That such migrations can and do take place is quite
certain, and this is a much more reasonable explanation of the
observed facts than the hypothesis that in former periods the
conditions of life were much more uniform than they are at present,
and that, consequently, the same organisms were able to range over
the entire globe at the same time. It need only be added, that
taking the evidence of the present as explaining the phenomena
of the past--the only safe method of reasoning in geological
matters--we have abundant proof that deposits which _are_ actually
contemporaneous, in the strict sense of the term, _do not contain
the same fossils, if far removed from one another in point of
distance_. Thus, deposits of various kinds are now in process of
formation in our existing seas, as, for example, in the Arctic
Ocean, the Atlantic, and the Pacific, and many of these deposits
are known to us by actual examination and observation with the
sounding-lead and dredge. But it is hardly necessary to add that
the animal remains contained in these deposits--the fossils of some
future period--instead of being identical, are widely different
from one another in their characters.
We have seen, then, that the entire stratified series is capable of
subdivision into a number of definite rock-groups or "formations,"
each possessing a peculiar and characteristic assemblage of fossils,
representing the "life" of the "period" in which the formation
was deposited.
Pages:
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103