ECONOMICAL GEOLOGY. 
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mountain. The excavated earth was piled in huge heaps about the mar- 
gins of the pits, and the whole overgrown with the heaviest forest trees, 
oaks and chestnut, some of them three feet and more in diameter, and 
some of the largest belonging to a former generation of forest, growth, 
fallen and decayed ; facts, which indicate a minimum of not less than three 
hundred years.” I added the remark as to the probable origin of these 
pits, “ There is no appearance of a mineral vein and no clue to the object 
of these extensive works, unless it was to obtain the large plates of mica, 
or crystals of kyanite, both of which abound in the coarse granite rock.” 
about two years afterwards in a conversation with Col. Whittlesey, and 
subsequently in numerous publications on the subject of the mounds of 
the northwest, I learned that mica was of common occurrence in the 
tumuli of the Mound Builders, among the utensils and ornaments which 
such rude people are in the habit of inhuming with their dead owners. 
And upon further inquiry I ascertained that cut forms, similar to those 
found in the mounds were occasionally discovered among the rubbish and 
refuse heaps about, and in the old pits. These circumstances revealed un- 
mistakably the purpose and the date of these works, and showed them to- 
be cotemporary with the extensive copper mining operations of Lake 
Superior. 
Since the development of mica-mining on a large scale in Mitchell and 
the adjoining counties, it has been ascertained that there are hundreds of 
old pits and connecting tunnels among the spurs and knobs and ridges of 
this rugged region ; and there remains no doubt that mining was carried 
on here for ages, and in a very systematic and skillful way ; for among all 
the scores of mines recently opened, I am informed that scarcely one has 
turned out profitably which did not follow the old workings, and strike 
the ledges wrought by those ancient miners. The pits are always open 
“ diggings,” never regular shafts ; and the earth and debris often amounts 
to enormous heaps. 
One of the most profitable of all the modern mines, (on Cane Creek), 
is one which is marked by the greatest of the old excavations and the 
largest earth heaps about its margins, in the whole region, showing that 
this was the richest of the ancient diggings. The tunnels are notable as 
being much smaller than such workings in modern mining, being gen- 
erally only three to three and a half feet in height and considerably less 
in width. Some of these tunnels have been followed for fifty and a hun- 
dred feet and upwards. It is asserted by the miners that distinct tool- 
marks are often found along the walls of these tunnels, resembling the 
stroke of a pick or chisel. It is also noticed that the best parts of the 
veins were often abandoned by the old workers, evidently on account of 
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