62 WISCONSIN ACADEMY SCIENCES, AETS, AND LETTERS. 



phyr}^ is a very hard stone and could only have been worked with 

 tools made of the hardest material. Obsidean is of volcanic origin 

 and much used by the Peruvians and Mexicans for arms and cutting 

 instruments. It is found in its natural state no nearer the Missis- 

 sippi Valley than the Mexican mountains of Cerro Gordo. The 

 art of spinning and weaving was known to them as evidenced by 

 the cloth found in the mounds. 



Before any evidence of ancient mining was discovered in the 

 Lake Superior copper region, pieces of copper with blotches of sil- 

 ver appearing to be welded to it but not alloyed with it, had been 

 dug from mounds. As this condition is peculiar to the Lake Su- 

 perior copper, it was supposed that the Mound-Builders were ac- 

 quainted with the art of mining. This was proven to be so in 

 1848, The moderii mining works are mostly confined to that part 

 of the copper region known as Keeweenaw Point. This is a pro- 

 jection of land extending into Lake Superior. It is about eighty 

 miles in length, and at the point where it joins the main-land, 

 about forty-five miles in width. All through this district, where- 

 ever modern miners have worked, remains of ancient mining works 

 are abundant; and they are extensive on the adjacent island, known 

 as Isle Royale. 



The area covered by the ancient vv^orks is greater than that which 

 includes the modern mines, as they are known to exist in the dense 

 forests of other district where modern mining.has not as yet extend- 

 ed. Their mining was chiefly surface work ; that is, they worked the 

 surface of the veins in open pits and trenches. The mounds differ 

 greatly in size. At Grrave Creek, West Virginia, there is one TO 

 feet high and 1,000 feet in circumference. One at Miamisburg, 

 Ohio, 68 feet high and 852 feet in circumference. Another at Ca- 

 hokia, Illinois, is TOO feet long, 500 wide, and 90 feet high. Thej^ 

 range generally from 5 to 30 feet in height. It is supposed that 

 the lower mounds were used for the same purposes as the mounds, 

 in Mexico and Central America, for the foundation of their princi- 

 ple buildings. But these buildings, having been built of wood, soon 

 perished, leaving no trace behind them save this earthen base. The 

 high mounds are pyramidal in shape and have level summits of 

 considerable extent, which were reached by stairways on the out- 

 side as those at Miamisburg, Ohio, and Grave Creek, West Virginia, 

 which resemble the great mounds at Chichen, Itza, and Mayapan^ 



