REMARKS ON MR. BARWIX'S THEORY. 
187 
seen that a thick fossiliferons 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 must 
nearly have counterbalanced the amount of subsidence. But this 
same movement of subsidence ^vill often tend to sink the area vrhence 
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 larvre of living 
crustaceans than like the crustaceans themselves. " Owen has sho-svn 
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 pai-t 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 : Avhen a period of 
subsidence came their remains would be bmned, 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 Hne 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 -sxddely 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. 
t Edinburgh Review, April, 1860, p. 507. 
X " flecent and Fcssil Shells," p. 117. See also p. 4ia 
§ " On the Origin of Species," p. 303. 
