But, although we may be unable to estimate the minimum of time required for the changes in physical geography above alluded to, we cannot fail to perceive that the duration of the period must have been very protracted, and that other ages of comparative inaction may have followed, separating the Pleistocene from the historical periods, and constituting an interval no less indefinite in its duration. CHAPTER 5. -- PLEISTOCENE PERIOD--FOSSIL HUMAN SKULLS OF THE NEANDERTHAL AND ENGIS CAVES. Human Skeleton found in Cave near Dusseldorf. Its geological Position and probable Age. Its abnormal and ape-like Characters. Fossil Human Skull of the Engis Cave near Liege. Professor Huxley's Description of these Skulls. Comparison of each, with extreme Varieties of the native Australian Race. Range of Capacity in the Human and Simian Brains. Skull from Borreby in Denmark. Conclusions of Professor Huxley. Bearing of the peculiar Characters of the Neanderthal Skull on the Hypothesis of Transmutation. FOSSIL HUMAN SKELETON OF THE NEANDERTHAL CAVE NEAR DUSSELDORF. Before I speak more particularly of the opinions which anatomists have expressed respecting the osteological characters of the human skull from Engis, near Liege, mentioned in the last chapter and described by Dr. Schmerling, it will be desirable to say something of the geological position of another skull, or rather skeleton, which, on account of its peculiar conformation, has excited no small sensation in the last few years. I allude to the skull found in 1857 in a cave situated in that part of the valley of the Dussel, near Dusseldorf, which is called the Neanderthal. The spot is a deep and narrow ravine about 70 English miles north-east of the region of the Liege caverns treated of in the last chapter, and close to the village and railway station of Hochdal between Dusseldorf and Elberfeld. The cave occurs in the precipitous southern or left side of the winding ravine, about sixty feet above the stream, and a hundred feet below the top of the cliff. The accompanying section (Figure 1.) will give the reader an idea of its position. [Illustration: Figure 1] When Dr. Fuhlrott of Elberfeld first examined the cave, he found it to be high enough to allow a man to enter. The width was 7 or 8 feet, and the length or depth 15. I visited the spot in 1860, in company with Dr. Fuhlrott, who had the kindness to come expressly from Elberfeld to be my guide, and who brought with him the original fossil skull, and a cast of the same, which he presented to me. In the interval of three years, between 1857 and 1860, the ledge of rock, f, on which the cave opened, and which was originally 20 feet wide, had been almost entirely quarried away, and, at the rate at which the work of dilapidation was proceeding, its complete destruction seemed near at hand. (FIGURE 1. SECTION OF THE NEANDERTHAL CAVE NEAR DUSSELDORF.