THE QUxVKTZ-SLATE MEMBER. 1(51 



From the section in Sec. tl, T. 45 N.,R. 2 IS., Wisconsin. 



15. Ohloritic slate, from a low horizon underlying 9145 (16). Specimen 9133 

 (.slide 3300). From 1000 N., KJOO VV., Sec. 6, T. 45 N., E. '1 E., Wisconsin. 



A line grained, thinly ck'aval)le, grayish green slate. 



Minute fragments of (juartz and feldspar, the former enlarged in the usual 

 manner, are mingled with a finer material composed of kaolin, sericite, and ferrite. 



10. Ohloritic quart/Jte, from the uppermost horizon. Specimen 9145 (slide 2800). 

 From 1090 N., 1.535 W., Sec. 0, T. 45 N., U. 2 E., Wisconsin. 



A tine grained, vitreous, greenish gray quartzite. 



The thin section is composed mainly of rather small quartz fragments, which are 

 provided, however, with wide and deeply interlocking enlargements. Ohloritic flakes 

 with a little ferrite occur in the interstices of the grains. 



From the West branch of the Montreal section. 



17. Chloritic slate and conglomerate, from the basal portion of the Quartz-.slate 

 member, and in contact with the underlying green schist. Specimens 9149 (slide 

 2912), 9171 (slide 2914). From 175 N., 1035 W., Sec. 27, T. 46 N., K. 2 E., Wisconsin. 



Specimen 9171 contains large pebbles of green schist, cemented by a dark green, 

 uniform grained matrix, iu which an; recognizable numerous grains of quartz, feld- 

 spar, and calcitc. Specimen 9149 is like the matrix of 9171. Tliey are both from the 

 imictioii with tiie underlying greenish schists. 



The slides arc like those described in 12, except that they carry numerous frag- 

 ments of the greenish schist beneath them, and much secondary calcite and chlorite, 

 ])rcsumably derived troni the secondary alteration of the schist fragments. 



IS. Scricitic and chloritic graywackes and graywacke-slates, from the middle 

 horizons. Specimens 9035 (slide 2919), from 190 X., 1130 W.; 9038 (slide 2771), from 

 210 N., lOSO W.; 9040 (slide 2772), from 210 N., 1020 W.; 9043 (slide 2773), fiom 270 

 2^., 1000 W.; 9044 (slide 2774), from 320 N., 1010 W., Sec. 27, T. 46 N., R. 2 E., Wis- 

 consin. 



The rocks are fine grained, compact, of a uniform texture and subconchoidal 

 fracture when broken aci'oss the lamination; are often readily deavable parallel to 

 the lamination, into large thin plates, tiie cleavage surfaces showing the sheen of 

 niicii. The colors vary through siiadcs of green, pink, gray, and purple. 



Tht^ slides differ .somewhat widely in the quantity of fragmental material which is 

 recognizable as such. The finer interstitial material, vaiying from a quite subordinate 

 (|uantity to a iiredominating amount, is composed of Hakes of sericite and chlorite, 

 along with some minutely crystalline quartz and also kaolin and brown iron oxide. 

 The quartz and feldspar fragments occur as in thin sections of similar rock previously 

 described. Tiu' felds])ar particles, while fresh in the inner jiortions, are commonly 

 altered upon the exterior to chlorite and kaolin, which minerals, along with the seri- 

 cite and minutely ci ystalline quartz, are taken to be due to metasomatic changes. 

 MON XIX 11 



