264 



CHARLES DARWIN 



ing 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, 

 explain 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 unstratified formation of mud 

 and sand, containing rounded and angular fragments of all 

 sizes, which has originated 16 in the repeated ploughing up of 

 the sea-bottom by the stranding of icebergs, and by the mat- 

 ter transported on them. Few geologists now doubt that 

 those erratic boulders which lie near lofty mountains have 

 been pushed forward by the glaciers themselves, and that 

 those distant from mountains, and embedded in subaqueous 

 deposits, have been conveyed thither either on icebergs or 

 frozen in coast-ice. The connection between the transportal 

 of boulders and the presence of ice in some form, is strik- 

 ingly shown by their geographical distribution over the earth. 

 In South America they are not found further than 48 0 of 

 latitude, measured from the southern pole ; in North America 

 it appears that the limit of their transportal extends to 53^° 

 from the northern pole ; but in Europe to not more than 40 0 

 of latitude, measured from the same point. On the other 

 hand, in the intertropical parts of America, Asia, and Africa, 

 they have never been observed; nor at the Cape of Good 

 Hope, nor in Australia." 



On the Climate and Productions of the Antarctic Islands. 

 ■ — Considering the rankness of the vegetation in Tierra del 

 Fuego, and on the coast northward of it, the condition of the 

 islands south and south-west of America is truly surprising. 



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



18 1 have given details (the first, I believe, published) on this subject 

 in the first edition, and in the Appendix to it. m I have there shown that 

 the apparent exceptions to the absence of erratic boulders in certain hot 

 countries, are due to erroneous observations; several statements there 

 given I have since found confirmed by various authors. 



