166 THE PENOKEE IRON-BEAKING SERIES. 



These rocks resemble closely 9038 to 9044 of 18. The sheen of hydro-mica is less 

 marked thiin in those rocks. 



The fraginental particles of quartz and feldspar, of which these sections are 

 mainly composed, are more rounded and larger than in 2771 and 2774 of 18, to which 

 in all other respects these rocks are closely similar. The enlargements of the quartz 

 fi-agments are broad and well marked. In 3071 chlorite appears to be the chief 

 interstitial material; in 3072 the chlorite is mingled with much kaolin and minutely 

 crystalline silica. (PI. xviii, Figs. 1 and 2.) 



37. Vitreous quartzites, from near the top of the (iuartz-slate member. Speci- 

 mens 9440 (slide 3009), from 4.W N., 162.'> W.; 9441 (slide 3070), from 400 N., 102.5 W., 

 Sec. 10, T. 47 N., 11. 45 W., Michigan. 



The rock 9440 is compact, gray, and coarse grained, while 9441 is line grained 

 and pink. Both break with a conchoidal fracture. 



The thin section 30(i9 furnishes a beautiful illustration of the true nature of the 

 ordinary vitreous quartzite; the large and deeply interlocking areas of quartz which 

 mostly compose it having each its plainly outlined fraginental core. These cores are 

 outlined particularly by the broad Alms of the chlorite and limonite witli wliich they 

 are furnished. Slide .•'>070 differs from .3009 only in being much finer grainerl and in 

 having mingled with the quartz a good deal of fragmental feldspar. 



From the section in the adjoining portions of Sees. 10, 15, and 14, T. 47 N., B. 45 



W., Mlclngan. 



38. Sideritic and chloritic schists, from the bottom of the Quartz-slate member, 

 immediately beneath the succeeding number. Speciniens 12545 (slide 5337), 125'46 

 (slide 5338). From 1975 N., 800 W., Sec. 15, T. 47 N., li. 45 W., Michigan. 



The rocks are greenish gray, fine grained, and have a well developed fibrous 

 structure. They show lamination only by somewliat difdcult and irregular parallel 

 fracture. Contained in the fine material are numerous larger grains of feldspar. 



While the thin sections have a strongly crystalline appearance, they show that 

 the rocks are unnnstakably fragmental. Fragments of quartz and feldspar of medium 

 size are contained in a (ine grained matrix of a very complex character. The clastic 

 quartz and feldspar are in part well rounded, but most of the grains are jiuitc angular, 

 indicating the probability that they are near their original source. Some of the quartz- 

 grains are distinctly enlarged. Many of the feldspar fragments are much altered, 

 the resultant products being chlorite, kaolin, sericite, and inobably quartz. A few 

 rounded complex fragments from a basic eruptive are present. Tiic matiix of the 

 sections is a finely complex mass of quartz, felds]>ar, chlorite, sericite, kaolin, and a 

 little ferrite. 



