THE ANCIENT MINEKS OE LAKE SUPEEIOK. 227 



line quartz, obtained from this mine, and the copper of this district 

 is stated to contain on an average about 3 - 10 per cent, of silver. One 

 mass of copper quarried from the Cliff Mine has been estimated to 

 weigh eighty tons. It was sufficiently detached from its rocky matrix 

 without injuring its original formation, to admit of its dimensions being 

 obtained with considerable accuracy, and it was found to measure 

 fifty feet long, six feet deep, with an average of about six inches in 

 thickness. The total yield of this mine amounted during the past 

 year to sixteen hundred tons of copper, a quantity exceeding, by 

 nearly five hundred tons, the combined product of the other copper 

 mines — eleven in number — of Keweenaw Point, and surpassing by a 

 still greater amount the yield of the Minnesota Mine, the richest of 

 all the works now in operation in the neighboring district of Onton- 

 agon. 



At the Cliff Mine some specimens of the ancient copper tools of 

 the native metallurgists are preserved, but it is to the westward of 

 the Keweenaw Peninsida, that the most remarkable traces of the 

 aboriginal miner's operations are seen. The copper-bearing trap 

 rock, after crossing the Keweenaw Lake, is traced onward in a south- 

 westerly direction till it crosses the Ontonagon E-iver about twelve 

 miles from its mouth ; and at an elevation of upwards of three hun- 

 dred feet above the Lake. At this place the edges of the copper 

 veins appear to crop out in various places, exposing the metal in ir- 

 regular patches over a considerable extent of country. Here, in the 

 neighborhood of the Minnesota Mine, are traces of the ancient mining 

 operations, consisting of extensive trenches, which prove that the works 

 must have been carried on for a long period and by considerable 

 numbers. These excavations are partially filled up, and so overgrown 

 during the long interval between their first excavation and their obser- 

 vation by recent explorers, that they would scarcely attract the atten- 

 tion of a traveller unprepared to find such evidences of former industry 

 and art. Nevertheless some of them measure from eighteen to twenty 

 feet in depth, and in one of them a detached mass of native copper, 

 weighing nearly six tons, was found resting on an artificial cradle of 

 black-oak, partially preserved by immersion in the water with which 

 the deserted trenches had been filled, in the first long era after its 

 desertion. This large mass had evidently been thus disposed prepa- 

 ratory to an attempt at removing it entire. It appeared to have been 

 raised several feet by means of wedges, and then abandoned on ac- 

 count of its unmanageable weight ; and probably portions had after- 

 wards been detached from it, as its surface bore abundant traces of 



