of Lake Superior. 



255 



Thunder Mountain is one of the most interesting localities in 

 the lake ; it has been the least studied. I have passed along its 

 south side twice : — at the first time enjoying a transient but near 

 view ; but the second journey was so rapid and distant from the 

 shore that I could only verify the more prominent of my former 

 remarks. I must content myself therefore with a brief detail of 

 the facts actually noted. Limestone, sandstone, conglomerate, 

 amygdaloid, greenstone trap and sienite are close together here ; 

 and in a singular state of disturbance. At the west end of the 

 traverse of six miles and a half from the isle about the mouth of 

 Black Bay to the base of Thunder Mountain, there is a bluff point 

 of rock, a good deal shattered; whose west side, perpendicular 

 and about twenty feet high, has the following appearances. The 

 lowest visible rock (B) is a fine shaly red sandstone of clayey 



base— perhaps four feet thick : it dips with undulation to the 

 E.S.E.? at an angle of 20°, and supports a conformable stratum of 

 limestone (A) from three to four feet thick, light gray, passing 

 into ash brown, compact and fine granular in parts, subdivided 

 into smaller layers, and having small and large interleavings of 

 pale chert. It is without fossils. The rest of the scarp is an 

 amorphous rock (C) red and pale brown in clouds, full of rents 

 in every direction. It is principally of clay ; Avith small knots of 

 white calcspar and a little quartz. It is of sound texture. A few 

 hundred yards hence into the lake are reefs of amygdaloid : and 

 the adjacent hill displays the pilasters of greenstone trap. A sin- 



