water, Mr. Knapp
discovered a detached mass of copper weighing nearly six tons. It lay
upon a cob-work of round logs or skids six or eight inches in diameter,
the ends of which showed plainly the marks of a small axe or cutting
tool about two and a half inches wide. They soon shriveled and decayed
when exposed to the air. The mass of copper had been raised several
feet, along the foot of the lode, on timbers, by means of wedges." At
this place was found a stone maul weighing thirty-six pounds, and also a
copper maul or sledge weighing twenty-five pounds. Old trees showing 395
rings of annual growth stood in the debris, and "the fallen and decayed
trunks of trees of a former generation were seen lying across the pits."
Figure 19 (opposite) presents a section of this mining shaft of the
Mound-Builders: _a_ shows the mass of copper; _b_ the bottom of the
shaft; _c_ the earth and debris which had been thrown out. The dark
spots are masses of copper.

The modern mining works are mostly confined to that part of the copper
region known as Keweenaw Point. This is a projection of land extending
into Lake Superior, and described as having the shape of an immense
horn. It is about eighty miles in length, and, at the place where it
joins the main land, about forty-five miles in width. All through this
district, wherever 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 works is larger than
that which includes the modern mines, for they are known to exist in the
dense forests of other districts, to which the modern mining has not
yet been extended.

[Illustration: Fig. 19.--Ancient Mining Shaft.]

One remarkable mining excavation of the Mound-Builders was found near
the Waterbury mine. Here, in the face of a vertical bluff, was
discovered "an ancient, artificial, cavern-like recess, twenty-five feet
in horizontal length, fifteen feet high, and twelve feet deep. In front
of it is a pile of excavated rock on which are standing, in full size,
the forest trees common to this region." Some of the blocks of stone
removed from this recess would weigh two or three tons, and must have
required levers to get them out. Beneath the surface rubbish were the
remains of a gutter or trough made of cedar, placed there to carry off
water from the mine. At the bottom of the excavation a piece of white
cedar timber was found on