THE QUARTZ SLATE MEMBER. 163 



shows a mixture of fragiiients of quartz and of a minutely crystalline cherty silica, 

 imbedded in a couieut wliich coinitoscs about oue-tliird of the section, and consists of 

 a mixture of very minutely crystalline silica, with particles of chlorite and ferrite. 

 The quartz fragments at times show very distinct secondary enlargements. A few 

 feldspar fragments are seen. 



1'4. Quartzites, from a high horizon. Specimens 9005 (slide 3102), 7620 (slide 

 201(i). From LSHO N., lUlO VV., Sec. 27, T. 47 ii., R. 47 VV., Michigan. 



These are compact, coarse grained, vitreous (juartzites, of a gray color. 



Quartz fragments, with the usual interlocking enlargements, and mingled with 

 some pieces of feldspar, make up most of the sections. The enlargements of the quartz 

 fragments are unusually wide. The outlines of the cores within these enlarge- 

 ments are marked in a distinct manner by films of chlorite and brown iron ore, which 

 minerals also occur along the line of junction between the enlargements of different 

 grains. A number of instances are noted of the enlargement of complex (juartz frag- 

 ments, each individual area within the fragment having received its own enlargement. 



25. Sericitic ferruginous sandstone, from a high horizon. Specimens 9004 (slide 

 2880), 7G18 (slide 2015). From 1880 N., 1910 VV., Sec. 27, T. 47 N., R. 47 W., Michigan. 



Specimen 7018 is nnissive, medium grained, dark reddish brown, and of a sub- 

 vitrcous luster; 9004 is nearer a slate, the quartzitic parts being interstratitied with 

 narrow green belts. 



These slides are intermediate bc^tween the fragmental qiuirtzites and the argil- 

 lu'cuns slates of this mendjer. The fragmental quartz particles still jiredominate, 

 along with some fragmental feldspar, the quartz grains being either without enlarge- 

 ments or with only very iiaridw ones. Contained between the fragments and serving 

 as a matrix to them is a very tine material composed of brown iron oxide, kaolin, 

 minutely crystalline quartz, and chlorite. Numerous Hakes of sericite occur also, ap- 

 pearing rather as if fragmental, or altered from the fragmental mica, than as if sec- 

 ondary to some of the other fragmental constituents of the rock (PI. xix, Fig. 3). 



From the Aurora mine section. 



20. Slaty and cherty iiuartzite, fiom the upi)ermost layers, being the foot wall of 

 the Aurora mine. Specimen 7(il4 (slide 2014). From 024 N., 1000 VV., Sec. 23, T. 47 

 N., R. 47 W., Michigan. 



The thin section slniws an intcrlainination of coarser and liner materials. The 

 coarser bands are coni])osed in about equal quantity of fragments of line ipiartz iiidi- 

 \idn:ils and of :i ciiloritic chert. Tlie finer grained bands are made up of fragments 

 of quartz and feldspar, along with particles of probably secondary silica, chlorite, 

 and iron oxides. 



