.834.] ERRATIC BOULDERS. 



247 



height. Some of the icebergs were loaded with blocks of no 

 inconsiderable size, of granite and other rocks, different from the 

 clay-slate of the surrounding mountains. The glacier furthest 

 from the Pole, surveyed during the voyages of the Adventure 

 and Beagle, is in lat. 46° 50', in the Gulf of Penas. It is 15 

 miles long, and in one part 7 broad, and descends to the sea- 

 coast. But even a few miles northward of this glacier, in the 

 Laguna de San Rafael, some Spanish missionaries * encountered 

 " many icebergs, some great, some small, and others middle- 

 sized," in a narrow arm of the sea, on the 22nd of the month 

 corresponding with our June, and in a latitude corresponding 

 with that of the Lake of Geneva ! 



In Europe, the most southern glacier which comes down to the 

 sea is met with, according to Von Buch, on the coast of Norway, 

 in lat. 67''. Now this is more than 20° of latitude, or 1230 

 miles, nearer the pole than the Laguna de San Rafael. The 

 position of the glaciers at this place and in the Gulf of Penas, 

 may be put even in a more striking point of view, for they de- 

 scend to the sea-coast, within 7^° of latitude, or 450 miles, of a 

 harbour, where three species of Oliva, a Yoluta, and a Terebra, 

 are the commonest shells, within less than 9^ from where palms 

 grow, within 4^° of a region where the jaguar and puma range 

 over the plains, less than 21° from arborescent grasses, and 

 (looking to the westward in the same hemisphere) less than 2° 

 from orchideous parasites, and within a single degree of tree- 

 ferns ! 



These facts are of high geological interest with respect to the 

 climate of the northern hemisphere, at the period when boulders 

 were transported. I will not here detail how simply the theory of 

 icebergs being charged with fragments of rock, explains the origin 

 and position of the gigantic boulders of eastern Tierra del Fuego, 

 on the high plain of Santa Cruz, and on the island of Chiloe. 

 In Tierra del Fuego, the greater number of boulders lie on the 

 lines of old sea-channels, now converted into dry valleys by the 

 elevation of the land. They are associated with a great unstrati- 

 fied formation of mud and sand, containing rounded and angular 

 fragments of all sizes, which has originated j in the repeated 



* Agiieros, Desc. Hist, de Chiloe, p. 227. 

 t Geological Transactions, vol. vi, p. 415, 



