The careful observations and the acute reasonings of the Italian geologists of the seventeenth and eighteenth centuries; the speculations of in the 'Protogaea' and of in his 'Théorie de la Terre;' the sober and profound reasonings of , in the latter part of the eighteenth century; all these tended to show that the fabric of the earth itself implied the continuance of processes of natural causation for a period of time as great, in relation to human history, as the distances of the heavenly bodies from us are, in relation to terrestrial standards of measurement. The abyss of time began to loom as large as the abyss of space. And this revelation to sight and touch, of a link here and a link there of a practically infinite chain of natural causes and effects, prepared the way, as perhaps nothing else has done, for the modern form of the ancient theory of evolution.