THE UPPER SLATE MEMBEK. 329 



Section east of the west branch of the Montreal and in the vicinity of the Montreal river. 



62. Graywacke-slate, iiciii- base of formation. Specimen DO.'SO (slide 2917), 530 

 N., 1470 W., Sec. 24, T. 4(t N., K. 2 E., Wisconsin. 



The rock is dark brown, tine grained, finely banded, and cleaves readily along 

 the plane of lamination. 



In thin section fragmental (juartz and feldspar in grains of small size compose 

 perhaps one-half of the mass of the rock. The grains of feldspar are mostly much 

 chloritized or kaolinized. The particles of quartz have fre(|uently been enlarged. 

 The abundant tilling material is chlorite, finely crystalline quartz, dark brown oxide 

 of iron, and black iron oxide, a portion of which appears to be magnetite. This rock 

 resend)les very closely the fragmental rocks found at the base of the Upper slate at 

 Black river. 



03. Graywacke-slate, from a lower horizon. Specimen 9166 (slide 2928), 715 N., 

 1700 W., Sec. 24, T. 46 F., R. 2 E., Wisconsin. 



The rock differs from 62 only in being of a dark green color. 



The thin section differs from that of 62 onlj' in that some of the iron oxide is 

 magnetite. 



64. Chloritic graywacke-slate, from a lower middle horizon. Specimen 9026 

 (slide 2SS2), 1350 N., 1000 W., Sec. 22, T. 47 N., R. 47 W., Michigan. . 



The ro(!k is dark greeTiish-gray, very fine grained, and finely laminated. 



In thin section the rock differs from the graywackes Just described chierty in 

 being much finer grained. There is 7nuch fragmental (quartz, and feldspar api)ears, 

 but it is very fine grained, while the matrix is extremely so. 



65. Chloritic graywacke, from a lower middle horizon. Interstratifled with 64. 

 Specimen 9027 (slide 2883), 1350 N., 1000 W., Sec. 22, T. 47 N., R. 47 W., Michigan. 



The rock is gray, medium grained, massive, and breaks with conchoidal fracture. 

 In thin section the rock is a typical graywacke. It differs from that of 54 only 

 in being slightly finer grained and in containi7ig calcite. 



66. (Jhloritic graywacke, from an 'upper middle horizon. Specimen 9163 (slide 

 2925), 1150 N., 1100 W., Sec. 22, T. 46 N., R. 2 E., Wisconsin. 



The rock is like 54. 



In most ])oints this section is like the ]>reviously describeil graywackes. Many 

 of the fragnuMital feldsjiars, however, are large and fresh. They comprise both ortho 

 dase and ])lagioclase, a i)ortion of the latter being microcline. The altei-ation of feld- 

 spar to kaolin or muscovite is nicely illustrated, some of the feldspar aieas coutaiu- 

 iug very nunu'rous flakes. 



67. <!hIoiitic graywacke, from an iii)per horizon. Specimen 9034 (slides 2884 

 and 2918), 555 N., 1445 W., Sec. 14, T. 46 N., R. 2 E., Wisconsin. 



The rock is gray, medium grained, massive, and breaks with conchoidal fnuiture. 



