be taken to
represent approximately the period of substantially constant conditions
during which no considerable change would be brought about. Now, if one
thousand years may represent the period required for the evolution of the
species _S. nasalis_, and of the other species of the genus Semnopithecus;
ten times that period should, I think, be allowed for the differentiation
of that genus, the African Cercopithecus and the other genera of the family
Simiidae--the differences between the genera being certainly more than
tenfold greater than those between the species of the same genus. Again we
may perhaps interpose a period of ten thousand years' comparative repose.

For the differentiation of the families Simiidae and Cebidae--so very much
more distinct and different than any two genera of either family--a period
ten times greater should, I believe, be allowed than that required for the
evolution of the subordinate groups. A similarly increasing ratio should be
granted for the successive developments of the difference between the
Lemuroid and the higher forms of primates; for those between the original
primate and other root-forms of placental mammals; for those between
primary placental and implacental mammals, and perhaps also for the
divergence of the most ancient stock of these and of the monotremes, for in
all these cases modifications of structure appear to increase in complexity
in at least that ratio. Finally, a vast period must be granted for the
development of the lowest mammalian type from the primitive stock of the
whole vertebrate sub-kingdom. Supposing this primitive stock to have {140}
arisen directly from a very lowly organized animal indeed (such as a
nematoid worm, or an ascidian, or a jelly-fish), yet it is not easy to
believe that less than two thousand million years would be required for the
totality of animal development by no other means than minute, fortuitous,
occasional, and intermitting variations in all conceivable directions. If
this be even an approximation to the truth, then there seem to be strong
reasons for believing that geological time is not sufficient for such a
process.

The second question is, whether there has been time enough for the
deposition of the strata which must have been deposited, if all organic
forms have been evolved according to the Darwinian theory?

Now this may at first seem a question for geologists only, but, in fact, in
this matter geology must in some resp