Geological Societij. 451 



Cape Fairvveather is near the southern extremity of a range of 

 coast, occupying between two and three degrees on the east of Pata- 

 gonia ; a great part of which is described in the Admiralty Chart, as 

 being "like the coast of Kent, and consisting of steep chalk hills ;" 

 one of the prominences being named, from this supposed resemblance, 

 " Beachy Head." This, however, from Capt. King's statement, 

 would appear to be erroneous : — the whole coast examined by 

 him, was found to be composed of horizontal strata of clay, which 

 may be traced for several miles in unbroken continuity ; the cliffs 

 being from 300 to 400 feet in height, and entirely bare of vegetation. 

 Some of the specimens, however, from this quarter, consist of a white 

 marl, not unlike certain varieties of the lower chalk ; and with these, 

 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 j 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 Frovvard, 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, — 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, 

 being 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 dij) 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 liiat side. 



The specimens from Freshwater Bay, about TJO miles from Ca])e 

 Virgins, on tl>e Patagonian side of the Strait, consist of liigidy crystal- 

 line greenstone and hyperstene rock, resembling those of Scotland ; 

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

 sicnitic rock, quartz and flinty slate. 



3 .M 2 The 



