mission.] Supported by the facts
that have been mentioned respecting the later fossils of Australia and
Brazil, and their analogy to forms now existing in those countries, much
stress was laid on the hereditary transmission of structure, and hence
the inference was drawn that such examples are of a mixed nature,
depending in part on external agency, in part on an interior
developmental force. From marsupial animals, marsupials will issue; from
placental ones, those that are placental. But here, perhaps, an
illustration drawn from the inorganic kingdom may not be without
interest and use. Two pieces of carbonate of lime may be rolling among
the pebbles at the bottom of a brook, one perpetually splitting into
rhomboids, the other into arragonitic prisms. The fragments differ from
one another not only thus in their crystalline form, but in their
physical qualities, as density and hardness, and in their optical
qualities also. We might say that the calc-spar crystals gave birth to
calc-spar crystals, and the arragonitic to arragonite; we might admit
that there is an interior propensity, an intrinsic tendency to produce
that result, just as we say that there is a tendency in the marsupial to
engender a marsupial; but if, in our illustration, we look for the cause
of that cause, we find it in a physical impression long antecedently
made, that the carbonate of lime, crystallizing at 212 deg. Fahr.,
produces arragonite, and, at a lower temperature, calc-spar; and that the
physical impression thus accomplished, though it may have been thousands
of years ago, was never cast off, but perpetually manifested itself in
all the future history of the two samples. That which we sometimes speak
of as hereditary transmission, and refer to an interior property,
peculiarity, or force, may be nothing more than the manifestation of a
physical impression long antecedently made.

In the last place, the idea of an intrinsic force of development is in
connexion with time and a progression, and only comes into prominence
when we examine a limited portion or number of the things under
consideration. The earth, though very beautiful, is very far from being
perfect. [Sidenote: The broken organic chain.] The plants and animals we
see are only the wrecks of a broken series, an incomplete, and,
therefore, unworthy testimonial of the Almighty power. We should judge
very inadequately of some great author if only here and there a
fragmentary paragraph of h