258 On the Geography and Geology 



so, in the same part of a precipice, thus producing a rectangular 

 reticulation on its surface. This sometimes occurs and ceases 

 suddenly, and without the preparatory steps described above. It 

 is well seen at the southside of the west end of Thunder Mountain, 

 in the fine clifTs of the Entredeux, a very beautiful lake, on the 

 old route to the Lake of the Woods, and in many other places. 



In the neighbourhood of Pigeon Bay, this greenstone trap con- 

 tains black flint, so conchoidal, splintery, and of lustre so consi- 

 derable, as to resemble pitchstone. I have only seen it there as 

 debris ; — but it occurs in this rock in horizontal layers, gray and 

 black at the Mountain Fall of the Dog River, according to Major 

 Delafield. This gentleman also found at the Outard Precipice, over- 

 looking the lake of that name in the old route to the Lake of the 

 Woods, small veins of white satin spar, in greenstone trap. 

 Calcspar is a frequent mineral in this rock, in veins and imbedded 

 masses. Its fissures are often filled with quartz crystals — which 

 now and then are amethystine. The slaty trap west of, and con- 

 tiguous to Farther Point, contains oval and circular balls of con- 

 centric layers six and twelve inches in diameter. They are light 

 brown and coarse granular in the centre ; but more compact ex- 

 ternally ; and pass into the ordinary form of the rock by the rapid 

 fading of the discoloured rings marking their successive coats. 



I remarked at Pigeon Point a reddish porphyritic rock ; this 

 Major Delafield, who landed there, has determined to be red 

 granite, but without either hornblende or mica. Further west large 

 grained massive greenstone trap mingles with the slaty form. At 

 Point Chapeau I found the trap in cuboid blocks, with its white 

 feldspar very distinct. 



From distant observation the islands from Fort William to the 

 Grand Portage seem to be trappose, mixed, I do not doubt, with 

 sandstone. The pilasters of the most lofty, such as the Pate, be- 

 speak the nature of their geological structure, while that of the lower 

 isles is explained by the vast quantities of fragments, accumulated 

 on the shores of the main, of simple greenstone trap, amygdaloid, 

 red and white sandstone, white limestone, and the amorphous red 

 rock of the point described in above. 



