30 



are portions of a greenish sand-rock, much resembling that of the 

 upper green-sand formation, and of a clay having many of the pro- 

 perties of fuller's earth. The pebbles of the shore consist of quartz, 

 red jasper, hornstone, and flinty slate ; but do not contain any stone 

 resembling chalk flint. 



Cape Virgins at the north-eastern entrance of the Straits of Ma- 

 gellan, consists of clay cliffs, like those of Cape Fairweather ; and 

 between these two Capes the coast is of the same character. 



What may be called the eastern branch of the Straits, from Cape 

 Virgins to Cape Froward, though its general course is from north-east 

 to south-west, varies considerably in width and direction ; but from 

 thence to the western entrance, the direction is nearly straight, from 

 south-east to north-west, — and the width much more uniform : and one 

 of the principal points already determined by Capt. King's survey, is 

 that the fissure constituting this portion of the Strait is continued in 

 the same direction, for about a hundred miles towards the south-east 

 from Cape Froward j through St. Gabriel's Channel, and a deep inlet, 

 discovered by Capt. King and named " Admiralty Sound," which runs 

 nearly fifty miles into the interior of Terra del Fuego. This separation 

 of the land, by a narrow rectilinear channel of such great length, 

 appears to be analogous to the division of Scotland, by the chain of 

 Lochs on the line of the Caledonian Canal. 



In proceeding westward from the eastern entrance, the coast gra- 

 dually changes its character ; and primitive rocks appear about Cape 

 Negro near Elizabeth Island, where mountains of slate rise to the 

 height of from 2000 to 3000 feet. Capt. King remarks that the direc- 

 tion of all the ranges, commencing at Port Famine about thirty miles 

 from Cape Froward, is towards the S.E. • and that all the sounds 

 and openings of the land in Terra del Fuego trend in the same direc- 

 tion ; this being also the direction of the strata, which dip towards 

 the south. This coincidence in the direction of the mountain ranges, 

 has been carefully expressed on Capt. King's map ; and he supposes 

 that a similar structure holds good throughout the western branch 

 of the Strait, from Cape Froward to the entrance on that side. 



The specimens from Freshwater Bay, about 120 miles from Cape 

 Virgins, on the Patagonian side of the Strait, consist of highly crystal- 

 line greenstone and hyperstene rock, resembling those of Scotland ; 

 and the pebbles and boulders on the shore, are of granite, hornstone, 

 sienitic rock, quartz and flinty slate. 



The vicinity of Mount Tarn and Eagle Bay, about midway between 

 Port Famine and Cape Froward, affords also porphyritic and crystal- 

 line rocks, abounding in hornblende, or hyperstene 5 with grauwacke, 

 siliceous slate, and gray splintery limestone. — The slate of Mount 

 Tarn contains traces of organic remains. The specimens from the 

 south side of this eastern branch of the Strait consist of mica-slate 

 approaching to gneiss, found at the entrance of St. Magdalen's Sound, 

 and at Card Point on the south-west of St. Gabriel's Channel. The 

 rocks at Cape Waterfall near Card Point, are of clay-slate 3 and the 

 shores of Admiralty Sound afford granite, and various porphyritic rocks, 

 including clinkstone-porphyry, and greenish compact felspar. Capt. 



