o two tenths of an inch. By placing the eye at
the diminished end, the extraneous light is shut from the pupil, and
distant objects are more clearly discerned."

He points out that the carving and workmanship generally are very
superior to Indian pipe carvings, and adds, if this article was a work
of the Mound-Builders "intended for a telescopic tube, it is a most
interesting relic." An ancient Peruvian relic, found a few years since,
shows the figure of a man wrought in silver, in the act of studying the
heavens through such a tube. Similar tubes have been found among relics
of the Mound-Builders in Ohio and elsewhere. In Mexico, Captain Dupaix
saw sculptured on a peculiar stone structure the figure of a man making
use of one. Astronomical devices were sculptured below the figure. This
structure he supposed to have been used for observation of the stars.
His account of it will be given in the chapter on Mexican and Central
American ruins.

The Mound-Builders used large quantities of copper such as that taken
from the copper beds on Lake Superior, where the extensive mines yield
copper, not in the ore, but as pure metal. It exists in those beds in
immense masses, in small veins, and in separated lumps of various sizes.
The Mound-Builders worked this copper without smelting it. Spots of pure
silver are frequently found studding the surface of Lake Superior
copper, and appearing as if welded to it, but not alloyed with it. No
other copper has this peculiarity; but copper with similar blotches of
silver has been dug from the mounds. It was naturally inferred from this
fact that the ancient people represented by these antiquities had some
knowledge of the art of mining copper which had been used in the copper
region of Lake Superior. This inference finally became an ascertained
fact.

THEIR ANCIENT MINING WORKS.

Remains of their mining works were first discovered in 1848 by Mr. S. O.
Knapp, agent of the Minnesota Mining Company, and in 1849 they were
described by Dr. Charles T. Jackson, in his geological report to the
national government. Those described were found at the Minnesota mine,
in upper Michigan, near Lake Superior. Their mining was chiefly surface
work; that is to say, they worked the surface of the veins in open pits
and trenches. At the Minnesota mine, the greatest depth of their
excavations was thirty feet; and here, "not far below the bottom of a
trough-like cavity, among a mass of leaves, sticks, and