[Footnote 28: "No manure was used," says Mr. Parkman, speaking of the Hurons, "but at intervals of from ten to twenty years, when the soil was exhausted and firewood distant, the village was abandoned and a new one built." _Jesuits in North America_, p. xxx.] [Sidenote: Middle status of barbarism.] Let us now observe some characteristics of this extremely interesting middle period. It began, we see, in the eastern hemisphere with the domestication of other animals than the dog, and in the western hemisphere with cultivation by irrigation and the use of adobe-brick and stone for building. It also possessed another feature which distinguished it from earlier periods, in the materials of which its tools were made. In the periods of savagery hatchets and spear-heads were made of rudely chipped stones. In the lower period of barbarism the chipping became more and more skilful until it gave place to polishing. In the middle period tools were greatly multiplied, improved polishing gave sharp and accurate points and edges, and at last metals began to be used as materials preferable to stone. In America the metal used was copper, and in some spots where it was very accessible there were instances of its use by tribes not in other respects above the lower status of barbarism,--as for example, the "mound-builders." In the Old World the metal used was the alloy of copper and tin familiarly known as bronze, and in its working it called for a higher degree of intelligence than copper. [Sidenote: Working of metals.] Toward the close of the middle period of barbarism the working of metals became the most important element of progress, and the period may be regarded as ending with the invention of the process of smelting iron ore. According to this principle of division, the inhabitants of the lake villages of ancient Switzerland, who kept horses and oxen, pigs and sheep, raised wheat and ground it into flour, and spun and wove linen garments, but knew nothing of iron, were in the middle status of barbarism. The same was true of the ancient Britons before they learned the use of iron from their neighbours in Gaul. In the New World the representatives of the middle status of barbarism were such peoples as the Zunis, the Aztecs, the Mayas, and the Peruvians. [Sidenote: Upper status of barbarism.] [Sidenote: Beginning of civilization.]