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 first place, he says, shells and other marine productions
are found all over the surface and in the interior of the dry
land; and all calcareous rocks are made up of their remains.
Secondly, a great many of these shells which are found in Europe
are not now to be met with in the adjacent seas; and, in the
slates and other deep-seated deposits, there are remains of
fishes and of plants of which no species now exist in our
latitudes, and which are either extinct, or exist only in more
northern climates. Thirdly, in Siberia and in other northern
regions of Europe and of Asia, bones and teeth of elephants,
rhinoceroses, and hippopotamuses occur in such numbers that
these animals must once have lived and multiplied in those
regions, although at the present day they are confined to
southern climates. The deposits in which these remains are found
are superficial, while those which contain shells and other
marine remains lie much deeper. Fourthly, tusks and bones of
elephants and hippopotamuses are found not only in the northern
regions of the old world, but also in those of the new world,
although, at present, neither elephants nor hippopotamuses occur
in America. Fifthly, in the middle of the continents, in regions
most remote from the sea, we find an infinite number of shells,