] 866.] UAUERMAN COPPEE-MINES OF MICHIGAN. 449 



opened up some new features which have not as yet received any 

 notice, and may be of interest to the Society. 



The copper-mining district of Michigan is situated in the upper 

 peninsula, or north-western portion of that State, forming a nar- 

 row belt of country about 140 miles in length, extending in a 

 north-easterly and easterly direction, from the boundarj'- of the State 

 of Wisconsin to the end of Keweenau Point, the promontory of 

 which projects into Lake Superior on the southern shore, about mid- 

 way between Eond du Lac and the outlet of the lake at Sault S. 

 Marie. 



2. Structure of the District. — The rocks of the district consist of 

 coarse sandstones and conglomerates, occupying either shore, with a 

 central mass of trappean rocks, which forms the mineral range proper. 

 The sandstones on the eastern side have a south-easterly dip, while the 

 traps, which are well stratified, and include several conformable beds 

 of conglomerate, together with the overlying sandstones and conglo- 

 merates of the western and northern shores of Keweenau Point, dip 

 towards the north and north-west, or generally at right angles to 

 the trend of the land. 



The surface of the country is for the most part covered with a 

 dense forest, interspersed with small lakes and swamps. In the 

 drier ground maple is the prevailing timber, with spruce, pine, and 

 oak, in less quantity. Cedar is common in the swamps, which are 

 also remarkable for their profuse growth of enormous plants of 

 Osmunda cinnamomea and other large ferns characteristic of wet 

 ground. 



In the northern district, and as far west as Eagle Eiver, 

 the rocks are free from cover, the sandstones and conglome- 

 rates on the north shore forming a steeply-scarped cliff, sur- 

 mounted by gently sloping inclines on the upper surface of the 

 beds. At Copper Harbour the face of the escarpment of one of 

 the conglomerates is so very regular that, owing to the wood 

 having been burnt off, it may be traced, forming a perfect wall 

 without break, for several miles. Further to the westward, however, 

 the geology becomes very obscure on account of the drift, which ex- 

 tends from near Eagle Eiver to the extreme point of the district 

 beyond the Ontonagon, and, in greater or less thickness, effectively 

 covers up the rocks below. This drift is composed of a stiff blue or 

 reddish clay, passing up into sands or gravels, and in places is full 

 of angular or scratched stones. It is of great thickness in some 

 places — as, for instance, at the Naumkey mine, on the south side of 

 Portage lake, where a shaft was abandoned from excessive influx of 

 water, after 100 feet of sand had been sunk through without reach- 

 ing the rock. Sections of contorted drift are seen in considerable num- 

 bers in the drift plateau which forms the belt of country below the 

 Minnesota hills and the lake-shore near Ontonagon. The surfaces 

 of the rocks immediately below the drift are often scored and striated 

 by ice, the furrows being sometimes of extraordinary size — for in- 

 stance, at the Concord mine, on Portage Lake, where they are nearly 

 semicircular and about 1| inch deep. The general direction of 



