REMARKS OX MR. DARWIN S THEORY. 



187 



seen that a thick fossiliferous formation can only be accumu- 

 lated during a period of subsidence ; and to keep the depth 

 approximately the same, which is necessary in order to enable the 

 same species to live on the same space, the supply of sediment mast 

 nearly have counterbalanced the amonnt of subsidence. But this 

 same movement of subsidence will often tend to sink the area whence 

 the sediment is derived, and thus diminish the supply whilst the down- 

 ward movement continues. In fact, this nearly balancing between 

 the supply of sediment and the amount of subsidence is probably a 

 rare contingency ; for it has been observed by more than one palae- 

 ontologist that very thick deposits are usually barren of organic 

 remains, except near their upper or lower limits"* 



We cannot, therefore, ever expect to fill up the gaps between dif- 

 ferent species and genera ; still, in point of fact, there is nothing like 

 " an entire absence of intermediate forms." All the fossils yet found 

 are intermediate ; and more than this, the older a form is the more 

 it usually differs from living forms, and the more general is its struc- 

 ture. Trilobites, for instance, are more like the larva? of living 

 crustaceans than like the crustaceans themselves. " Owen has shown 

 that the more generalized structure is, in a very significant degree, a 

 characteristic of many extinct, as compared with recent, animals ;"t 

 and Mr. Woodward remarks " that the last developed groups are 

 the most typical or characteristic of their class. "J 



Next, with regard to the second part of the geological argument, I 

 think that, remembering the imperfection of the geological record, 

 it is very rash to affirm that " because certain genera or families are not 

 found beneath a certain stage, therefore they did not exist before that 

 stage," an argument that is being disproved almost every month. 

 The progenitors of these genera may have lived long before, during 

 the intervals that exist between the different strata, and were most 

 likely developed during a period of elevation, and consequently when 

 no record was kept of the event ; but when the land became stationary 

 and the conditions of life more fixed they would multiply rapidly, 

 without much change, and spread far and wide : when a period of 

 subsidence came their remains would be buried, perhaps in large 

 quantities throughout the whole of the area over which they had 

 spread. Mr. Darwin has also remarked " that it might require a 

 long succession of ages to adapt an organism to some new and pecu- 

 liar line of life, for instance to fly through the air ; but when this had 

 been effected, and a few species had thus acquired a great advantage 

 over other organisms, a comparatively short time would be necessary 

 to produce many divergent forms, which would be able to spread 

 rapidly and widely throughout the world. "§ 



It was shown long ago that different fossils came from different 

 formations ; and now, acting on this, if forms differ ever so little, or 



* " On the Origin of Species," p. 295. 

 f Edinburgh Review, April, 1860, p. 507. 

 % " Recent and Fcssil Shells," p. 417. See also p. 4ia 

 § "On the Origin of Species," p. 303. 



