356 Account of the Native Copper . 
copper rock, full of rapids and difficult of asceut. At the di- 
stance of three or four leagues from the lake, it is skirted on 
either side by a chain of hills whose extreme elevation above the 
bed of the Ontonagon. may be estimated at from three to four 
hundred feet. These hills appear to be composed of a nucleus 
of granite, arising through a stratum of red sand-stone, and vo- 
vered by a very heavy deposit of alluvial soil full of water-worn 
fragments of stones and pebbles, and imbedding occasional masses 
of native copper. Such is the character of the country in the 
immediate vicinity of the copper rock, and. the latter is mani- 
festly one of those imbedded substances, which has been for- 
tuitously exposed to the powerful action of the river against an 
alluvial bank. 
During our continuance upon this stream we found, or rather 
procured from the Indians, another mass of native copper weigh- 
ing nine pounds (Troy) nearly; which will be forwarded to the 
War Department. This specimen is partially enveloped by. a 
crust. of green carbonate of copper, which is in. some places 
Jibrous, sud on the under side mixed witha small portion of ad- 
hering sand, and some angular fragments of quartz, upon which 
it appears to have fallen in a liquid state. There is also an ap- 
pearance of crystallization upon one side of it, and a portion of 
adhering black oxide, the nature of which it is difficult to deter- 
mine by ocular inspection. Several smaller pieces, generally 
weighing less than a pound, were also procured during our ex- 
cursion up the Ontonagon, and in the regions east of it; but all, 
excepting those cut from the large mass, are somewhat oxidated, 
or otherwise encrusted upon the surface. The geological struc- 
ture of the country in detail, and the mineral appearances of the 
shore about the copper rock and at other points along the river, 
between that and the lake, are also of a highly interesting cha- 
racter, but do not appear to me to demand a more particular 
consideration in this report. 
The discovery of masses of native copper is generally consi- 
dered indicative of the existenéé of mines in the neighbourhood. 
The practised miner looks upon them as signs which point to 
larger bodies of the same metal in the earth, and is often deter- 
mined, hy discoveries of this nature, in the choice of the spot for 
commencing his labours. The predictions drawn from such 
evidence, are also more sanguine in proportion to the extent of 
the discovery. Jt is not, however, an unerring indication, and 
appears liable to many exceptions. A detached mass of copper 
is sometimes found at a great distance from any body of the me- 
tal, or its ores; and these, on the contrary, often occur in the 
earth, or imbedded in rock strata, where there has been no ex- 
ternal discovery of metallic copper to indicate it. So far as the 
opinions 
