It is not believed that any
general or universal destruction of life took place at the
termination of each geological period, or that a general introduction
of new forms took place at the commencement of a new period.
It is, on the contrary, believed that the animals and plants
of any given period are for the most part (or exclusively) the
lineal but modified descendants of the animals and plants of
the immediately preceding period, and that some of them, at any
rate, are continued into the next succeeding period, either
unchanged, or so far altered as to appear as new species. To
discuss these views in detail would lead us altogether too far,
but there is one very obvious consideration which may advantageously
receive some attention. It is obvious, namely, that the great
discordance which is found to subsist between the animal life of
any given formation and that of the next succeeding formation,
and which no one denies, would be a fatal blow to the views just
alluded to, unless admitting of some satisfactory explanation.
Nor is this discordance one purely of life-forms, for there is
often a physical break in the successions of strata as well.
Let us therefore briefly consider how far these interruptions
and breaks in the geological and palaeontological record can be
accounted for, and still allow us to believe in some theory of
continuity as opposed to the doctrine of intermittent and occasional
action.
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