Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.1): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

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 breadth, 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 mterior 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 j and on the surface are lying, strewed about, large oyster-shells. In the clay formation there are two rivers : the Gallegos, in lat. 51° 38' ; and Port Santa Cruz, in lat. 50° T. The Gallegos, at