1866.] BATJERMAN COPPER-MTNES OF MICHIGAN. 451 



with only a few small empty vesicles, the joints being irregularly 

 disposed, giving fragments of no defined forms. Near Eagle Har- 

 bour a well-marked columnar bed is seen, which has been traced for 

 several miles. Another more important bed of a crystalline character 

 occurs a little lower down. This is the so-called "greenstone," a 

 finely crystalline rock without Vesicles, which appears to be nearly 

 homogeneous, and of a dark green colour on a freshly fractured 

 surface ; but a concretionary structure is brought out by weathering, 

 the exposed surface presenting a finely mammillated appearance. 

 The thickness of this bed is from 500 to 800 feet, according to* 

 Whitney ; and where present in force it forms a well-marked feature 

 in the scenery, the escarpment being in fact the " cliif " after which 

 the oldest and most successful of Lake Superior mines is named. It 

 has been traced from the Point eastward for about 40 miles, and is 

 used to divide the mass of the trap into the northern and southern 

 ranges — a distinction that cannot be established in the Portage Lake 

 district, where the greenstone is absent, or covered up with drift. 



Scattered through the massive trap are beds of amygdaloidal 

 character, containing cavities that have been subsequently filled, by 

 infiltration, with foreign minerals, usually zeolite and calcspar, with 

 chlorite, epidote, and native copper in the mineral range ; whereas 

 chalcedonic amygdules, agates, and similar siliceous substances 

 characterize the amygdaloids of the higher or Lake- shore traps at 

 Eagle Harbour, Copper Harbour, and Agate Harbour, &c. 



3. Metallic Minerals of the District. — In addition to the native metal, 

 other copper-bearing minerals have been observed, but only in small 

 quantity : these include a rare substance called Whitneyite (which 

 is the most basic of the known components of copper and 

 arsenic, its composition being represented by the formula, Cu 18, As, 

 with 88-36 per cent, of copper, and 11-64 per cent, of arsenic), 

 copper glance, and the various oxidized ores, such as chryso- 

 colla, malachite, azurite, cuprite, and melaconite. The latter mi- 

 neral, although not of present importance, is of interest as having 

 laid the foundation of mining industry in the country, the first ope- 

 rations of the Cliff Company in 1847 having been upon a vein in the 

 upper conglomerates of Copper Harbour, which produced about 2^ 

 tons of mixed silicates and black oxide of copper, being the only 

 instance in which a deposit of any extent has been found in the top 

 beds. Copper glance has been found in small quantities in a vein 

 at the Huron mine on Portage Lake, and more abundantly at the 

 Mendola mine near Lac la Belle, in the lower or southern portion of 

 the mineral range, which is now being explored in a regular manner. 

 The arsenide occurs in a quartz vein at the Sheldon Columbian mine, 

 and in an unworked deposit on the Lexington location south of 

 Portage Lake, where it has been got in masses of several hundred- 

 weights. This mineral, although rare, is of interest, as it also occurs 

 in the copper-mines of Chili. 



4. Mode of Occurrence of the Copjper. — In addition to its presence 

 in the amygdaloids, copper is found in one of the conglomerates 

 associated with the trap rocks, finely interspersed in the more epi- 



