146 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
phyrs, are met with at a number of points on the North Shore between Du- 
luth and Saint Ignace Island, south of Nipigon Bay. 
One of the most instructive occurrences of true quartz-porphyry that 
I have yet met with throughout the entire lake basin is at the Great 
Palisades, on the Minnesota shore, six miles below the little hamlet of 
Beaver Bay, See. 22, T. 56, R. 7 W. The Palisades, which constitute the 
most striking feature of North Shore scenery between Duluth and Pigeon 
River, rise in a sheer precipice from the water's edge to a height varying from 
150 to 300 feet. The length of the precipice, whose main front looks 
southeast by east, and runs almost exactly with the general trend of the 
strata in the vicinity, is about three-fourths of a mile. At the north end, 
at the mouth of Palisade Creek, the cliff turns to the westward, and facing 
first north, and then west, is nearly as difficult in ascent in the woods as on 
the lake front. At the south end the shore of the lake runs back with an 
east and west course, in such a manner as to expose the mass, with the 
underlying rocks, in cross-section. The same underlying rocks are cut 
down into by Palisade Creek below the west cliff, so that the Palisade rock 
is a detached mass of porphyry three-fourths of a mile long, one-fourth 
wide, and from 300 to 400 feet thick. 
The Palisade porphyry is a hard and dense = purplish-red on a 
fresh fracture, weathering to a light-red and even pink on the face of the 
cliff. The matrix is thickly studded with sharply outlined, white and par- 
tially kaolinized orthoclase crystals, running up to 0.15 inch in length, and 
somewhat rarer and smaller black quartzes. In many cases the matrix 
shows a fine banding, due to faint differences in shades of color, lighter 
colored laminz appearing to alternate with darker. Sometimes these appar- 
ent lamin are more definite, and from one to two-tenths of an inch in 
width. More commonly they are exceedingly indefinite, and due to rows 
of lighter-colored indefinite spots following one direction. Only rarely does 
the hand specimen show this lining plainly, but on the exposed and weath- 
ered surfaces it stands out prominently. In some places a decomposition 
akin to kaolinization has followed these lines on weathered surfaces, and 
then there is a cleavage parallel to them, and the resemblance to a material 
of sedimentary origin is still more pronounced. The lines preserve only a 
