This indicates their locality and distribution. It has also indicated their nature and character. Oftener earthworks than buildings of stone, they are generally (but not exclusively) either raised mounds or embankments forming enclosures,--mounds in some cases 70 feet in height, and 1000 in circumference at the base, and embankments (with ditches corresponding) enclosing spaces of 300 acres. Such are some of the greatest measurements. In form both the mound and embankment are very varied. The enclosure may be a square, a circle, a parallelogram, an ellipse, a polygon, or a wholly irregular outline, following the inequalities of the soil or the configuration of the country in which it occurs. The ditch may be either exterior or interior to it; the entrance simple or complex. Sometimes the square and circle are combined; so that a round inclosure leads into a quadrangle, or _vice versâ_. Sometimes a quadrangle is enclosed with a square. [Illustration] The mounds are sometimes simple cones; sometimes (an important difference) truncated pyramids; often simple slopes; often terraced. More remarkable, however, than any others, is "a succession of remains, entirely singular in their forms, and presenting but slight analogy to any others of which we have an account, in any portion of the globe. The larger proportion of these are structures of earth, bearing the forms of beasts, birds, reptiles, and even of men; they are frequently of gigantic dimensions, constituting huge _basso-relievos_ upon the face of the country. They are very numerous, and in most cases occur in long and apparently dependent ranges. In connection with them are found many conical mounds and occasional short lines of embankment, in rare instances forming enclosures."[137] The reader anticipates the object for which these works were undertaken--the purposes of war and the purposes of religion. This is the most general way of stating it; those for the latter purposes falling in the divisions of sepulchral and sacrificial. [Illustration] Besides the usual human remains which are found in the sepulchral mounds, works in stone, earthenware, and metal are frequent; relics which, taken along with the vast and numerous works which contain them, give us the elements of the ante-historical civilization of the northern section of the North American Indians. The prevalence of works of a certain type varies with the area. The animal bas-reliefs are chiefly characteristic of Wisconsin, the truncated pyramids of the southern States, the simple mound and enclosure of Ohio, and the midland parts. It should now be added, that where a square is attempted, it is truly rectangular, and that the circles are generally perfect; also that, in several cases, either the sides or the entrances accurately coincide with the east, west, north, and south points of the compass.