considerable portion of the
thickness of the earth's crust contains faithful records of the past
forms of life, and inasmuch as these differ more and more as we go
further down,--it is possible and conceivable that we might come to
some particular bed or stratum which should contain the remains of those
creatures with which organic life began upon the earth. And if we did
so, and if such forms of organic life were preservable, we should have
what I would call historical evidence of the mode in which organic life
began upon this planet. Many persons will tell you, and indeed you will
find it stated in many works on geology, that this has been done, and
that we really possess such a record; there are some who imagine that
the earliest forms of life of which we have as yet discovered any
record, are in truth the forms in which animal life began upon the
globe. The grounds on which they base that supposition are these:--That
if you go through the enormous thickness of the earth's crust and get
down to the older rocks, the higher vertebrate animals--the quadrupeds,
birds, and fishes--cease to be found; beneath them you find only the
invertebrate animals; and in the deepest and lowest rocks those remains
become scantier and scantier, not in any very gradual progression,
however, until, at length, in what are supposed to be the oldest rocks,
the animal remains which are found are almost always confined to four
forms--'Oldhamia', whose precise nature is not known, whether plant or
animal; 'Lingula', a kind of mollusc; 'Trilobites', a crustacean animal,
having the same essential plan of construction, though differing in
many details from a lobster or crab; and Hymenocaris, which is also a
crustacean. So that you have all the 'Fauna' reduced, at this period,
to four forms: one a kind of animal or plant that we know nothing about,
and three undoubted animals--two crustaceans and one mollusc.

I think, considering the organization of these mollusca and crustacea,
and looking at their very complex nature, that it does indeed require a
very strong imagination to conceive that these were the first created of
all living things. And you must take into consideration the fact that
we have not the slightest proof that these which we call the oldest beds
are really so: I repeat, we have not the slightest proof of it. When you
find in some places that in an enormous thickness of rocks there are but
very scanty traces of life, or absolutely n