hat flourished in early
geologic epochs. If, now, the modern fossiliferous deposits of Australia
were to be examined by one ignorant of the existing Australian Fauna;
and if he were to reason in the usual manner; he would be very unlikely
to class these deposits with those of the present time. How, then, can
we place confidence in the tacit assumption that certain formations in
remote parts of the Earth are referable to the same period, because the
organic remains contained in them display a certain community of
character? or that certain others are referable to different periods,
because the _facies_ of their Faunas are different?

"But," it will be replied, "in past eras the same, or similar, organic
forms were more widely distributed than now." It may be so; but the
evidence adduced by no means proves it. The argument by which this
conclusion is reached, runs a risk of being quoted as an example of
reasoning in a circle. As already pointed out, between formations in
remote regions the accepted test of equivalence is community of fossils.
If, then, the contemporaneity of remote formations is concluded from the
likeness of their fossils; how can it be said that similar plants and
animals were once more widely distributed, because they are found in
contemporaneous strata in remote regions? Is not the fallacy manifest?
Even supposing there were no such fatal objection as this, the evidence
commonly assigned would still be insufficient. For we must bear in mind
that the community of organic remains usually thought sufficient proof
of correspondence in time, is a very imperfect community. When the
compared sedimentary beds are far apart, it is scarcely expected that
there will be many species common to the two: it is enough if there be
discovered a considerable number of common genera. Now had it been
proved that throughout geologic time, each genus lived but for a short
period--a period measured by a single group of strata--something might
be inferred. But what if we learn that many of the same genera continued
to exist throughout enormous epochs, measured by several vast systems of
strata? "Among molluscs, the genera _Avicula_, _Modiola_, _Terebratula_,
_Lingula_, and _Orbicula_, are found from the Silurian rocks upwards to
the present day." If, then, between the lowest fossiliferous formations
and the most recent, there exists this degree of community; must we not
infer that there will probably often exist a great degree