THE QUARTZ-SLATE MEMBER. 173 



between the slate and tlie underlying schists is iinely exposed. The best 

 view of the contact is that oljtained at the foot of the l)ank, where there is 

 a perpendicular cliff of bare rock. The details of the junction shown on 

 this cliff are represented in Figs. 6 and 7. The more southerly rock is a 



f 

 I 



■state ScivLst 



Flo. 6 — .Tunction of <iuartz-slate and green schists at Potato river. 

 Scale: 1 lnch=*20 feet. 



greenish chloritic schist, with a fibrous or parallel structure in a direction 

 almost exactly at right ;nigles to the junction line. The thin sections show 

 it to be probable that this rock was once some sort of a porphyritic eruptive. 

 Whatever its original nature, however, it has certainly been most intensely 

 altered, the minerals having Ijeen rearranged into new condiinations and a 

 parallel structure superinduced. Moreover, this alteration was all carried 

 out previous to the dei)osition against it of the quartz-slate, the lowest layers 

 of which are crowded with fragments from the schist of all sizes, from a fine 

 detritus to blocks several feet in diameter. This exposure, then, shows one of 

 the handsomest iustances of imconformity that we have ever seen, the worn 

 upper surface of the schist being traceable and having fitted into it a finer 

 detrital material belonging to the overlying fragmeutal slate. The accom- 

 panying sketches of this contact were drawn on the ground and represent 

 actual occurrences, the sizes of all the larger fragnients of the conglomerate 

 band being di'iiwu in Fig. 7 to scale, Avliile the structures of the under- 

 lying schists and o\erlying slates are exactly as represented. The junction 

 at the West branch of the Montreal is in all respects similar to thnt on the 

 Potato, except that the exposurt; of the contact is much smaller, and there- 

 fore less satisfactory. The similarity of the rocks at the two places is such 

 as to render it extremely probable that the same contact extends for all the 

 distance between the two streams. 



