The geologic age of the bones referred to is a matter of first importance. The remains of _Pithecanthropus_ lay in a deposit about one meter in thickness, consisting of loose, coarse, tufaceous sandstones, below this a stratum of hard, blue-gray clay, and under that marine breccia. Above the _Pithecanthropus_ layer were the 'Kendeng' strata, a many-layered tufaceous sandstone, about 15 meters in thickness. This geologic series was considered by Dubois and others to be of late Tertiary or Pliocene age; _Pithecanthropus_ accordingly became known as the long-awaited 'Pliocene ape-man.' Subsequent researches by expert geologists have tended to refer the age to the early Pleistocene.(17) According to Elbert(18) the Kendeng strata overlying the _Pithecanthropus_ layer correspond to an early pluvial period of low temperature and, in point of time, to the Ice Age of Europe. For even in Java one can distinguish three divisions of the Pleistocene period, including the first period of low temperature to which the _Pithecanthropus_ layer is referred. [Illustration: FIG. 33. Section corresponding to line _A-B_ in Fig. 32, showing the river-drift gravels and sands at the point where the skull-top of _Pithecanthropus_ was found. Drawn by C. A. Reeds. Recent 7 River wash, blue-black clay. { 6 Light-colored sandstone, like tuff. { 5 Gray tuff with balls of clay, fresh-water shells. { 4 White streaked sandstone resembling tufa. Pleistocene { 3 Blue-black clay with plant remains. { 2 Bone-bearing stratum. _Pithecanthropus._ { 1 Lahar conglomerate.] The fossil mammals contained in the _Pithecanthropus_ layer have also been thoroughly studied,(19) and they tend to confirm the original reference to the uppermost Pliocene. They yield a very rich fauna similar to that of the Siwalik hills of India, including the porcupine, pangolin, several felines, the hyæna, and the otter. Among the primates beside _Pithecanthropus_ there is a macaque. Among the larger ungulates are two species of rhinoceros related to existing Indian forms, the tapir, the boar, the hippopotamus, the axis and rusa deer, the Indian buffalo, and wild cattle. It is noteworthy that three species of late Pliocene elephants, all known as _Stegodon_, and especially the species _Stegodon ganeza_, occur, as well as _Elephas hysudricus_, a species related to _E. antiquus_, or the straight-tusked elephant, which entered Europe in early Pleistocene times. Fossils of the same animals are found in the foot-hills of the Himalayas of India, about 2,500 miles distant to the northwest. The India deposits are considered of uppermost Pliocene age,(20) for this is the closing life period of the upper Siwaliks of India.