333 AB8EN0E OF INTERMEDIATE VARIETIES 



productions of the archipelago would be preserved in an 

 extremely imperfect manner in the formations which we 

 suppose 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 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 thick- 

 ness sufficient to last to an age as distant in futurity as the 

 secondary formations lie in the past, would generally be 

 formed in the archipelago only during periods of subsi- 

 dence. 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; 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 daring 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 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 gxeat 

 period of subsidence over the whole or part of the archi- 

 pelago, together with a contemporaneous accumulation of 

 sediment, would exceed the average duration of the same 

 specific forms; and these contingencies are indispensable 

 for the' preservation of all the transitional gradations be- 

 tween any two or more species. If such gradations were 

 not all fully preserved, transitional varieties would merely 

 appear as so many new, though closely allied species. It 

 is also probable that each great period of subsidence would 

 be interrupted by oscillations of level, and that slight cli- 

 matical changes would intervene during such lengthy 

 periods; and in these cases the inhabitants of the archi- 



