NORTHWEST O F 



LAKE 



S U P E 11 I 0 R. 



359 



horizontal beds. The dip at this place seems to arise from the upper beds having 

 been deposited on an irregular inclined surface, rather than from any disturbance 

 since their deposition. 



Below the mouth of Split Rock River there is a dike of greenstone, like No. G13, 

 and bearing north 45° east. It is seen for some distance at the small projecting 

 points along the shore, which follows its bearing, but the body of the rock is not 

 cut across by the Lake. The rocks already described continue as far as the point 

 above the mouth of Kanokikopag River, which, as well as the one below, is made 

 by No. 613, bearing northeast and southwest. 



8. Kanokikopag River. — The first rock exposed on this river is about a quarter 

 of a mile from the mouth. It is a soft amygdaloidal shale (No. 288), overlaid by 

 a more compact, thickly-bedded amygdaloid (No. 289). Both rocks dip to the east. 

 The succeeding rock (No. 290) is still more compact, but exhibits, when exposed 

 to the weather, a somewhat fragmentary appearance. The next rock seen is a 

 columnar basalt (No. 291). It contains nests and strings of calcareous spar, and 

 thin veins of argillaceous iron ore (No. 292). At some points the basalt is insinu- 

 ated between the shaly and compact beds. Below it is a bed of No. 290, very 

 much brecciated, and below that again, shaly rock, like No. 288. There is pro- 

 bably a fault near the first exposure of these rocks, by which the basaltic bed is 

 made to dip, apparently, under the metamorphosed beds. It could not be seen, 

 however, in consequence of a clay and marl deposit, which conceals the rocks at 

 the place where it is believed to'occur. As the lower fall is approached, all the 

 beds, which have maintained a southeasterly dip, rise rapidly, and are, finally, bent 

 downwards, and dip to the northwest, as shown in the following section : in which 

 the basaltic bed, beyond the place where the clay deposit occurs, is seen occupying 

 its true position with reference to the metamorphosed rocks. 



About a mile and a half from the Lake the first fall occurs, of five feet perpendi- 

 cular, over a trap-dike, bearing north 30° east and south 30° west. 



Above this dike the red shaly rocks (Nos. 288, 289) increase in thickness, and 

 form a precipitous rapid, the top of which is fifty-five feet above the perpendicular 

 fall just mentioned. The water falls through a narrow gap in the dike, only a few 

 feet in width. 



There is also a north-and-south dike here (No. 618), which cuts through all the 

 rocks on the left side of the river just below the fall. On the right side of the 

 river, the north-30°-east dike is divided, so as to enclose a large mass of No. 289. 

 On the top of the ridge east of the fall, which is one hundred and twenty-nine feet 

 high, No. 289 is associated with altered argillaceous slate (No. 619), and the same 



