The hair of the American Indians is always black, long, coarse, and uncurled. With rare exceptions they carefully eradicate their scanty beard. Their forehead is generally low, their black and deep-seated eyes have their upper angles turned upwards, and their cheek-bones are broad and high. While they thus in some of their features resemble the Mongol type, they widely differ from it by the form of their nose, which is as prominent as in the Caucasian race. The mouth is large, the lips broad, but not thick as those of the Negro; the chin short and round, the jaws remarkably strong and broad. The expression of the eye is in some tribes mild and serene, in others it shows a forbidding mixture of melancholy and ferocity. There is generally a remarkable rigidity in the features of the American, very different from that lively play in a European countenance, which often reflects as a mirror every emotion of the mind. Some tribes are of small stature, others athletic; the limbs are generally well-turned; the feet small; the body of just proportions. The beardless countenance and smooth skin seem to indicate a defect of vigour which does not exist in reality. In those parts of the continent where hardly any labour is requisite to procure subsistence, and the powers of the body and mind are not called forth, indolence indeed produces its usual effects, weakness and languor; but wherever the aboriginal American is accustomed to toil, he is found capable of performing such tasks as equal any effort of the natives either of Africa or of Europe. In many of the silver mines of Mexico, where the ore is conveyed to the surface by human labour, the native Indians will climb steep ladders with 240 to 380 pounds, and perform this hard work for six hours consecutively. Their muscular strength seemed truly astonishing to Humboldt, who, though having no weight but his own to carry, felt himself utterly exhausted after ascending from a deep mine.[9] In propelling a boat against a rapid stream, or in supporting the fatigues of a long march, the Indian evinces similar powers of endurance and exertion, which prove him to be not inferior in this respect to the other races of man.