In the details of their works, and in manufactured articles taken from the mounds, there is evidence of considerable civilization. For instance, it has been ascer

tained that the circular inclosures are perfect circles, and the square inclosures perfect squares. They were constructed with a geometrical precision which implies a kind of knowledge in the builders that may be called scientific. Figures 13, 14, 15, 16 show some of the more

Fig. 16.-Rectangular Work, Randolph County, Indiana.

important works of the Mound-Builders, chiefly in Ohio. Relics of art have been dug from some of the mounds, consisting of a considerable variety of ornaments and implements, made of copper, silver, obsidian, porphyry, and greenstone, finely wrought. There are axes, single and double; adzes, chisels, drills or gravers, lance-heads, knives, bracelets, pendants, beads, and the like, made of copper. There are articles of pottery, elegantly designed and finished; ornaments made of silver, bone, mica from the Alleghanies, and shells from the Gulf of Mexico.

The articles made of stone show fine workmanship; some of them are elaborately carved. Tools of some