IMPERFECTION OF GEOLOGICAL RECORD 81 



a distant epoch. Wherever sediment 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 secondary formations lie in the past, would gener- 

 ally be formed in the archipelago only during periods of 

 subsidence. These periods of subsidence would be sepa- 

 rated from eacb other by immense intervals of time, 

 during which the area would be either stationary or 

 rising; while 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, 

 sedimentary beds could hardly be accumulated of great 

 thickness during the periods of elevation, or become 

 capped and protected 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 eleva- 

 tion, 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 



rchipelago, together with a contemporaneous accumula- 



ion of sediment, would exceed the average duration of 



[the same specific forms; and these contingencies are 



ndispensable for the preservation of all the transitional 



jij Igradations between any two or more species. If such 

 jgradations were not all fully preserved, transitional 



