The Mound Builders made sun-dried brick mixed with rushes, as the Egyptians made sun-dried bricks mixed with straw; they worked in copper, silver, lead, and there are evidences, as we shall see, that they wrought even in iron.

Copper implements are very numerous in the mounds.  Copper axes, spear-heads, hollow buttons, bosses for ornaments, bracelets, rings, etc., are found in very many of them strikingly similar to those of the Bronze Age in Europe.  In one in Butler County, Ohio, was found a copper fillet around the head of a skeleton, with strange devices marked upon it.

Silver ornaments have also been found, but not in such great numbers.  They seem to have attached a high value to silver, and it is often found in thin sheets, no thicker than paper, wrapped over copper or stone ornaments so neatly as almost to escape detection.  The great esteem in which they held a metal so intrinsically valueless as silver, is another evidence that they must have drawn their superstitions from the same source as the European nations.

Copper is also often found in this manner plated over stone pipes, presenting an unbroken metallic lustre, the overlapping edges so well polished as to be scarcely discoverable.  Beads and stars made of shells have sometimes been found doubly plated, first with copper then with silver.

The Mound Builders also understood the art of casting metals, or they held intercourse with some race who did; a copper axe it “cast” has been found in the State of New York. (See Lubbock’s “Prehistoric Times,” p. 254, note.) Professor Foster ("Prehistoric Races,” p. 259) also proves that the ancient people of the Mississippi Valley possessed this art, and he gives us representations of various articles plainly showing the marks of the mould upon them.

A rude article in the shape of an axe, composed of pure lead, weighing about half a pound, was found in sinking a well within the trench of the ancient works at Circleville.  There can be no doubt it was the production of the Mound Builders, as galena has often been found on the altars in the mounds.

It has been generally thought, by Mr. Squier and others, that there were no evidences that the Mound Builders were acquainted with the use of iron, or that their plating was more than a simple overlaying of one metal on another, or on some foreign substance.

Some years since, however, a mound was opened at Marietta, Ohio, which seems to have refuted these opinions.  Dr. S. P. Hildreth, in a letter to the American Antiquarian Society, thus speaks of it: