304 TBE PENOKEE IRON-BEARING SERIES. 



disajipearecl and chlorite has become the predoiuiuaiit mineral aside 

 from the quartz and feklspar. At the extreme east end of this area 

 appear the lirst exposures found of the chiy-sUites. Tliese chiy-shites 

 or phyUites differ chiefly from the finer grained grayvvacke shites, into 

 which they grade apparently only in that a portion of their mineral (•(•n- 

 stitueuts are so fine grained as to make exact determinations impossible in 

 many cases. The rocks in the section Ijetween the east range line of 

 R. 1 E. and West branch of the Montreal, the section Ijetween the west 

 branch of the Montreal and Montreal river, and the section at the Montreal 

 river and vicinity extend over a distance east and west of about 6 miles. 

 The westernmost exposure placed in these areas is about 3 miles west 

 of the west branch of the Montreal, while the easternmost exposure is just 

 east of the Montreal river. In this locality the exposures are more numer- 

 ous than in any of the previous ones except those at Bad river and Tylers 

 fork. Also, some of the exposures are of Lirge size. The rocks here 

 included are wholly graywackes and graywacke-slates, which ai-e always 

 chloritic. Only in one or two of them is any biotite found, and 

 then only in subordinate quantity. Some of them are ferruginous in 

 aj)pearance. The slates differ but little from those of the Potato river and 

 Tylers fork sections. Tlie areas west of Black river and at Black river 

 include, with a single exception, all the exposures found in Michigan. 

 They are widely scattered, few in number, and are, with one exception, 

 small. While graywackes and graywacke-slates are found among them, 

 they are very fine grained and approach closely to clay-slates, of which 

 the greater number of the exposures are composed. Mica is found only in 

 a single exposure and in subordinate quantity. 



PetrofjmpMcal charmters of the four types of rock. — In giving a cliarac- 

 terization of the rocks of the Upper-slate member the following order will 

 be followed: (1) The quartzites and conglomerates; (2) The clay-slates or 

 phyllites; (3) The graywackes and graywacke-slates; (4) The mica-slates 

 and mica-schists. This order is that of alteration, the first mentioned being 

 " nearest its original condition of deposition. By following this order the 

 sections will in the main come from exposures in a direction from east to 

 west. 



