June, 1834. geology. 267 



cessary to look out directly for anchorage ; for fuither inland 

 the depth soon becomes extremely great. Captain Cook, in 

 entering Christmas Sound, had first 37 fathom, then 40, 60, 

 and, immediately afterwards, no soundings with 170. This 

 structure of the bottom, I presume, must arise from the 

 sediment deposited near the mouths of the channels, by the 

 opposed tides and swell; and likewise from the enormous 

 degradation of the coast rocks, caused by an ocean harassed 

 by endless gales. 



The Strait of Magellan is extremely deep in most parts, 

 even close to the shore. About mid-channel eastward of 

 Cape Froward, Captain King found no bottom with 1536 

 feet: if, therefore, the water should be drained off, Tierra 

 del Fuego would present a far more lofty range of mountains 

 than it does at present. I will not here enter on any spe- 

 culations regarding the causes which have produced this 

 remarkable structure, in a district in which the latter move- 

 ments at least have been those of elevation. I may, how- 

 ever, observe, that pebbles, and great boulders of various and 

 pecuhar crystalhne rocks, which have undoubtedly travelled 

 from the south-west coast, lie scattered over the whole of 

 the eastern part of Tierra del Fuego. One enormous block 

 of syenite near St. Sebastian Bay was barn-shaped, and had 

 a girth of 47 feet ; it projected five feet above the sand, 

 and appeared to be deeply buried. The very nearest point 

 to which we can look for the parent rock, is about ninety 

 miles distant. On the shores of the Strait of Magellan, near 

 Port Famine, numerous semi-rounded fragments of various 

 granites and hornblendic rocks are strewed on the beach, 

 and on the sides of the mountain, to an elevation of thirty 

 or forty feet. Now to this point the high road from the 

 Southern and Western shores passes directly over the great 

 abyss of more than 1500 feet deep. Whatever may have 

 been the means of transport, it has not been one of indis- 

 criminate violence : for the two places, St. Sebastian Bay 

 and Shoal Harbour, where the great fragments are most 

 numerous, certainly existed previously to the last and 



