Palaeontology, then, is the science which treats of the living
beings, whether animal or vegetable, which have inhabited the earth
during past periods of its history. Its object is to elucidate,
as far as may be, the structure, mode of existence, and habits
of all such ancient forms of life; to determine their position
in the scale of organised beings; to lay down the geographical
limits within which they flourished; and to fix the period of
their advent and disappearance. It is the ancient life-history
of the earth; and were its record complete, it would furnish
us with a detailed knowledge of the form and relations of all
the animals and plants which have at any period flourished upon
the land-surfaces of the globe or inhabited its waters; it would
enable us to determine precisely their succession in time; and
it would place in our hands an unfailing key to the problems of
evolution. Unfortunately, from causes which will be subsequently
discussed, the palaeontological record is extremely imperfect,
and our knowledge is interrupted by gaps, which not only bear
a large proportion to our solid information, but which in many
cases are of such a nature that we can never hope to fill them
up.
Fossils.--The remains of animals or vegetables which we now find
entombed in the solid rock, and which constitute the working
material of the palaeontologist, are termed "fossils,"[3] or
"petrifactions.
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