I will now direct the attention of scientists to a previously unnoticed cause which brings about the metamorphosis and decomposition phenomena which are usually called decay, putrefaction, rotting, fermentation and moldering. This cause is the ability possessed by a body engaged in decomposition or combination, i.e. in chemical action, to give rise in a body in contact with it the same ability to undergo the same change which it experiences itself.

The idea that the bumps or depressions on a man's head indicate the presence or absence of certain moral characteristics in his mental equipment is one of the absurdities developed from studies in this field that has long since been discarded by science. The ideas of the phrenologist Gall, however ridiculous they may now seem in the light of a century's progress, were nevertheless destined to become metamorphosed into the modern principles of cerebral localization.

The primary rocks, … I regard as the deposits of a period in which the earth’s crust had sufficiently cooled down to permit the existence of a sea, with the necessary denuding agencies,—waves and currents,—and, in consequence, of deposition also; but in which the internal heat acted so near the surface, that whatever was deposited came, matter of course, to be metamorphosed into semi-plutonic forms, that retained only the stratification. I dare not speak of the scenery of the period. We may imagine, however, a dark atmosphere of steam and vapour, which for age after age conceals the face of the sun, and through which the light of moon or star never penetrates; oceans of thermal water heated in a thousand centres to the boiling point; low, half-molten islands, dim through the log, and scarce more fixed than the waves themselves, that heave and tremble under the impulsions of the igneous agencies; roaring geysers, that ever and anon throw up their intermittent jets of boiling fluid, vapour, and thick steam, from these tremulous lands; and, in the dim outskirts of the scene, the red gleam of fire, shot forth from yawning cracks and deep chasms, and that bears aloft fragments of molten rock and clouds of ashes. But should we continue to linger amid a scene so featureless and wild, or venture adown some yawning opening into the abyss beneath, where all is fiery and yet dark,—a solitary hell, without suffering or sin,—we would do well to commit ourselves to the guidance of a living poet of the true faculty,—Thomas Aird and see with his eyes.

The swift metamorphosis and the onward march of civilization, sweeping ever westward and transforming and taming our wilderness, fills us with a strange regret, and we rejoice that parts of that wilderness will yet remain to us unchanged

We may therefore say in the future, strictly within the limits of observation, that in certain respects the fossil species of a class traverse in their historical succession metamorphoses similar to those which the embryos undergo in themselves. … The development of a class in the history of the earth offers, in many respects, the greatest analogy with the development of an individual at different periods of his life. The demonstration of this truth is one of the most beautiful results of modern paleontology.