[Illustration: II. Map of a section of twelve miles of the Scioto Valley with its ancient monuments.]
Further to the southward, in the region watered by the Ohio and its tributaries, we find ancient works of greater magnitude and more manifest design. Among them are a few animal-shaped structures; but they seem to have been erected on different principles and for a different purpose from those just noticed. Here we find numberless mounds, most of them conical but many pyramidal in form, and often of great dimensions. The pyramidal structures are always truncated, sometimes terraced, and generally have graded ascents to their summits. They bear a close resemblance to the Teocallis of Mexico; and the known uses of the latter are suggestive of the probable purposes to which they were applied. Accompanying these, and in some instances sustaining an intimate relation to them, are numerous enclosures of earth and stone, frequently of vast size, and often of regular outline. These are by far the most imposing class of our aboriginal remains, and impress us most sensibly with the numbers and power of the people who built them. The purposes of many of these are quite obvious; and investigation has served to settle, pretty clearly, the character of most of the other works occurring in connection with them.
Proceeding still further southwards, we find, in the States bordering on the Gulf of Mexico, the mounds increasing in size and regularity of form, if not in numbers. Conical mounds become comparatively rare, and the Teocalli-shaped structures become larger and more numerous, and assume certain dependencies in respect to each other, not before observed. The enclosures, on the other hand, diminish in size and numbers; and lose many of the characteristic features of those of a higher latitude, though still sustaining towards them a strong general resemblance. Here, for the first time, we find traces of bricks in the mounds and in the walls of enclosures.
The peculiarities of these several divisions will be more particularly pointed out in the progress of this work; when the points of resemblance and difference will become more apparent. The succeeding observations relate more especially to the remains included in the central geographical section above indicated, where the investigations recorded in this volume were principally carried on, and which, in the extent, variety, and interesting nature of its ancient monuments, affords by far the richest and most important field for archæological research and inquiry.