Science accepted Mortillet’s system of orderly cultures and the theory of successive core and flake industries, and for fifty years tried to apply it to new discoveries both in Europe and elsewhere. Though the system has had to be modified in parts, and in parts abandoned, its terms are still used, and used in a way that is confusing because the terms are no longer exact. In Africa the various types of tools resemble only approximately those of Europe, and they do not seem to correspond in time. The hand ax may have spread from Spain into almost all Africa, or, more probably, from Africa into Spain, as well as southern India, but there are plenty of flaked tools, too, in these regions. Central and northern Asia seem to be devoted to the flake, and to eschew the hand ax in favor of a kind of chopping tool made out of a core. Asia, like Africa, has tools made out of large, smooth pebbles. Dating Early Man in Europe One good thing can be said for Mortillet’s modified sequence of Abbevillian, Acheulean, Mousterian, Aurignacian, Solutrean, and Magdalenian. It may not be complete enough, and it may not apply too well to the world outside Europe; but it is chronologically sound locally. It is a succession of cultures along a time scale. If an archaeologist finds two or more varieties of paleolithic tools in a new site, he finds, for example, Acheulean beneath Mousterian, or Mousterian beneath Aurignacian. Similarly, when he comes upon Abbevillian and Acheulean in separate terraces of the same river, he always finds the Abbevillian in a higher terrace than the Acheulean, and, as we have explained on pages 51 and 52, the higher terrace is always the older. Dating these cultures in terms of our years is another matter. The first step is fairly simple. If the tools are found with the fossils of a warmth-loving animal like the hippopotamus, they belong to an interglacial period; if they are found with the fossils of an animal like the hairy mammoth, which could survive a harsh climate, they belong to a glacial time. The species of animal may determine which glacial or which interglacial. If the tools are found in the gravel of a certain river terrace, then they belong to the geological period when the material of the terrace was being laid down. The terraces often contain fossils, and this may cross-date the terrace materials with cave deposits. But scientists are often faced with the problem of picking the right glacial or interglacial period on scanty evidence, and the still more difficult problem of setting the period in the terms of our years. There is room here for much disagreement. Glaciologists do not agree as to the age or the length of the various glacials and interglacials (see illustration, page 55). Some prehistorians accept and use the dates of one glacialist; some choose another’s. They do not all concur as to which culture came in which glacial period. True Tools—Deceptive Skulls