We now have to speak of those enclosures which are divided by American archæologists into the classes of _defensive_ and _sacred_. This distinction is, however, based on very uncertain data, and it is probable that a large portion of the so-called _sacred_ enclosures were in the first place constructed for a simply _defensive_ purpose. They were, in general, composed of a wall made of stones, and an internal or external ditch. They often assumed the form of a parallelogram, and even of a perfect square or circle, from which it has been inferred that the ancient Indians must have possessed an unit of measurement, and some means of determining angles. These walls sometimes embraced a considerable area, and not unfrequently inside the principal enclosure there were other smaller enclosures, flanked with defensive mounds performing the service of bastions. In some cases enclosures of different shapes are grouped side by side, either joined by avenues or entirely independent of one another. The most important of these groups is that at Newark, in the Valley of Scioto; it covers an area of 4 square miles, and is composed of an octagon, a square, and two large circles. The external wall of one of these circles is even at the present day 50 feet in width at the base, and 13 feet high; there are several doorways in it, near which the height of the wall is increased about 3 feet. Inside there is a ditch 6 feet in depth, and 13 feet in the vicinity of the doors, its width being about 40 feet. The whole enclosure is now covered by gigantic trees, perhaps 500 or 600 years old--a fact which points to a considerable antiquity for the date of its construction. When we reflect on the almost countless multitude, and the magnificent proportions of the monuments we have just described, we are compelled to recognise the fact that the American valleys must at some early date have been much more densely populated than at the time when Europeans first made their way thither. These peoples must have formed considerable communities, and have attained to a somewhat high state of civilisation--at all events a state very superior to that which is at present the attribute of the Indian tribes. Tribes which were compelled to seek in hunting their means of every-day existence, could never have succeeded in raising constructions of this kind. They must therefore necessarily have found other resources in agricultural pursuits. This inference is moreover confirmed by facts. In several localities in the United States the ground is covered with small elevations known under the name of _Indian corn-hills_; they take their rise from the fact that the maize, having been planted every year in the same spot, has ultimately, after a long course of time, formed rising grounds. The traces of ancient corn-patches have also been discovered symmetrically arranged in regular beds and parallel rows.