DESCRIPTIONS OF CRITICAL AREAS 205 



escarpment it enters a gateway formed by the edges of one of the diabase 

 sheets, which here rises fully 350 feet above the upper surface of the sedi- 

 ments in which the upper part of the channel of the river is carved., 

 The stream in flowing through the gorge cascades and falls over diabase. 

 Near the foot of the principal falls, about 90 feet below the level of the 

 river above the gorge, greenish dolomites are exposed in the bottom of 

 the channel and the sides are bordered by diabase. Down stream about 

 2 miles from the head of the gorge and probably about 170 feet below it, 

 no further sediments are encountered and the stream channel is located 

 on diabase. Numerous exposures of diabase between this point and 

 Black Sturgeon lake make it seem probable that below the escarpment 

 the whole area is immediately underlain by diabase. Sediments again 

 appear from beneath the diabase not far from the point where the river 

 enters Black Sturgeon lake. There can be no question but that in this 

 locality a diabase sheet (at least 300 feet in thickness) lies along the 

 edge of the cuesta, descends its front, and overlies a very large portion 

 of the lowland in the immediate foreground and probably as far east as 

 Black Sturgeon lake. 



NIPIGON HOUSE OUTLIERS 



Just north of Nipigon House, on the side of a hill of granite porphyry, 

 and covering an area of less than half a square mile, is a small detached 

 mass of diabase lying in a local hollow, the main part of the hill rising 

 behind it. In other hollows on the same ridge are two small patches of 

 basal sandstone and a second area of diabase. On the west end of Jack- 

 fish island, less than half a mile away, diabase is found at water level in 

 immediate contact with the same granite porphyry. 



About 6 miles north of Nipigon House, on the Inner Barn island, in 

 Wabinosh bay, the remnant of the same diabase sheet has a thickness of 

 about 600 feet. On the mainland south of the island other contacts be- 

 tween the diabase and the underlying granite are found, and some boul- 

 ders of granite were also found in the diabase near the bottom of the 

 sheet. 



WABINOSH VALLEY 



About 8 miles northwest of Nipigon House the Wabinosh river enters 

 Wabinosh bay on lake Nipigon. Ascending the Wabinosh river toward 

 the northwest, at Waweig lake, about 8 miles upstream, granites and 

 gneisses are exposed near the shores of the lake and at a number of points 

 in the bottom of the valley in which the river runs for the next 12 miles 

 of its course. On either side diabase bluffs rise to an elevation, in round 

 numbers, of 300 feet above the valley. Ascending these bluffs on the 



