A third method of dating the art is still more significant; it is through a similarity in the engravings on bone, found in the old hearths associated with flints, to the mural decorations which are found upon the walls. Thus, at Altamira, engravings on bone associated with Solutrean and Magdalenian flints enabled Alcalde del Rio and Breuil to date the engravings on the limestone walls. Hence, in grottos which have never been closed up and which have been frequented at different times from the Palæolithic to the present epoch one observes that the mural designs in the caverns are invariably accompanied by Upper Palæolithic implements with a similar style of decoration; and this is the case at Font-de-Gaume, Combarelles, Portel, Mas d'Azil, Castillo, Pasiega, and Hornos de la Peña. The bone engravings of the female red deer found at Altamira are identical in their artistic period with those found on the walls of the same grotto. The excavations at Castillo, where numerous shoulder-blades of the deer were found engraved in the same style as those of Altamira, prove that all these engravings and drawings are to be referred to ancient Magdalenian rather than to upper Solutrean times. The engravings upon the walls in the grotto of Hornos de la Peña, of Aurignacian times, are dated through the discovery at the base of the layer of Aurignacian flints of an engraved equine figure similar to the engravings at Altamira. A fourth method applies to those not infrequent cases when two or three designs are superposed one upon the other, from which it necessarily follows that the underlying designs must antedate those above. Through the application of these four methods Breuil has succeeded in dating all the steps in the advance of art from Aurignacian into Magdalenian times. ENGRAVING, PAINTING, AND SCULPTURE In the archaic drawings of the caverns of Pair-non-Pair, La Grèze, and La Mouthe most of the animal figures are somewhat heavily and deeply engraved; the proportions are not true; the head is usually too small, with a large, short body which is often lightly modelled, resting on thin extremities. Quadrupeds are frequently represented with but two legs, as in the case of the mammoth. That the powers of observation were only gradually trained is shown by the fact that details which in later drawings are well observed are here overlooked; the profile drawings of animals, with one fore leg and one hind leg represented, are quite like those of children.