312 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
bottom by grooves and striz inclining 5° to 15° away from the vertical, 
towards the north. The red rock of this wall and of the rest of the point 
is a pink to purple felsite, often showing many lines of a lighter color than 
the rest, and seamed with strings and veins of calcite. The bedded dia- 
bases and amygdaloids of the bay seem to have been let down by faulting 
into their present position between the two walls of red rock. 
Beyond this bay to the northeast the felsite of its northern point forms 
the lake coast for about a mile, in which direction it presents a very dis- 
tinct and rather low southeastward dip (15°) with a trend more around to 
the north than that of the lake coast, so that new layers succeed each other 
somewhat quickly, and the total thickness of the felsite mass must be very 
considerable. The general southeastward dip has at times superinduced 
upon ita bowing, by which for short distances the rock will appear to plunge 
underneath the water at a high angle. Calcitic veins, and at times a gen- 
eral calcitic decay, affect the rock in many places, but much of it is with- 
out the calcite. Where the flat lakeward dip is plainest there is often a well- 
marked columnar structure at right angles to the bedding. 
At one point on the shore of the 8. W. 4, Sec. 28, T. 56, R. 7 W., this 
felsite presents somewhat interesting appearances. The ledges here are 
very large, forming a cliff 20 feet high for a distance of many hundred feet, 
with broad surfaces shelving into the water at an angle of about 15°, and 
affected by a strong columnar cross-jointing. The rock of the upper lay- 
ers is aphanitic, but of a rough texture and a flesh color. Thickly dotting 
it are very fine, dark-colored, hair-like lines, forming curves and curls of 
various forms, the whole appearance suggesting strongly that of a thin sec- 
tion of some modern rhyolite or of some glassy rock with hair-like bodies.’ 
Under the microscope this rock is seen to have a matrix which is completely 
saturated with quartz, in the ramifying and network forms which indicate a 
secondary origin. The original matrix appears to have had some minute 
feldspars, but much of it seems to have been without crystalline structure. 
The hair-like bodies resolve themselves into linear clusters of red and black 
particles of ferrite, which I take to be the alteration-product of some orig- 
inal constituent, either crystalline or unindividualized. They are certainly 
‘Compare Zirkel, Microscopical Petrography, Plate VII, Fig. 1, and Plate IX, Fig. 1. 
