420 Formation during Subsidence paet ii. 



strata. In how few parts of the world, probably, do 

 these conditions at the present day concur ! We can 

 thus, also, understand the general want of that close 

 sequence in fossiliferous formations which we might 

 theoretically have anticipated ; for, without we suppose 

 a subsiding movement to go on at the same spot during 

 an enormous period, from one geological era to another, 

 and during the whole of this period sediment to accu- 

 mulate at the proper rate, so that the depth should not 

 become too great for the continued existence of mollus- 

 cous animals, it is scarcely possible that there should be 

 a perfect sequence at the same spot in the fossil shells 

 of the two geological formations. 1 So far from a very 

 long-continued subsidence being probable, many facts 

 lead to the belief that the earth's surface oscillates up 

 and down ; and we have seen that during the elevatory 

 movements there is but a small chance of durable fos- 

 siliferous deposits accumulating. 



Lastly, these same considerations appear to throw 

 some light on the fact that certain periods appear to 

 have been favourable to the deposition, or at least to 

 the preservation, of contemporaneous formations at very 

 distant points. We have seen that in South America 

 an enormous area has been rising within the recent 

 period; and in other quarters of the globe immense 

 spaces appear to have risen contemporaneously. From 

 my examination of the coral-reefs of the great oceans, 



Professor H. D. Rogers, in his excellent address to the Associa- 

 tion of American Geologists (Siliiman's 'Journal,' vol. xlvii. p. 277), 

 makes the following remark : ' I question if we are at all aware how 

 completely the whole history of all departed time lies indelibly re- 

 corded with the amplest minuteness of detail in the successive 

 sediments of the globe, how effectually, in other words, every 

 period of time has written its own history, carefully preserving every 

 create*! form and every trace of action.' I think the correctness of 

 such remarks is more than doubtful, even if we except (as I suppose 

 he would) all those numerous organic forms which contain no hard 

 parts. 



