their way, as it were, in the bowels of the earth, and have
achieved only an imperfect and abortive development? It is easy
to sneer at our ancestors for being disposed to reject the first
in favour of one or other of the last two hypotheses; but it is
much more profitable to try to discover why they, who were
really not one whit less sensible persons than our excellent
selves, should have been led to entertain views which strike us
as absurd, The belief in what is erroneously called spontaneous
generation, that is to say, in the development of living matter
out of mineral matter, apart from the agency of pre-existing
living matter, as an ordinary occurrence at the present day--
which is still held by some of us, was universally accepted as
an obvious truth by them. They could point to the arborescent
forms assumed by hoar-frost and by sundry metallic minerals as
evidence of the existence in nature of a "plastic force"
competent to enable inorganic matter to assume the form of
organised bodies. Then, as every one who is familiar with
fossils knows, they present innumerable gradations, from shells
and bones which exactly resemble the recent objects, to masses
of mere stone which, however accurately they repeat the outward
form of the organic body, have nothing else in common with it;
and, thence, to mere traces and faint impressions in the
continuous substance of the rock. What we now know to be the
results of the chemical changes which take place in the course
of fossilisation, by which mineral is substituted for organic
substance, might, in the absence of such knowledge, be fairly
interpreted as the expression of a process of development in the
opposite direction--from the mineral to the organic. Moreover,
in an age when it would have seemed the most absurd of paradoxes
to suggest that the general level of the sea is constant, while