The ancient art-products of each of these areas have well-marked peculiarities, with which one who would master the subject must acquaint himself; but for our present purpose it will be sufficient merely to call attention to this general fact, in order that the descriptions we are about to give may not be indiscriminately applied.
Other division of the Neolithic Period in the area of the United States, especially in its central portions—a division to which some archeologists attach great importance—is that of the "upper" and "lower," or "surface" and "mound," series of relics. This is based on the fact that much the larger portion of what we have above defined as "the area of the Mississippi Valley" was, when first explored by the whites, destitute of inhabitants, and yet by the presence of lofty mounds of earth and stones, massive earthworks, extensive embankments and garden-plots overgrown with heavy timber, showed beyond question that at some long anterior time it had been the busy scene of dense popula tions. (See Vol. I. pp. 215, 216, 224, 225, 5/• 32, 37-39.) This subdivision is probably of less importance than many have main tained. There are many strong reasons for believing that the builders
of the earthworks of the Ohio Valley were a people of the same stage of culture as, and probably ancestrally akin to, the tribes met by the early white explorers in the Gulf States. These at one time appear to have extended their agriculture and their methods of construction almost up to the Great Lakes; but at a period which we may fix at a few centuries before the advent of the whites the hardy and warlike northern tribes attacked the more peaceful southern agriculturists, destroyed their towns, and drove the inhabitants far to the south. We shall, therefore, not lay any especial stress on this distinction. The Mound-builders were in the higher, neolithic stage of development, but were not superior to several of the tribes with whom we are familiar in the Gulf States.
Pursuing the general plan which investigates the art-products of man with reference to the material in which lie worked, we shall study the Archaeology of this and the other areas of the continent as it is represented by articles in stone, bone, shell, clay, and metal.