Everywhere the tertiary fossils are closely analogous to existing types; but in all countries the fossils of the primary strata appear to belong to a very different series. Wherever the systems of European strata can be paralleled,—in North America—the Himalaya—Australia—so much of analogy is evident in the organic reliquiæ, as to prove that the successive changes of physical conditions, and the coincident changes of organic life, were operated over very large parts of the globe; and nothing, yet known, forbids us to believe that they were universally felt, though in unequal degrees, and under differences of circumstances.
Could we suppose produced on the present globe some general change of conditions in the sea, on the land, and in the atmosphere—either simultaneously, or by communication from a central area of disturbance —the effects upon organic life might be everywhere manifested, though unequally and variously. The extinction of some tribes, the decrease or enlargement of others—the creation of new types to fill the void spaces of creation, and be adapted to the new conditions, might seem to us quite in harmony with the designs of providence, and fully in accordance with past geological effects. There would, however, be this difference in the cases:—the races of animals and plants of this modern period of the globe are more various in different countries than the fossils of any one older geological period appear to have been; there is now more of local diversity in organic life upon the globe, than formerly obtained; and from this we infer that the physical conditions of the globe in former periods were more general —more uniform over large areas than at present. This character of uniformity among the organic contents of a system of strata, augments continually from the modern period toward the older, and is greatest among the most ancient strata, whose organic contents, though less numerous, are more similar in all countries yet explored than those of later date.
Since it thus appears that general laws of variation
