RED ROCKS AND DIKES OF THE LESTER RIVER GROUP. 283 
and have serpentine courses, intersecting one another. There can be no 
doubt that the rock and conditions are the same as observed in the case of 
the red rock penetrating the gabbro at Duluth. The red rock below Lester 
River becomes more and more fine-grained as it is followed down the coast, 
until it presents the appearance of a felsite, with distinct red orthoclases. 
Still farther it is much weathered and earthy, with seams of calcite and 
large sized ‘“‘vugs,” lined with fine crystals of the same mineral. In the 
same vicinity it is thickly dotted with amygdule-like spots of white calcite, 
one-fourth inch in diameter. Whether these are true amygdules or replace- 
ments has not been determined. ‘True quartz porphyry and granitic por- 
phyry are exposed along Encampment River in the N. W. 4 of Sec. 11, T. 
53, R. 1 W., with a width of 400 paces. This belt lies at or near the sum- 
mit of the Lester River Group 
Below Lester River these red rocks were observed to be cut by sev- 
eral narrow dikes, 10 to 20 feet wide, and trending N. 45° to 50° E., or 
with the strata. These dikes were marked by a very strong cross-jointing, 
and near the walls by a close-jointing parallel to the walls. In the middle 
of the dikes the rock is black, fine grained, but highly crystalline, and 
rough in texture. ‘Towards the sides where the jointing parallel to the walls 
comes in it is aphanitic, dark-green in color, and greasy from the presence 
of chlorite. A section of the rock from the middle portion shows augite 
predominating, partly fresh, and partly altered to a brownish substance, in 
areas enveloping numbers of minute plagioclases (labradorite), just as in 
the ‘‘luster-mottled” melaphyrs of Pumpelly. Magnetite is present in 
small particles, and besides the viriditic and ocherous material, evidently 
resulting from a change of the augite, there are other particles of some- 
what similar material, usually of a deeper tint, lying between the augites 
in small rounded forms which show no tendency to polarize together. These 
are evidently altered olivines, and the resemblance to Pumpelly’s luster- 
mottled rocks, save in unusual fineness of grain, is thus complete. The 
section of the finer-grained rock from the side of the dike shows it to be 
the same, except that it is in an excessively fine condition, has its augite 
largely changed to a chloritic substance, and contains some non-polarizing 
base. 
