THE QUARTZ-SLATE MEMBER. 147 



lying, however, parallel to the beilding, and not lieing- in the nature of the 

 ordinary slaty cleavage. Tliese two characters serve to mai-k this forma- 

 tion so strongly that after once having become familiar with them one is 

 never at a loss to refer its exposures to their true horizon; but while there 

 is this general similarit}' of appearance, there are at the same time a gi-eat 

 many suljordinate phases presented. As macroscopically distinguished, the 

 two most prominent phases are: (1) A thinly slaty, rather soft, usually 

 very tine grained, dark colored kind, having often a distinct tendency 

 toward a greenish tint; and (2) a kind shading into tiie last, ))ut ditlering 

 from it in being harder, and in tending to a ])aler or even light gray color, 

 often showing mica Hakes on the slatv surface, but as often presenting a 

 nearly aphanitic appearance. From the first of these phases there are 

 gradations into (3) a very thinly laminated, highly chloritic, and verv soft 

 kind; while from the second phase there are gradations in one direction 

 into (4) a genuine vitreous quartzite; in another into Q^) a slightly indurated 

 sandstone; and" in a third into ((!) a light gray novaculite. Besides these 

 there are certain phases of relatively rare occurrence. These are (7) 

 red, green, and })urple clay-shales or clay-slates; (S) a conglomerate 

 in which fragments of white chert are imbedded in a greenish chloritic 

 matrix; (H) a magnetitic conglomerate, like the last, but containing 

 a large proportion of magnetite (these last two occur where the formation 

 is in contact with the cherty limest(me); and (10) a peculiar greenish con- 

 glomerate-slate found (mlv on the Potato and West branch of the Montreal 

 rivers, immediately at the contact with an uncontbrmably untlerlying 

 greenish schist. These distinctions are based entirely ujjou the maci'oscopic 

 appearances, which appearances, however, are quite well borne out by the 

 study of the thin sections. The second phase mentioneil includes kinds 

 which prove to have, in addition to the pi-edominaut (piartz, a considerable 

 proportion of a fragmental feldspathic ingredient, to whose jiresence the 

 characteristic whitish to straw-colored weathering is undoubtedly due. 

 The gradations from this phase towards vitreous quartzite arise from a 

 lessening in the amount of the fi'idspathic constituent; those towards novac- 

 ulite from an increase in the proj)ortion of this feldspathic constituent, 

 accompanied by a great decrease in coarseness of grain. The rocks of the 



