Post-glacial {Daun } Azilian Proto-Neolithic} with {Gschnitz} Azilian } oscillations {Buehl } Magdalenian } Neolithic {Achen } Magdalenian Solutrian and } } Aurignacian } IV. Wuerm. 4th Glacial } Mousterian Lower Lower Mousterian Magdalenian and Acheulean Riss-Wuerm. 3rd Solutrian and Chellean Upper Interglacial Aurignacian Mousterian Warm Mousterian III. Riss. 3rd Glacial Cold Mousterian Lower Acheulean Chellean Mindel-Riss. 2nd Acheulean Mauer jaw Strepyan Interglacial Chellean Pre-Palaeolithic Mesvinian Mafflian II. Mindel. 2nd Glacial } } } } Guenz-Mindel. 1st } No artefacts } No artefacts Interglacial } } } } I. Guenz. 1st Glacial } } James Geikie[55], under the heading, "Reliable and Unreliable estimates of geological time," points out that the absolute duration of the Pleistocene cannot be determined, but such investigations as those of Penck "enable us to form some conception of the time involved." He accepts as a rough approximation Penck's opinion that "the Glacial period with all its climatic changes may have extended over half a million years, and as the Chellean stage dates back to at least the middle of the period, this would give somewhere between 250,000 and 500,000 years for the antiquity of man in Europe. But if, as recent discoveries would seem to indicate, man was an occupant of our Continent during the First Interglacial epoch, if not in still earlier times, we may be compelled greatly to increase our estimate of his antiquity" (p. 303). W. J. Sollas, on the other hand, is content with a far more contracted measure. Basing his calculations mainly on the investigations of de Geer, he concludes that the interval that separates our time from the beginning of the end of the last glacial episode is 17,000 years. He places the Azilian age at 5500 B.C., the middle of the Magdalenian age somewhere about 8000 B.C., Mousterian 15,000 B.C., and the close of the Chellean 25,000 B.C.[56]