24 On the Geography and Geology 



tlements, and marked, along its mural sides, by deep pilasters. 

 It is a conspicuous object resembling a tower in ruins from a great 

 distance in all directions. 



I have nothing further to add to the topography of the Mam- 

 melles. 



Black Bay, contained by the promontory of the Mammelles and 

 the high lands in the rear of Thunder Hill, may be fifteen miles 

 across at its mouth, and is (as I have been informed by Lieu- 

 tenant Bayfield) 46 miles deep, extremely woody, even to the 

 water's edge, and receives a large river at its bottom. The mouth 

 is guarded by multitudes of woody, and for the most part low, 

 isles. Of their occasional interspaces, the largest is the traverse 

 leading to Thunder-Hill, nearly six miles and a half across ; 

 with one or two islets near each end. The high hills at the bot- 

 tom of Black Bay are visible from the mouth, but a good deal 

 depressed below the horizon. Several islands, apparently large, 

 occupy the centre of the bay. 



From the magnificent headland, called Thunder Mountain, (to 

 which we have now arrived,) to the Grand Portage, leading to the 

 lakes of the north, and to the rich plains bordering on the Rocky 

 Mountains, the distance is 57 miles, measuring along the route of 

 the commercial canoes, which always call at Fort William. This 

 interval consists of one very large bay. Thunder Bay, and a 

 deeply-indented coast, principally consisting of shelving rocks and 

 cliffs, and fronted by groupes of islands. 



Thunder Bay is of a round form, and has a general diameter of 

 1 1 or 12 miles ; Thunder Mountain being its eastern angle, and 

 Grand Point the western. Its west side is low and swampy, and 

 mingles very gradually with the hilly ridges of the interior. The 

 bottom is chiefly in bold declivities, with here and there a scarp 

 of vertical fissures. The eastern side is high, and clothed with 

 small pines, birch, and aspen. At its outer extremity, it rises to 

 the height of 1400 feet in Thunder Mountain, as measured by. 

 Count Adriani *, and I think, accurately, on comparison with 

 other known heights in the lake. 



* Count Adriani, an Italian nobleman, about the year 1800, fitted out a 



