580 



GEOLOGICAL REMARKS. 



excepting the shores of the Beagle Channel, which extends from 

 Christmas Sound to Cape San Pio, a distance of a hundred and 

 twenty miles, with a course so direct that no points of the opposite 

 shores cross and intercept a free view through ; although its aver- 

 age breadthj which also is very parallel, is not much above a mile, 

 and in some places is but a third of a mile across. The south shores 

 of Hoste and Navarin Islands are of horn-blende rock, which is 

 also the principal component of the islands in the neighbourhood, 

 as well as of the island itself of Cape Horn. The eastern part of 

 King Charles South Land is low, with plains like the Patagonian 

 coast ; but the range of high land interrupted at Port Famine ex- 

 tends down the north side of Admiralty Sound, and perhaps, with 

 some few intervals, continues to the south-east extremity of the land, 

 near Cape Good Success, which is the south cape of the west side 

 of Strait Le Maire^ and there terminates in lofty mountains covered 

 with snow, one of which, called in the charts * The Sugar Loaf,' is 

 probably four thousand feet high. 



The eastern shore of King Charles South Land, towards the 

 south part, is lofty, but near the northern part is very low. The 

 interior is also low, with extensive plains, abounding with guana- 

 coes, some of which also were found, and shot by the officers of the 

 Beagle, within fifty miles of Cape Horn. 



The eastern coast of Patagonia, from the entrance of the Strait 

 of Magalhaens to the River Plata, is comparatively low. From 

 Cape Virgins to Port St. Julian, where porphyritic claystone com- 

 mences, the coast is formed of clay cliffs, horizontally stratified, 

 and the country is undulating, with extensive plains, or pampas, 

 covered with grass, but without trees. At Port St. Julian, the 

 country becomes hilly, and continues so as far to the northward as 

 latitude 44°, the rock being porphyritic. The clay formation to 

 the southward has been likened to the appearance of the coast of 

 Kent, and at a short distance it bears certainly a very great resem- 

 blance to it; but the cliffs, instead of being of chalk, are composed 

 of a soft marly clay, without any gravel or impressions of organic 

 remains, excepting at Port St. Julian, where fossil shells, both 

 bivalves and univalves, are found imbedded in clay cliffs ; and on 

 the surface are lying, strewed about, large oyster- shells. 



In the clay formation there are two rivers : the Gallegos, in lat. 

 5P 38'; and Port Santa Cruz, in lat. 50° 7'. The Gallegos, at 



