. The copper-bearing rocks of lake Superior / by Roland Duer Irving. Geology; Geology; Copper ores; Copper ores. 216 COPPEE-BEAEING EOCKS OF LAKE SUPBEIOR. 100 paces nortli and 1,520 paces west of the section corner, the conglomer- ate forming the southwest bank, and the diabase the northeast, as indi- cated in the accompanying sketches. Figs. 4 and CbnoZomeral/i CI;mu^ Fig. 5.—Cross-section on line CD of Fig. 4. At the last point indicated, B of Fig. 4, the stream makes a sharp turn westward, and the diabase is faulted against a reddish diabase-porphyry, carrying orthoclase and
. The copper-bearing rocks of lake Superior / by Roland Duer Irving. Geology; Geology; Copper ores; Copper ores. 216 COPPEE-BEAEING EOCKS OF LAKE SUPBEIOR. 100 paces nortli and 1,520 paces west of the section corner, the conglomer- ate forming the southwest bank, and the diabase the northeast, as indi- cated in the accompanying sketches. Figs. 4 and CbnoZomeral/i CI;mu^ Fig. 5.—Cross-section on line CD of Fig. 4. At the last point indicated, B of Fig. 4, the stream makes a sharp turn westward, and the diabase is faulted against a reddish diabase-porphyry, carrying orthoclase and triclinic feldspars as porphyritic ingredients, and having- a confused, much altered base in which the minute tabular plagio- clases are, however, very abundant. The whole rock is permeated by ht- tle strings and patches of calcite. Further up the stream, in the northwest part of section 30, and as far as a point 1,675 paces north and 1,590 west of the southeast corner of the Fig. 6.—Section on line AB of Fig. 4. latter section, other basic beds are seen in place, including two or three amygdaloids, some reddish melaphyr and a heavy bed of diabase-porphyry. All of these beds, from the junction of the upper conglomerate, trend north- west and dip northeast 25°. Still further up the stream, in'section 30 (1,420 N., 1,400 W), the true felsitic porphyry begins to show. Judging by the surface width and dip angle, the thickness on this stream between the up- per conglomerate and the last amygdaloid is as much as 600 feet, but some of the apparent thickness may be due to the faultings spoken of The two streams in Sec. 23, T. 51, R. 43 W. do not expose the upper conglomerate, but present above the lower conglomerate some 400 feet in thickness of very regularly-bedded melaphyrs and amygdaloids, including much of an exceedingly fine-grained diabase of the ashbed type, which at times carries numerous porphyritic orthoclases, and runs then into a diabase-. Please note that these image
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectgeology, bookyear1883
