ON THE NORTHWEST SHORE OF 



LAKE SUPERIOR. 



417 



18), the seams and joints of which are filled with imperfectly agatized quartz, chal- 

 cedony, and iron ore. The bearing is northeast and southwest, and the dip south- 

 east, at an angle of 7°. A short distance below this is an exposure of quartz rock 

 (No. 19), with seams of quartz running through it. The ridge immediately south 

 of this is composed of hornblendic rock, like that seen on the dividing ridge. It 

 forms perpendicular escarpments on the lake-shore, and is very fissile and decom- 

 posible. The annexed section shows the relations of the rocks at this place. A 



b c 



a. Slaty hornblende. /). Hornblende rook. c. Quartz rook. 



short distance beyond this the hornblende dips to the northwest, is much contorted, 

 and contains numerous thin seams and intercalations of oxide of iron. 



About one-third the distance from the lower to the upper end of the Lake, is a 

 ridge of siliceous slate (No. 231), somewhat chloritic, and rising to the height of one 

 hundred and fifty feet above the level of the water. It bears northeast by east 

 and southwest by west. I could not discover the stratification, unless it agrees with 

 the cleavage, which is 55° south of east. The direction of the joints is 35° north 

 of west. 



At the bend of Flint Lake a ridge of hornblendic rock occurs, massive in some 

 parts, and schistose in others. The schistose portion (No. 22) has intercalations of 

 flinty seams and thin layers of iron ore. The hornblendic rocks here, like those 

 seen north of Mountain Lake, have been disturbed by granitic protrusions (No. 21), 

 large masses of the hornblende (No. 20) being enveloped in the granitic rocks. The 

 syenitic granite rises in rounded ridges to the height of from one hundred and fifty 

 to two hundred and fifty feet. It is rather coarse and felspathic, and weathers with 

 a remarkably rough surface, the other constituents disintegrating, and leaving the 

 quartz standing out in relief. On some of the hills the granitic rocks appear in 

 sloping tabular masses, as though they had been deposited in successive beds, like 

 some of the trap overflows. 



Between Flint Lake and Lake Saganaga, the rocks are all granitic, and resemble 

 those already described. The stream which connects these lakes is divided into 

 numerous channels, at some points, which flow around the granitic knolls, and occa- 

 sionally cut gorges through them, with numerous cascades and picturesque falls. 



This range, continued in a southwesterly direction, would pass in the line of the 

 Missabe Wachu and the Pokegoma Falls of the Mississippi. 



In conclusion, I may here remark that there is perhaps no extinct volcanic 

 region in the world, where trap and other igneous intrusions can be studied to 

 better advantage than in the country bordering on the northwest shore of Lake 

 Superior. Not only are the vertical dikes numerous and conspicuous, but there 

 are abundant examples of overflows, as well as interl animated insinuations, pro- 

 ducing all degrees of metamorphosis on the adjacent strata, graduating from mere 



53 



