Wisconsin. Chief Geologist / Geology of Wisconsin. Survey of 1873-1879 ...
Volume II (1877)
Appendix. Microscopic lithology, pp. 637-642 ff. PDF (2.0 MB)
APPENDIX -MICROSCOPIC LITHOLOGY. 637T APPENDIX. MICROSCOPIC LITHOLOGY. BY CHA1RLES E. WRIGHT. [NOTE. -The following descriptions are of a small number of crystalline rocks selected from the large mass of material on hand. as rmost difficult to determine, or as having a special importance. The numbers are the same as given in the body of the report, and the original specimens will be found in the survey collections, when distributed. A few of Mr. Wright's descriptions have been made use of in the foregoing pages, but the descriptions of crystalline rocks there given are nearly alwaays wholly my owln. It is a matter of regret that the funds were not available for micro- scopic examination of a full suite of the Central Wisconsin rocks. R. D. I.] 501. Silicions Hornhlende-Schist. HuiRoNIAN? Black ricer, Jackson county, north 1ine Sec. 14, T. 212 R. 4 W. Light-greenish-black; very fine-grained; crystalline texture; conchoidal fracture; hard and compact. With the lens, minute grains of silica are plainly visible, but the ingredient minerals cannot be distinguished. Under the mi- croscope, in the polarized light, a thin section of the rock presents a very pretty field, and is composed of small fragments of amphibole, minute grains of quartz, and a few scattered leaves of chlorite. From the structure it is evident that the amphibole formed after the quartz, since the former encloses grains of the latter. 757. Granite. HURONI tN? Village of Montello, Marquette county, S. W. qr. Sec. 9, T. 15, R. 10 E. Pale flesh-color, dotted with a few dark patches of mnica. The facets of felspar are easily recognized. Traversing the specimen is a thin, light-green- isle seam of what appears to be epidote. Under the microscope, in the polarized light, the coarse fragments of orthoclase apparently constitute more than one-half the en- tire section. An occasional twin crystal of felspar after the Carlsbad form may be seen. The grains of quartz are mostly very small and angular, and are frequently enclosed within tbe felspar. With a power of 500 diameters are visible, in the quartz, fluid inclusions; the absence, however, of any glass or stone-filled cavities will no doubt refer the rock to a metamorphic origin. 758. Argillo-chloritic Schist. HURONIAN? Village of Montello, MVar-quette Counity, S. TV. qr. Sec. 9, T. 15, R. 10 E. Grayish-green; fine-grained texture; partially decom- posed; cleaves readily into irregular plates; in the joints it is often ocherous; under the microscope the pale greenish leaves of chlorite are plainly visible; also minute grain-s of silica and a few scales of hematite.
Based on date of publication, this material is presumed to be in the public domain.| For information on re-use see: http://digital.library.wisc.edu/1711.dl/Copyright