may be doubted whether the duration of any one 

 great period of subsidence over the whole or part of 

 the archipelago, together with a contemporaneous accu- 

 mulation of sediment, would exceed the average duration 

 of the same specific forms ; and these contingencies are 



