THE LOWER HURONIAN. 337 



at others have white weathered surfaces. There occur with the slates at 

 times graywackes which are rather puzzhng. They are more intimately 

 associated with the slates than with the conglomerates, and hence will be 

 described in this place. South of the east end of Moose Lake, and in fact 

 at a number of places on the hills south of this lake, especially in the 

 vicinity of the portage from Moose Lake to Flask Lake, there occurs a 

 graywacke which has a greenish color, and from its green background 

 there stand out very prominent rounded porphyritic feldspars. The 

 appearance is very similar to that of a feldspathic porphyry which occurs 

 in the immediate vicinity of these graywackes. Discrimination between 

 the two is difficult. Li fact, there is evidently a gradation between them, 

 the graywacke representing the disintegrated portion of the porphyry, the 

 particles of which have been but slightly moved and worn. Bedding is not 

 very distinct in it. It is now very schistose, and one can trace the passage 

 from this schistose graywacke into the fairly massive porphyry. 



Somewhat similar feldspathic sediments witli the feldspars appearing 

 almost like phenocrysts occur on the bare hill in the SE. ^ of sec. 16, 

 T. 64 N., R. d W., just west of the southwest end of Newfound Lake. 

 These occurrences correspond very closely to those graywackes which 

 occur at Vermilion Lake (p. 288) in immediate contact with the various 

 acid intrusives, and which in many cases can not be distinguished from 

 them in the field. 



Microscopic characters. — The microscopic examination reveals nothing 

 of especial interest. The essential primary constituents are feldspar, quartz, 

 brown mica, white to green and violet-brown pyroxene, and greenish-brown 

 hornblende, and then there is always an amount of the fine interstitial 

 material, the very fine product of the attrition of the grains of minerals and 

 fragments of rock forming- the slates and graywackes. This material in all 

 cases studied has been recrystallized, and does not show up now as a dark 

 interstitial mass except by low power. By high power the individual con- 

 stituents can usually be recognized and will be referred to below. In the 

 graywackes which are associated with the slates there occur occasional 

 minute fragments of the various rocks which have been mentioned in 

 previous pages as forming a part of the conglomerates. The primary min- 

 eral grains and likewise the interstitial dust have very frequently been 

 extensively altered, and from these have been produced the following 



MON XLV— 03 22 



