Lectures on Evolution | Page 7

The circumstantial evidence in favour of a
murder having been committed, in that case, is as complete and as
convincing as evidence can be. It is evidence which is open to no doubt
and to no falsification. But the testimony of a witness is open to
multitudinous doubts. He may have been mistaken. He may have been
actuated by malice. It has constantly happened that even an accurate
man has declared that a thing has happened in this, that, or the other

way, when a careful analysis of the circumstantial evidence has shown
that it did not happen in that way, but in some other way.
We may now consider the evidence in favour of or against the three
hypotheses. Let me first direct your attention to what is to be said about
the hypothesis of the eternity of the state of things in which we now
live. What will first strike you is, that it is a hypothesis which, whether
true or false, is not capable of verification by any evidence. For, in
order to obtain either circumstantial or testimonial evidence sufficient
to prove the eternity of duration of the present state of nature, you must
have an eternity of witnesses or an infinity of circumstances, and
neither of these is attainable. It is utterly impossible that such evidence
should be carried beyond a certain point of time; and all that could be
said, at most, would be, that so far as the evidence could be traced,
there was nothing to contradict the hypothesis. But when you look, not
to the testimonial evidence--which, considering the relative
insignificance of the antiquity of human records, might not be good for
much in this case--but to the circumstantial evidence, then you find that
this hypothesis is absolutely incompatible with such evidence as we
have; which is of so plain and so simple a character that it is impossible
in any way to escape from the conclusions which it forces upon us.
You are, doubtless, all aware that the outer substance of the earth,
which alone is accessible to direct observation, is not of a
homogeneous character, but that it is made up of a number of layers or
strata, the titles of the principal groups of which are placed upon the
accompanying diagram. Each of these groups represents a number of
beds of sand, of stone, of clay, of slate, and of various other materials.
On careful examination, it is found that the materials of which each of
these layers of more or less hard rock are composed are, for the most
part, of the same nature as those which are at present being formed
under known conditions on the surface of the earth. For example, the
chalk, which constitutes a great part of the Cretaceous formation in
some parts of the world, is practically identical in its physical and
chemical characters with a substance which is now being formed at the
bottom of the Atlantic Ocean, and covers an enormous area; other beds
of rock are comparable with the sands which are being formed upon
sea- shores, packed together, and so on. Thus, omitting rocks of
igneous origin, it is demonstrable that all these beds of stone, of which

a total of not less than seventy thousand feet is known, have been
formed by natural agencies, either out of the waste and washing of the
dry land, or else by the accumulation of the exuviae of plants and
animals. Many of these strata are full of such exuviae--the so-called
"fossils." Remains of thousands of species of animals and plants, as
perfectly recognisable as those of existing forms of life which you meet
with in museums, or as the shells which you pick up upon the
sea-beach, have been imbedded in the ancient sands, or muds, or
limestones, just as they are being imbedded now, in sandy, or clayey, or
calcareous subaqueous deposits. They furnish us with a record, the
general nature of which cannot be misinterpreted, of the kinds of things
that have lived upon the surface of the earth during the time that is
registered by this great thickness of stratified rocks. But even a
superficial study of these fossils shows us that the animals and plants
which live at the present time have had only a temporary duration; for
the remains of such modern forms of life are met with, for the most part,
only in the uppermost or latest tertiaries, and their number rapidly
diminishes in the lower deposits of that epoch. In the older tertiaries,
the places of existing animals and plants are taken by other forms, as
numerous and diversified as those which live now in the same localities,
but more or less different from them; in the mesozoic rocks, these are
replaced by others yet more divergent