The rock shelter at La Madeleine has given its name to the closing epoch of the Palaeolithic Age. The flint industry shows distinct decadence, but the working in bone and horn was at its zenith; indeed, so marked is the contrast between this and the preceding stage that Breuil is convinced that "the first Magdalenians were not evolved from the Solutrians; they were new-comers in our region[48]." The typical implements are barbed harpoons in reindeer antler (later that of the stag), often decorated with engravings. Sculpture and engravings of animals in life-like attitudes are among the most remarkable records of the age, and the polychrome pictures in the caves of Altamira, "the Sistine chapel of Quaternary Art," are the admiration of the world[49]. In the cave of Mas-d'Azil, between the Magdalenian and Neolithic deposits occurs a stratum, termed Azilian, which, to some extent, bridges over the obscure transition between the Palaeolithic and Neolithic Ages. The reindeer has disappeared, and its place is taken by the stag. The realistic art of the Magdalenians is succeeded by a more geometric style. In flint working a return is made to Aurignacian methods, and a particular development of pygmy flints has received the name _Tardenoisian_[50]. The characteristic implement is still the harpoon, but it differs in shape from the Magdalenian implement, owing to the different structure of the material. Painted pebbles, marked with red and black lines, in some cases suggesting a script, have given rise to much controversy. Their meaning at present remains obscure[51]. The question of prehistoric chronology is a difficult one, and the more cautious authorities do not commit themselves to dates. Of late years, however, such researches as those of A. Penck and E. Brueckner in the Alps[52] and of Baron de Geer and W. C. Brogger in Sweden[53], have provided a sound basis for calculations. Penck recognises four periods of glaciation during the pleistocene period, which he has named after typical areas, the Guenz, Mindel, Riss and Wuerm. He dates the Wuerm maximum at between 30,000 and 50,000 years ago and estimates the duration of the Riss-Wuerm interglacial period at about 100,000 years. According to his calculations the Chellean industry occurs in the Mindel-Riss, or even in the Guenz-Mindel interval, but it is more commonly placed in the mild phase intervening before the last (Wuerm) glaciation, this latter corresponding with the cold Mousterian stage. At least four subsequent oscillations of climate have been recognised by Penck, the Achen, Buehl, Gschnitz and Daun, and the correspondence of these with palaeolithic culture stages may be seen in the following table[54]. Penck and Brueckner Obermaier and others Rutot