The Quarterly journal of the Geological Society of London . he foot-wall,and with irregular calcspar strings inthe upper side. Although not produ-cing any very large masses, the yield istolerably uniform, the produce beingat the rate of 1-5 per cent, in thePewabic, and 1-6 per cent, in the Quincy mine: the latter is sunkbelow the 100-fathom level. The concentration of the coppertowards the foot-wall is characteristic of the whole of the amyg-daloids. The other members of the group, below the Pewabic lode, althoughnot of any great importance as regards produce of copper, are ofinterest as estab
The Quarterly journal of the Geological Society of London . he foot-wall,and with irregular calcspar strings inthe upper side. Although not produ-cing any very large masses, the yield istolerably uniform, the produce beingat the rate of 1-5 per cent, in thePewabic, and 1-6 per cent, in the Quincy mine: the latter is sunkbelow the 100-fathom level. The concentration of the coppertowards the foot-wall is characteristic of the whole of the amyg-daloids. The other members of the group, below the Pewabic lode, althoughnot of any great importance as regards produce of copper, are ofinterest as establishing the regular succession of the amygdaloidsover areas of a certain extent, the section being substantially thesame in the Pewabic cross cut as it is in the Albany and Boston lineabout 3^ miles further north. It is not necessary to go further intothe characteristics of these belts or lodes ; but it may be incidentallyremarked that the epidote lode is fiUed with a purplish rock, contain-ing a great deal of bright-green epidote, and that the Albany and. 1866.] BAUERMAN COPPER-MINES OF MICHIGAN. 455 Boston lode is also very epidotic, and in the hollows carries largequartz crystals and masses of prehnite. The Albany and Boston conglomerate is a deposit of considerableinterest, as it forms a well-marked horizon in the rocks of thePortage district, and carries in places a very considerable amount ofcopper. It is about 30 or 32 feet in thickness, and is includedbetween a soft argillaceous sandstone floor, 4 feet thick, and a clayroof of 9 inches in thickness. The latter contains at times parallelsheets of copper, and is locally known as the fluean lode. Thepebbles are chiefly of red jaspideous porphyry, and are for the mostpart well-rounded, varying in size from about half an inch up to sixor eight inches in greatest diameter. The cementing material variesconsiderably, being mainly calcareous at the Pewabic, and a compactepidote at Rhode Island mine. The more usual character^ how
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectgeology, bookyear1845
