As we trace the history of birds back in time, we find their remains,
sometimes in great abundance, throughout the whole extent of the
tertiary rocks; but, so far as our present knowledge goes, the birds of
the tertiary rocks retain the same essential characters as the birds of
the present day. In other words, the tertiary birds come within the
definition of the class constituted by existing birds, and are as much
separated from reptiles as existing birds are. Not very long ago no
remains of birds had been found below the tertiary rocks, and I am not
sure but that some persons were prepared to demonstrate that they could
not have existed at an earlier period. But in the course of the last few
years, such remains have been discovered in England; though,
unfortunately, in so imperfect and fragmentary a condition, that it is
impossible to say whether they differed from existing birds in any
essential character or not. In your country the development of the
cretaceous series of rocks is enormous; the conditions under which the
later cretaceous strata have been deposited are highly favourable to the
preservation of organic remains; and the researches, full of labour and
risk, which have been carried on by Professor Marsh in these cretaceous
rocks of Western America, have rewarded him with the discovery of forms
of birds of which we had hitherto no conception.
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