y a certain form of jaw is, as a rule,
constantly accompanied by the presence of marsupial bones, but simply
because experience has shown that these two structures are co-ordinated.

The settlement of the nature of fossils led at once to the next advance
of palaeontology, viz. its application to the deciphering of the history
of the earth. When it was admitted that fossils are remains of animals
and plants, it followed that, in so far as they resemble terrestrial, or
freshwater, animals and plants, they are evidences of the existence of
land, or fresh water; and, in so far as they resemble marine organisms,
they are evidences of the existence of the sea at the time at which
they were parts of actually living animals and plants. Moreover, in
the absence of evidence to the contrary, it must be admitted that the
terrestrial or the marine organisms implied the existence of land or
sea at the place in which they were found while they were yet living.
In fact, such conclusions were immediately drawn by everybody, from
the time of Xenophanes downwards, who believed that fossils were really
organic remains. Steno discusses their value as evidence of repeated
alteration of marine and terrestrial conditions upon the soil of Tuscany
in a manner worthy of a modern geologist. The speculations of De Maillet
in the beginning of the eighteenth century turn upon fossils; and Buffon
follows him very closely in those two remarkable works, the "Theorie
de la Terre" and the "Epoques de la Nature" with which he commenced and
ended his career as a naturalist.

The opening sentences of the "Epoques de la Nature" show us how
fully Buffon recognised the analogy of geological with archaeological
inquiries. "As in civil history we consult deeds, seek for coins, or
decipher antique inscriptions in order to determine the epochs of human
revolutions and fix the date of moral events; so, in natural history,
we must search the archives of the world, recover old monuments from the
bowels of the earth, collect their fragmentary remains, and gather into
one body of evidence all the signs of physical change which may enable
us to look back upon the different ages of nature. It is our only
means of fixing some points in the immensity of space, and of setting a
certain number of waymarks along the eternal path of time."

Buffon enumerates five classes of these monuments of the past history of
the earth, and they are all facts of palaeontology. In the firs