136 
THE GEOLOGIST. 
24. Why the extinct fauna of a conntiy bears a close analogy to 
tlie living fauna. 
25. VThj the propoi-tion of species increases from the oldest forma- 
tions to the newest. 
26. Vfhj species were more widely distributed formerly than now; 
for as more species were developed, the more local they must 
have become. 
I know of no answers to these ai-guments ; they are simply facts 
acknowledged by everybody, except perhaps those for which I have 
given my authority. 
Taking everything then into consideration, I think that the evidence 
is greatly in favour of variation being at present unlimited.* 
The second argument against Mr. Darwin's theory is that natural 
selection, although allowed to be a " vera causa" of variation, is not 
powerful enough to produce the great differences that exist among or- 
ganic forms ; or, in other words, that the cause is not equal to the effect. 
The cause may be compared to the power of a machine that has to 
be increased or diminished according as the time in which it is re- 
quired to produce a given effect is shortened or lengthened. I believe 
that no one but a geologist has any conception of the enormous length 
of time comprehended in the term " geological period ;" and, although 
all or nearly all of my readers will be geologists, yet I think that it 
will perhaps be as well to try to get some very rough idea of it, 
especially as " time" has been brought forward in answer to other 
arguments. 
Mr. Darwin has shown that for long periods of geological time 
volcanic action has been pretty regular and persistent beneath Chili, 
and that the average elevation of the coast is about three feet in a 
centuiy :t but in the Pampean mud," in which the remains of 
Megatherium, Mylodon, &c., are found, is sometimes twelve thousand 
feet above the level of the sea ; this would make its age foui' hundred 
thousand yea'rs, yet it is only of Pleistocene age, and was formed 
perhaps since man inhabited the globe. How old then is the Phocene 
How old the Eocene ? How old the chalk ? Ten million years is the 
least that can represent it ; and yet it is not more than a twenty-fifth 
part of the thickness of the sedimentary strata of Great Britain. 
■In such an enormous time, then, how small may have been the cause 
of the gradual change of the lowest form of life into the highest ? — 
much less than a stmggle for life or death. 
* By at present nnlimited, I mean that there is no limit between the lowest 
and the highest kno\yn fonns of life, but beyond the highest there may be a limit 
to which vre are approaching. 
t Proceedings of the Geological Society, vol. ii,, p. 446, and Darwin's " Geology 
of South America." London: 1846. 
(To he Contimied.) 
