APPENDIX MICROSCOPIC L1THOLOGY. ' 637 



APPENDIX. 



MICROSCOPIC LITHOLOGY, 



BY CHARLES E. WRIGHT. 



[NOTE. The following descriptions are of a small number of crystalline rocks selected from th-i 

 large mass of material on hand, as most 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 bo 

 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 always wholly my own. 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. Silicious Hornblende-Schist. HURONIAN? Black river, Jackson county, 

 north line Sec. %4, T. 21^ R. 4 W. Light-greenish-black; very fine-grained; crystalline 

 texture; eonchoidal fracture; bard 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 aniphibole, minute grains of quartz, and a few 

 scattered leaves of chlorite. From the structure it is evident that the amphibole f ormed 

 after the quartz, since the fonner encloses grains of the latter. 



757. Granite. HURONIAN? Village of Montelln, Marquette county, S. W. qr. 

 Sec. 9, T. 15, R. 10 E. Pale flesh-color, dotted with a few dark patches of mica. The 

 facets of felspar are easily recognized. Traversing the specimen is a thin, light-green- 

 ish 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 bo 

 seen. The grams of quartz are mostly very small and angular, and are frequently 

 enclosed within the 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. HURONIAK? Village of Montello, Marquette County, 

 S. W. 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 grains of 

 silica and a few scales of hematite. 



