182 WHEN THE WOULD WAS YOUNG
countries, and when the creatures became tired of eating soft things, they had only to uproot a tree, or tear off one of the branches, and crunch up the wood between their strong teeth. Of course, in African forests, the size of the trees often baffles even the strength of an elephant; but in northern climates, such as Siberia, few could stand against a mammoth, the weight of whose tusks commonly amounted to 320 lbs. 1
Now it seems wonderful to us that, after so many ages have passed, we can still find the skeletons of these animals, and, indeed, this can only happen in certain ways. In order to preserve a skeleton or even a whole body, it is absolutely needful that it should be kept shut off from either air or water, or not only its flesh, but its bones, will in time crumble away and vanish. This occurs when the animal dies above ground, or is drowned in some lake or river with a sandy, gravelly bottom; and in rocks made up of these substances we shall find but few fossils, or traces of plant and animal life. But if the bed of the lake should happen to be made of mud or clay, or something into which neither air nor water can penetrate, the body of the creature which has got stuck in swimming, or has been somehow caught fast and held, will gradually sink down till he is entirely covered. By-and-by the mud which wraps him round will have become solid rock, keeping within it one of the secrets of a world gone by. Peat will also preserve bodies that have fallen into it, to be dug out, ages after, fresh and young, andóin the case of men and womenówith even their clothes undecayed; but one of the most usual means of preservation consists in freezing the bodies, and thus excluding the air.
The great frozen marshes of the north of Siberia teem with remains of mammoths, which have either died on the spot or been carried down by the floods of the mighty rivers. In warm summers, or during heavy gales, these marshes become thawed or broken up, and sometimes one