No estimate can be made of the time represented by the 65,000 feet of fossiliferous strata known to us and the same thickness of non-fossiliferous deposit which precedes them. There are no facts known upon which a calculation of the related lapse of time can be based. But most geologists would agree that whilst we have good ground for assigning half a million years to the formation of the Pleistocene strata, it is not an unreasonable supposition that the period required for the formation of the fossiliferous rocks which precede them in time, is not less and probably more than five hundred million years. [Illustration: FIG. 14.–Drawing (of the actual size of the original) of a flat carving in shoulder-bone of a horse's head, showing twisted rope-bridle and trappings. _a_ appears to represent a flat ornamented band of wood or skin connecting the muzzling rope _b_ with other pieces _c_ and _d_. This specimen is from the cave of St. Michel d'Arudy, and is of the Reindeer period. This, and others like it are in the same museum of St. Germain.] [Illustration: FIG. 15.–Drawing (of the actual size of the original) of a fully rounded carving in reindeer's antler of the head of a neighing horse. The head resembles that of the Mongolian horse. This is one of the most artistic of the cave-men's carvings yet discovered. It is of the Palæolithic age (early Reindeer period), probably not less than 50,000 years old. It was found in the cavern of Mas d'Azil, Ariège, France, and is now in the museum of St. Germain.] The pictures and carvings with which we are for the moment concerned all belong to the _later_ Pleistocene or Reindeer epoch. None have been found in the middle and earlier Pleistocene, though finely-chipped flints of several successive types are found in those earlier beds. So that it is clear that many successive ages of man had elapsed in Western Europe before these pictures–immensely ancient as they are–were executed. The men who made these works of art had ages of humanity, tradition, and culture (of a kind) behind them. Yet they were themselves tens of thousands of years earlier than the ancient Egyptians! [Illustration: FIG. 16.–Reindeer engraving on schist, small size (cavern of Laugerie basse).] [Illustration: FIG. 17.–Rhinoceros in red outline (2½ feet long), drawn on the wall of the cavern of Font de Gaume.]