"The destructive liquid currents before which the hardest mountains have been swept and comminuted into gravel, sand, and mud, which intervened between and divided these epochs, probably extending over the whole surface of the globe and destroying nearly all living things, must have reduced existence so much that an unoccupied field would be formed for new diverging ramifications of life, which from the connected sexual system of vegetables, and the natural instinct of animals to herd and combine with their own kind, would fall into specific groups--these remnants in the course of time moulding and accommodating their being anew to the change of circumstances, and to every possible means of subsistence--and the millions of ages of regularity which appear to have followed between the epochs, probably after this accommodation was completed, affording fossil deposit of regular specific character. . . . . . . "In endeavouring to trace ... the principle of these changes of fashion which have taken place in the domiciles of life the following questions occur: Do they arise from admixture of species nearly allied producing intermediate species? Are they the diverging ramifications of the living principle under modification of circumstance? or have they resulted from the combined agency of both? "_Is there only one living principle? Does organized existence, and perhaps all material existence, consist of one Proteus principle of life_ capable of gradual circumstance-suited modifications and aggregations without bound, under the solvent or motion-giving principle of heat or light? There is more beauty and unity of design in this continual balancing of life to circumstance, and greater conformity to those dispositions of nature that are manifest to us, than in total destruction and new creation. It is improbable that much of this diversification is owing to commixture of species nearly allied; all change by this appears very limited and confined within the bounds of what is called species; the progeny of the same parents under great difference of circumstance, might in several generations even become distinct species, incapable of co-reproduction.