countryside; ice grinding ceaselessly at the mountain top; peat filling up the shallow lake—­these are the chief factors which have gone to make the physical world as we now actually know it.  Land and sea, coast and contour, hill and valley, dale and gorge, earth-sculpture generally—­all are due to the ceaseless interaction of these separately small and unnoticeable causes, aided or retarded by the slow effects of elevation or depression from the earth’s shrinkage towards its own centre.  Geology, in short, has shown us that the world is what it is, not by virtue of a single sudden creative act, nor by virtue of successive terrible and recurrent cataclysms, but by virtue of the slow continuous action of causes still always equally operative.

Evolution in geology leads up naturally to evolution in the science of life.  If the world itself grew, why not also the animals and plants that inhabit it?  Already in the eager active eighteenth century this obvious idea had struck in the germ a large number of zoologists and botanists, and in the hands of Lamarck and Erasmus Darwin it took form as a distinct and elaborate system of organic evolution.  Buffon had been the first to hint at the truth; but Buffon was an eminently respectable nobleman in the dubious days of the tottering monarchy, and he did not care personally for the Bastille, viewed as a place of permanent residence.  In Louis Quinze’s France, indeed, as things then went, a man who offended the orthodoxy of the Sorbonne was prone to find himself shortly ensconced in free quarters, and kept there for the term of his natural existence without expense to his heirs or executors.  So Buffon did not venture to say outright that he thought all animals and plants were descended one from the other with slight modifications; that would have been wicked, and the Sorbonne would have proved its wickedness to him in a most conclusive fashion by promptly getting him imprisoned or silenced.  It is so easy to confute your opponent when you are a hundred strong and he is one weak unit.  Buffon merely said, therefore, that if we didn’t know the contrary to be the case by sure warrant, we might easily have concluded (so fallible is our reason) that animals always varied slightly, and that such variations, indefinitely accumulated, would suffice to account for almost any amount of ultimate difference.  A donkey might thus have grown into a horse, and a bird might have developed from a primitive lizard.  Only we know it was quite otherwise!  A quiet hint from Buffon was as good as a declaration from many less knowing or suggestive people.  All over Europe, the wise took Buffon’s hint for what he meant it; and the unwise blandly passed it by as a mere passing little foolish vagary of that great ironical writer and thinker.