ductio ad absurdum_ of the whole argument.

Professor Hughes[154] refers, as a case of rapid deposition of matter
akin to stalagmite, to the deposit of travertine in the old Roman
aqueduct of the Pont du Gard, near Avignon, where a thickness of
fourteen inches seems to have accumulated in about 800 years. Mr. J.
Carey has given in _Nature_, December 18, 1873, another instance where
a deposit 0.75 inch thick was formed in fifteen years in a lead mine
in Durham. Mr. W. B. Clarke in the same journal gives a case where in
a cave at Brixton, known as Poole's Hole, a deposit one eighth of an
inch in thickness was formed in six months. Such examples show how
unsafe it is to reason as to the rate of deposit in by-gone times, and
when climatal and local conditions may have been very different from
those at present subsisting.

In an able address before the biological section of the British
Association in 1876, Wallace adduces the following considerations as
bearing on these questions; and these are well worthy of attention as
showing that it is the necessities of evolution rather than of
geological facts that demand the assumption of a great antiquity for
man, and induce so many writers to accept any evidence for this,
however doubtful: (1) The great cerebral development of the so-called
Palaeolithic men, which shows no indications of graduating into
inferior races. (2) The great variety of the implements of these
ancient men, and the excellence of their carvings on bone and ivory,
point to a similar conclusion. (3) Man is not related to any existing
species of ape, but in various ways to several different species. (4)
There is an accumulation of evidence to show that the earliest
historical races excelled in many processes in the arts and in many
kinds of culture. He instances the wonderful mechanical and
engineering skill evidenced in the pyramids of Egypt in proof of this.
His conclusion is either that the origin of man by development from
apes must be pushed much farther back than any geologists at present
hold, and I may add far beyond any probable date, or that he must have
originated by some "distinct and higher agency"--which last is no
doubt the true conclusion.

Haeckel, in his recent work, the "History of Creation," sketches the
development of man from a monad, in twenty-two stages; but he has to
admit that stage twenty-first, or that of the "Ape-like man," nowhere
exists, either recent or fossil. He has to assume