The preservation of human remains depends mainly on the practice of burying the dead. Until the corpse is placed in a tomb protected by a stone coffin or dolmen, or in a grave dug in a cave, or otherwise sheltered from rains, floods, and wild beasts, the chances of its preservation are few and far between. Now it is not until the neolithic period that the custom of burying the dead became general, and even then it was not universal, and in many nations even in historical times corpses were burnt, not buried. It was connected doubtless with ideas of a future existence, which either required troublesome ghosts to be put securely out of the way, or to retain a shadowy existence by some mysterious connection with the body which had once served them for a habitation. Such ideas, however, only come with some advance of civilization, and it is questionable whether in palæolithic times the human animal had any more notion of preserving the body after death than the other animals by which he was surrounded. This neolithic habit moreover of burying, though it preserves many relics of its own time, increases the difficulty when we come to deal with those of an earlier age. A great many caves which had been inhabited by palæolithic man were selected as fitting spots for the graves of their neolithic successors, and thus the remains of the two periods became intermixed. It is never safe to rely on the antiquity of skulls and skeletons found in association with palæolithic implements and extinct animals, unless the exploration has been made with the greatest care by some well-known scientific observer, or the circumstances of the case are such as to preclude the possibility of later interments. Thus in the famous cavern of Aurignac there is no doubt that it had been long a palæolithic station, and that many of the human remains date back to this period; but whether the fourteen skeletons which were found in it, and lost owing to the pietistic zeal of the Mayor who directed their burial, were really palæolithic, is a disputed point, or rather the better opinion is that they were part of a secondary neolithic interment.