Our hawks could not survive without wing-power or great speed, but the crow survives without this power, because he is an omnivorous feeder and can thrive where the hawk would starve, and also because no bird of prey wants him, and, more than that, because he is dependent upon nothing that requires speed to secure. He is cunning and suspicious for reasons that are not obvious. The fox in this country requires both speed and cunning, but in South America Darwin saw a fox so indifferent and unafraid that he walked up to it and killed it with his geologist's hammer. Has it no enemies in that country? Nature's course is always a roundabout one. Our petty economies are no concern of hers. Man wants specific results at once. Nature works slowly to general results. Her army is drilled only in battle. Her tools grow sharper in the using. The strength of her species is the strength of the obstacles they overcome. We misinterpret Darwin when we assume that Nature selects as man selects. Nature selects solely upon the principle of power of survival. Man selects upon the principle of utility. He wants some particular good--a race-horse, a draft-horse--better quality or greater quantity of this or that. Nature aims to fill the world with her progeny. Only power to win in the competition of life counts with her. As I have so often said, she plays one hand against the other. The stakes are hers whichever wins. Wheat and tares are all one to her. She pits one species of plant or animal against another--heads I win, tails you lose. Some plants spread both by seed and runners, this doubles their chances; they are kept in check because certain localities are unfavorable to them. I know a section of the country where a species of mint has completely usurped the pastures. It makes good bee pasturage, but poor cattle pasturage. Quack grass will run out other grass because it travels under ground in the root as well as above ground in the seed. XI. NATURAL SCULPTURE We may say that all the forms in the non-living world come by chance, or by the action of the undirected irrational physical forces, mechanical or mechanico-chemical. There are not two kinds of forces shaping the earth's surface, but the same forces are doing two kinds of work, piling up and pulling down--aggregating and accumulating, and separating and disintegrating.