Geology Reference
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upon a view of species as entities, not tendencies; things, not arbitrary
segments of a flux. Species arise at particular times in particular regions. They
are, if you will, particles with a definite point of origin, an unchanging
character during their geological duration, and a clear moment of extinction.
Most important, they are particles in a world of time's stately cycle. Their
origins and extinctions are not clumped in episodes of mass dying or explosive
radiation, but more or less evenly distributed through time, with births
balancing deaths to maintain an approximate constancy in
Figure 4.5
A modern example of destruction by erosion. The Grind of the Navir (the
breach between the two sections of this sea cliff in the Shetland Islands) is
widened every winter by the surge passing between. (From first edition of
Lyell's Principles. )
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