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 OF THE MISSISSIPPI VALLEY. 11

fifty acres, are common ; while enclosures of one hundred or two, hundred acres area are far from infrequent. Occa- sional works are found, embracing not less than five or six hundred acres.* The magnitude of the area enclosed is not, however, always an index of the amount of the labor expended in the construction of these works, or of the length of the embankment raised. A fortified hill, in High- land county, Ohio, has one mile and five-eighths of heavy embankment; yet it encloses an area of only about forty acres. A similar work, on the Little Miami river, in Warren county, Ohio, has upwards of four miles of embankment yet encloses but little upwards of one hundred acres. The group of works at the mouth of the Scioto river has an aggregate of at least twenty miles of embankment; yet the amount of land em- braced within the walls does not exceed two hundred acres.

The mounds are of every conceivable dimension, from those of but a few feet in height and a few yards in diame- ter, to those which, like the celebrated one at the mouth of Grave Creek, in Virginia, measure one thousand feet in circumference by seventy feet in height; or, like the trun- cated pyramid at Cahokia, in Illinois, rise to the altitude of nearly one hundred feet, and measure half a mile in cir- cumference at the base, with a level summit of several acres area. Their usual dimensions are, however, consid- erably less than in the examples here given. The larger number range from six to thirty feet in height, by forty to one hundred feet base.

These constructions are composed of earth or stone, taken up on the spot, or brought from localities more or less remote; though a combination of these materials, in the same work, is by no means rare. In the absence of ditches interior or exterior to the embankments, pits or dug holes, from which the earth for their construction was taken, are generally visible near by. These are sometimes very

“Lewis and Clarke describe one on the Missouri river which they esti- mated to contain six hundred acres.