. The copper-bearing rocks of lake Superior / by Roland Duer Irving. Geology; Geology; Copper ores; Copper ores. 294 COPPER-BEAEING EOCKS OF LAKE Tt^sle^ Zz?z-^ of the Greenstone of Keweenaw Point. It consists chiefly of very fresh augite in relatively large areas, inclosing numbers of tabular plagioclases (an- orthite), and having in the inter- spaces, which are chiefly occupied by the same tabular plagioclases, many small altered olivines and particles of magnetite. The dike is strongly cross-jointed, save at the edges, which are traversed by joints parallel to the walls, and are
. The copper-bearing rocks of lake Superior / by Roland Duer Irving. Geology; Geology; Copper ores; Copper ores. 294 COPPER-BEAEING EOCKS OF LAKE Tt^sle^ Zz?z-^ of the Greenstone of Keweenaw Point. It consists chiefly of very fresh augite in relatively large areas, inclosing numbers of tabular plagioclases (an- orthite), and having in the inter- spaces, which are chiefly occupied by the same tabular plagioclases, many small altered olivines and particles of magnetite. The dike is strongly cross-jointed, save at the edges, which are traversed by joints parallel to the walls, and are com- posed of an aphanitic rock, much altered to chlorite. The rocks tra- versed are the usual stratiform Fig. 15.—Dike traversing stratiform amygdaloid and amygdaloid and Columnar mola- columnar melaphyr, two miles below Lester Eiver, r- i a -r> r~i Minnesota coast. phyr ol the Agate liay Uroup. Equivalents of the Duluth, Lester Biver, and Agate Bay Groups at the east end of the Minnesota coast.—At the eastern end of the Minnesota coast there intervenes, between the Huronian slates and the base of the Beaver Bay Group, which next overlies the Agate Bay beds, a space only three and a half miles wide, measured at right angles to the east and west strike. With the flat dip prevalent in this region this width cannot include a total thickness of more than 3,000 feet, while at the Duluth end of the coast there lie between the same horizons the whole of the Duluth, Lester Eiver, and Agate Bay groups, a thickness of some 9,000 feet; not to speak of the Duluth gabbros, which must add several thousand feet more. Forty miles west of Grand Portage, however, about Brul^ Lake, in T. 63, R. 2 W". and R. 3 W., the gabbros are present in full force, while between them and the lower limit of the Beaver Bay Group there is a width of 10 miles, within which space, supposing the dip to be not more than 10°, a figure which the observations along Cascade River show to be closely right, t
Size: 1567px × 1594px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, booksubjectgeology, bookyear1883
