They are most abundant where the agricultural capabilities of the country are greatest, and we find them associated with areas of special fertility in such a way as to prove that they had stripped the forest from these areas, and chiefly derived their subsistence from their cultivation. Hence we learn that they were a sedentary and agricultural people. Yet their structures are for the most part earthworks—walls for defense, or to form inclosures, sepulchral mounds, etc.; and while we find what seem to be raised foundations of extensive buildings, those buildings have disappeared, and we must hence conclude that they were for the most part structures of wood.
The mound-builders were ignorant of the use of iron, and probably possessed no other metals than copper, which they mined extensively, but never smelted; for we find their implements composed of the native metal, often with specks of silver, thus betraying its source on Lake Superior, and only hammered into shape. From this copper they made battle-axes, daggers, knives, awls, and ornaments; but most of their tools and weapons were of stone, and many of them were laboriously and tastefully wrought.
They have left no evidence that they had a knowledge of masonry—an art in which the inhabitants of the table-lands so much excelled.
This is the more remarkable, as stone easily quarried abounds in the vicinity of their works, and some of the great structures of our Western table-lands, whose builders apparently had not the use of metals, show what good work could be done without metallic tools.
I have said that the mound-builders made use of but a single metal—copper—and yet they were industrious and enterprising miners. Their copper mines on Lake Superior have been often and fully described. They must have been worked for generations, since the ancient excavations exceed in magnitude all the work of the white man in that region; but the methods which they used were exceedingly rude and simple.
They had no knowledge of metallurgy, and the Lake Superior copper was only available for their purpose because it occurs in the metallic state. They excavated the rock by the use of fire, stone hammers, and wooden shovels.
They never penetrated the earth to a greater depth than sixty to eighty feet, and for ladders they used the trunks of trees from which the branches projected at frequent intervals, and these were cut off to form steps. Since no considerable structures belonging to this people have been found near the Lake Superior mines, it seems probable that their mining operations were carried on only in summer, and by parties who, migrating from the lower country in the spring, returned in autumn.
