The investigation of this class of ancient works suggests many curious questions to which it is difficult to furnish any satisfactory answer. It seems probable that not only each successive stage in the use and reconstruction of the altar, but in the building of the superincumbent mound, had its own significance and accompanying rites. In one of the “Mound City” structures, after penetrating through four successive sand-strata, interposed at intervals of little more than a foot between layers of earth; and excavating altogether to a depth of nineteen feet: a smooth level floor of slightly burned clay was found, covered with a thin layer of sand, and on this a series of round plates of mica, ten inches or a foot in diameter, were regularly disposed, overlapping each other like the scales of a fish. The whole deposit was not uncovered, but sufficient was exposed to lead the observers to the conclusion that the entire layer of mica was arranged in the form of a crescent, the full dimensions of which must measure twenty feet from horn to horn, and five feet at its greatest breadth. In some mounds the accumulated carbonaceous matter, like that formed by the ashes of leaves or grass, might suggest the graceful offerings of the first-fruits of the earth. In others, the accumulation of hundreds of elaborately carved stone pipes on a single altar, is suggestive of some ancient peace- or war-pipe ceremonial, in which the peculiar American custom of tobacco-smoking had its special significance, and even perhaps its origin. In others again, we should perhaps trace in the deposition under the sacred mound of hundreds of spear and arrow-heads, copper axes, and other weapons of war, a ceremonial perpetuated in the rude Indian symbolism of burying the tomahawk or war-hatchet. But looking to the evidence which so clearly separates the sepulchral from the sacred mounds, it is scarcely possible to avoid the conclusion that on some of the altars of the Mound-Builders human sacrifices were made; and that within their sacred enclosures were practised rites not less hideous than those which characterised the worship which the ferocious Aztecs are affirmed to have regarded as most acceptable to their sanguinary gods. Among the Mexicans, if we are to believe the narratives of their Spanish conquerors, human sacrifices constituted the crowning rite of almost every festival. That great exaggeration is traceable in the narratives of the chronicles is admitted in part even by the enthusiastic historian of the conquest of Mexico; and the charming historical romance woven by Prescott, is perhaps even more open to question in its reproduction of the gross charges of cannibalism and wholesale butchery in the superstitious rites of the Mexicans: than in its gorgeous picturings of their architectural magnificence, their temples and palaces, sculptured fountains, floating gardens, and all the strange blending of Moorish luxury, with the refinements of European