54 THE PENOKEE IRON BEAEING SERIES. 



The lowest member which I have seeu on the Penokee range is a marble, or 

 dolomitif limestone, which we will consider as No. IV. There may be other members 

 below the marble, as is the case in the Huronian rocks of Michigan, but I iiave never 

 found them. 



At the Penokee gap the marble is siliceous; in color light drab to grayish white, 

 with shades of green ; also light red and pink not uncommonly. This diversity of 

 colors is often observable in a hand specimen. The marble is fine grained, and strongly 

 bedded, or massive, depending on the degree of metamorphism. Wheii massive, it is 

 usually jointed, and weathers to a light drab. Some portions of the rock contain 

 pale green to almost white, radiated bunches of actinolite, resembling, in the latter 

 instances, clusters of arragouite 



No. V. Immediately overlying the marble at the (rap is a quartzite, varying in 

 color from grayish white to white, and from saccharoidal to vitreous in texture. It is 

 massive and highly jointed. . . . 



No. VI. Next in order above the (juartzite we have a chloro-siliceous schist. 

 This member was notable for i)reserving its individuality wherever we found it out- 

 cropping, and was therefore easily and ipiickly recognized. It has a dark grayish 

 green color, line grain, and is jointed, and usually more or less slaty. Along the 

 jointing planes it is often liiiely corrugated, and has an unctuous feeling. It cleaves 

 readily into thin pai'allel and wedge-sliai)ed plates. Examined with the lens, it is 

 difficult to distinguish any of the chlorite. . . . 



Nos. VII, IX, aiul probably No. XI, are represented in the near vicinity of the 

 Gap by argillites or black slates, while west of the Gap, from 10 to II miles, as 

 has been alreatly noted, the slates are replaced by diorites and hornblende rocks. 

 My impression is that these slates and greenstones do not vary greatly iu their chem- 

 ical composition, the texture and structure being due to different conditions or 

 degrees of metamorphism. 



The argdlites are brownish to bluish black and have a micro-granular texture. 

 Some of these are quite slaty and cleave freely; others are nuire compact. The slates 

 are thicker and the fracture uneven to conchoidal. On the cleavage i)lanes they have 

 a bright, lively luster, but a fracture across the cleavage is of a dull brownish black. 

 Disseminated through the slate is considerable carbon, which appears ragged under 

 the micros(u)pe. Numerous slender blades resembling microlites of felds])ar are 

 visible. Small angular grains of silica are present; also brownish and slightly 

 dichroitic leaves resembling biotite. 



The diorites, above alluded to as constituting in part Nos. VII and IX of our 

 scheme, are massive and strongly jointed, rarely ever showing any signs of bedding. 

 They are fine to coarse grained in texture; the cleavage planes of the hornblende in 

 coarse varieties being unmistakable; also grains of magnetite. The other mineral 

 ingredients are not so readily distinguished. . . . 



