We must now call to mind that the geographical distribution of plants and animals was very different in the geological ages from what it is now. Down to a time not long antecedent to man, the same vegetation overspread every clime, and a similar uniformity marked the zoology. This is conceived by M. Brogniart, with great plausibility, to have been the result of a uniformity of climate, produced by the as yet unexhausted effect of the internal heat of the earth upon its surface; whereas climate has since depended chiefly on external sources of heat, as modified by the various meteorological influences. However the early uniform climate was produced, certain it is that, from about the close of the geological epoch, plants and animals have been dispersed over the globe with a regard to their particular characters, and specimens of both are found so isolated in particular situations, as utterly to exclude the idea that they came thither from any common centre. It may be asked,—Considering that, in the geological epoch, species are not limited to particular regions, and that since the close of that epoch, they are very peculiarly limited, are we to presume the present organisms of the world to have been created _ab initio_ after that time? To this it may be answered,—Not necessarily, as it so happens that animals begin to be much varied, or to appear in a considerable variety of species, towards the close of the geological history. It may have been that the multitudes of locally peculiar species only came into being after the uniform climate had passed away. It may have only been when a varied climate arose, that the originally few species branched off into the present extensive variety. A question of a very interesting kind will now probably arise in the reader’s mind—_What place or status is assigned to man in the new natural system_. Before going into this inquiry, it is necessary to advert to several particulars of the natural system not yet noticed. It is necessary, in particular, to ascertain the grades which exist in the classification of animals. In the line of the aves, Mr. Swainson finds these to be nine, the species pica, for example, being thus indicated:— Kingdom Animalia. Sub-kingdom Vertebrata. Class Aves. Order Incessores. Tribe Conirostres. Family Corvidæ. Sub-family Corvinæ. Genus Corvus. Sub-genus, or species Pica.