3. MENOMINEE RIVER. 1ST. STURGEON FALLS GABBRO. From Sturgeon Falls, Menominee River, sec. 27, T. 39 N., R. 29 W., Michigan. Described by Williams, Bull. 62, p. 67. A. Saussurite-gabbro. Contains plagioclase, almost wholly altered to saussurite, diallage, hornblende, and ilmenite, with quartz, calcite, and chlorite as alteration products. B. The same, altered and somewhat schistose. Feldspar much altered into calcite, with secondary quartz and sericite; pyroxene and hornblende changed to chlorite. Leucoxene common. C. Light-gray, silvery schist, derived from gabbro. Contains chlorite, calcite, and a little quartz, with remnants of feldspar. and some leucoxene. Analyses by R. B. Riggs, record Nos. 389, 390, 391. rial dried at 105°. TiO, undetermined. Mate 2D. LOWER QUINNESEC FALLS, MENOMINEE RIVER. Described by Williams, Bull. 62, pp. 89, 91. A. Gabbro-diorite, shore below falls, Wisconsin side. Contains saussurite, hornblende, and ilmenite. Some calcite in the saussurite. Hornblende partly altered to chlorite and ilmenite to leucoxene. B. The same, schistose form. Contains less saussurite. Hornblende and ilmenite completely altered into chlorite and leucoxene. Calcite present, and also porphyritic feldspar. C. Silvery schist, adjoining B, and derived from gabbro. Resembles B in general, without the feldspar crystals. Calcite and sericite are present, and rutile in place of leucoxene. D. Dark, massive greenstone. Contains hornblende, chlorite, epidote, quartz, leucoxene, with some ilmenite and traces of original feldspar. E. Dark, schistose greenstone, forming a band in D. Chlorite entirely replaces hornblende, and rutile replaces leucoxene. Some feldspar, quartz, and calcite. Analyses by R. B. Riggs, record Nos. 384, 385, 386, 387, 388. Material dried at 105°. 3D. UPPER QUINNESEC FALLS, MENOMINEE RIVER. Described by Williams, Bull. 62, pp. 104, 113, 114, 121. A. Light greenstone. Contains hornblende, feldspar much altered to saussurite, ilmenite with leucoxene border, and some secondary quartz. B. Mica-diorite-porphyry. Mainly andesitic feldspar and biotite, with apatite, zircon, sphene, and some calcite. C. Biotite-gneiss, Michigan side. Contains biotite, soda-orthoclase, and quartz. Sphene common, zircon and apatite present. D. Schistose quartz-porphyry. Contains quartz, feldspar, sericite, some chlorite, anatase, and tourmaline, with zircon and apatite sparingly. A, B, and D are from the Wisconsin side of the river. Analyses by R. B. Riggs, record Nos. 392, 393, 394, 395. Material dried at 105°. Talcose-schist. Description, hitherto unpublished, furnished by W. S. Bayley. Analysis by George Steiger, record No. 1835. Consists mainly of talc and quartz, with a little limonite and other iron oxides. 4. PENOKEE-GOGEBIC REGION. Rocks mostly described by Van Hise in Mon. XIX. Analyses A to G by T. M. Chatard, record Nos. 991, 992, 993, 994, 905. A. Diabase, near SE. corner of sec. 13, T. 47 N., R. 46 W., Michigan. Contains plagioclase, augite, magnetite, apatite, and olivine, with some ilmenite and leucoxene. P. R. C. 1001. B. Same dike as A, partly altered. The pyroxene is altered to amphibole, and the latter partly to biotite. Biotite has also been derived from feldspar. P. R. C. 1000. C. Feldspar separated from A. D. Altered diabase, Aurora mine, NE. of SW. of sec. 23, T. 47 N., R. 47 W., Michigan. P. R. C. 1002. |
