Of the first class of works, it has been sufficiently demonstrated, that a small proportion were intended for works of defence; that another portion were sacred places, or in some way connected with religious or superstitious rites, while a third and much the larger number are entirely inexplicable in our present state of information. The tumuli are divided into three grand classes, which are broadly marked in the aggregate, though there are individual instances of an anomalous character. These are: 1st. Tumuli of sepulture, each containing a single skeleton enclosed in a rude, wooden coffin, or an envelope of bark or matting, and occurring in isolated or detached groups. 2d. Tumuli of sacrifice, containing symmetrical altars of stone or burnt clay, occurring within or in the immediate vicinity of enclosures, and always stratified. 3d. Places of observation, or mounds raised upon elevated or commanding positions. Within these monuments have been found implements and ornaments of silver, copper, lead, stone, ivory and pottery, fashioned into a thousand forms, and evincing a skill in art, to which the existing race of Indians, at the time of their discovery, could not approach. Marine shells, mica from the primitive regions, native copper from the shores of lake Superior, galena from the upper Mississippi, cetacean teeth, pearls and instruments of _obsidian_, show the extent of communication and intercourse had by the authors of these ancient works. Sculptures of animals, birds and reptiles have been found in great numbers and variety, exhibiting a skill which few could now surpass. Also, sculptures of the human head, disclosing most probably the character of the physiognomy, as well as the manner of adjusting the hair, the head dress and ornaments of the mound-builders. Careful admeasurements of the earth works which abound in the Ohio valley, have been made by the gentlemen alluded to, in which the interesting fact has been developed, that many of them are perfect circles and squares, and hence that the people by whom they were constructed had some means of determining angles and of constructing circles. In some of those earth-heaps, sufficient remains to show that when in a perfect state, they resembled the _teocallis_ or terraced edifices of Mexico and Yucatan, though they were composed wholly of wood and earth.