The singular custom of perforating the skull after death (and possibly during life) is shown to have been in vogue by the discovery of a number of crania at the River Rouge Mound in Michigan with artificial apertures. No light as yet has been thrown upon the significance of this strange practice.[271] The nearest approach to the natural condition and characteristic physiognomy of the pre-historic inhabitants of this continent, is observable in the Peruvian mummies collected in latitude 18° 30´ S., on the shore of the Bay of Chacota, near Arica, by Mr. Blake, and transferred by him to Boston. Many others have since been exhumed, and though embalmed and buried in a climate which preserves the brightest colors of the garments with which they were enshrouded, still the shrivelled condition of the corpses furnishes us the assurance that their type of features can never be truly recovered from nature. Dr. Morton has figured the head of one of these mummies in Plate I of the _Crania Americana_, from which the physiognomy may be partially restored by the aid of a vivid imagination. Notwithstanding the temptation which presents itself, and one which has been sufficiently indulged already, it would certainly be idle to speculate as to what that type might have been. However, one feature of the Peruvian mummies has been preserved true to life, and is of the greatest value in determining ethnic relations. The silicious sand and marl of the plain southward of Arica, where the most remarkable cemeteries are situated, is slightly impregnated with common salt as well as nitrate and sulphate of soda. These conditions, together with the dry atmosphere rivalling that of Egypt, and in which fleshy matter dries without putrefaction, the human hair has been perfectly preserved, and comes to us as one of the best evidences of the diversity of the American races yet produced. In general it is a lightish brown, and of a fineness of texture which equals that of the Anglo-Saxon race.[272] Straight, coarse, black hair is universally characteristic of the Red Indians, and is known to be one of the last marks of race to disappear in intermarriage with Europeans. The ancient Peruvians appear, from numerous examples of hair found in their tombs, to have been an auburn-haired race. Garcilasso, who had an opportunity of seeing the body of the king Viracocha, describes the hair of that monarch as snow-white.[273] Haywood has described the discovery at the beginning of this century of three mummies in a cave on the south side of the Cumberland River, near the dividing line of Smith and Wilson Counties in Tennessee. They were buried in baskets, as Humboldt has described some of the Peruvians to bury, and the color of their skin was said to be fair and white, and their hair auburn and of a fine texture.[274] The same author refers to several instances of the discovery of mummies in the limestone and saltpetre caves of Tennessee with light yellowish hair.[275] Prof.