Biology: Geographical Distribution. Geological Distribution.
Living beings occupy portions of the surface of the earth, inhabiting either the dry land or the fresh or salt waters, or being competent to maintain their existence in either. In any given locality, it is found that those different media are inhabited by different types of living beings; and that the same medium, at different heights in the air and at different depths in the water, has different living inhabitants.
Moreover, the living populations of which differ considerably in latitude, and hence in climate, always present considerable differences. But the converse proposition is not true; if they resemble one another in climate, often have very dissimilar faunae and florae.
It has been discovered by careful comparison of local faunae and florae that certain areas of the earths surface are inhabited by groups of animals and plants which are not found elsewhere, and which thus characterize each of these areas. Such areas are termed Provinces of Distribution. There is no priority between these provinces in extent, nor in the physical configuration of their boundaries; and in reference to existing conditions, nothing can appear to be more arbitrary and capricious than the distribution of living beings.
The study of distribution is not confined to the present order of nature; but, by the help of geology, the naturalist is enabled to obtain clear, though too fragmentary, evidence of the characters of the faunae and florae of antecedent epochs. The remains of organisms which are contained in the stratified rocks prove that, in any given part of the earths surface, the living population of earlier epochs was different from that which now exists in the locality; and that, on the whole, the difference becomes greater the farther we go back in time. The organic remains which are found in the later Cainozoic deposits of any district are always closely allied to those now found in the province of distribution in which that locality is included; while in the older Cainozoic, the Mesozoic, and the Palaeozoic strata, the fossils may be similar to creatures at present living in some other province, or may be altogether unlike any which now exist.
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