all these organs would, on the
Darwinian theory, have slowly built up their different perfections and
complexities) occupied time at least a hundredfold greater.

Now it will be a moderate computation to allow 25,000,000 years for the
deposition of the strata down to and including the Upper Silurian. If,
then, the evolutionary work done during this deposition, only represents a
hundredth part of the sum total, we shall require 2,500,000,000 (two
thousand five hundred million) years for the complete development of the
whole animal kingdom to its present state. Even one quarter of this,
however, would far exceed the time which physics and astronomy seem able to
allow for the completion of the process.

Finally, a difficulty exists as to the reason of the absence of rich
fossiliferous deposits in the oldest strata--if life was then as abundant
and varied as, on the Darwinian theory, it must have been. Mr. Darwin
himself admits[141] "the case at present must remain inexplicable; and may
be truly urged as a valid argument against the views" entertained in his
book.

Thus, then, we find a wonderful (and on Darwinian principles an all but
inexplicable) absence of minutely transitional forms. All the most marked
groups, bats, pterodactyles, chelonians, ichthyosauria, anoura, &c., appear
at once upon the scene. Even the horse, the animal whose pedigree has been
probably best preserved, affords no conclusive evidence of specific origin
by infinitesimal, fortuitous variations; while some forms, as the
labyrinthodonts and trilobites, which seemed to exhibit gradual change, are
shown by further investigation to do nothing of the sort. As regards the
time required for evolution (whether estimated by the probably minimum{143}
period required for organic change or for the deposition of strata which
accompanied that change), reasons have been suggested why it is likely that
the past history of the earth does not supply us with enough. First,
because of the prodigious increase in the importance and number of
differences and modifications which we meet with as we traverse
successively greater and more primary zoological groups; and, secondly,
because of the vast series of strata necessarily deposited if the period
since the Lower Silurian marks but a small fraction of the period of
organic evolution. Finally, the absence or rarity of fossils in the oldest
rocks is a point at present inexplicable, and not to be forgotten or
neglected.