The evolution of the Pre-Chellean into the Chellean and finally into the Lower Acheulean palæoliths certainly occupied a very long period of time if we assign it merely the 50,000 or 60,000 years allotted to the Third Interglacial; but even this allotment seems far too long when we observe the relatively limited depth of the river deposits in which these flint cultures succeed each other. For we cannot fail to be impressed by the regular and very close and unbroken succession of the geologic layers containing the Chellean and Acheulean artifacts. (See Fig. 55.) None the less it follows that a long lapse of time must be allowed for each culture period, and for the advance in technique.(3) It is this wide distribution that has enabled the de Mortillets (father and son), Capitan, Rivière, Reboux, Daleau, Peyrony, Obermaier, Commont, Schmidt, and others to establish in various parts of Europe the main stages of the industrial evolution of the Old Stone Age, or Lower Palæolithic. SUBDIVISIONS OF THE LOWER PALÆOLITHIC CULTURES(4)[T] MOUSTERIAN. Late industry of the Neanderthal races. Extensive use of the 'flake.' _Late Mousterian._ La Quina scrapers, small 'coups de poing,' and bone anvils, closing with the Abri Audit culture. _Middle Mousterian._ Culmination of the Mousterian 'point' finely flaked and chipped on one side, the best examples approaching the Solutrean perfection of technique. _Early Mousterian._ Heart-shaped 'coups de poing' and Mousterian flake 'points' and flake scrapers. ACHEULEAN. Early industry of the Neanderthal races. Extensive use of the nodular core. _Late Acheulean._ Miniature 'lance points' of La Micoque type, triangular 'coups de poing,' and flint flakes of Levallois type. _Middle Acheulean._ Pointed oval 'coups de poing,' much lighter than the Chellean types, and small implements similar to the Chellean but much improved in workmanship. _Early Acheulean._ Broad oval 'coups de poing' much more symmetrical than the Chellean but still rather heavy. Small types. CHELLEAN. _Late Chellean._ Long pointed 'coups de poing,' in most cases flaked on both sides, with little of the crust of the nodule adhering and the edges still unsymmetrical. First appearance of the oval 'coups de poing.' _Early Chellean._ First appearance of 'coups de poing' of almond shape. Small implements, including scrapers, planes, and borers. All implements unsymmetrical and with uneven edges. PRE-CHELLEAN. Probable industry of the Piltdown and of the (Pre-Neanderthaloid) Heidelberg races. Use of chance and accidental forms. Forms partly accidental; retouch limited to the few strokes necessary to give a point or edge to the tool, or to allow a firm grasp (protective retouch). Prototypes of 'coup de poing' formed of flint nodules with crust only partially removed.