ADDENDA. 



615 



boldt has said (see Cuvier's Theory of the Earth, trmislated hy Professor 

 Jameson, p. 346) that they do not occur in Lombardy. I may here re- 

 mark, that care should be tai<:en to separate the phenomenon of great 

 angular blocks, from that of rounded ones, although of considerable 

 size ; for torrents, and more especially the waves of the sea, during 

 its slow oscillation of level, are agents sufficiently powerful to produce 

 great effects. The lowest latitude in South America, in which I found 

 large angular fragments, which must have been transported by ice there 

 formed, or by some unknown means, was in latitude 41°. But as I did 

 not examine the country immediately north of it, I am not prepared to 

 say that this is their extreme limit ; but between latitude 27° and 33°, I 

 found no appearance, on either side of the Cordillera, which indicated a 

 power of transportation of the kind required to remove boulders from a 

 distance. Thus, we find that the limit of their dispersion in the two 

 Americas is nearly the same; although they approach the warmer zones 

 rather more closely in the northern than in the southern division of the 

 continent, and in both, probably, more so than in Europe. 



In the note, in which I have considered the apparent exceptions to the 

 law, that erratic boulders are not found in the intertropical regions, I 

 have said that the internal evidence of the Macao case led me to doubt its 

 reality, and I now find it is distinctly stated by M. Chevalier that the 

 rounded blocks result from the secular disintegration of the fundamental 

 rock f L'Institut, 1&S8, p. 151 — Analysis of the Voyage of the BoniteJ. I 

 may here add, that M. Puillon Boblaye, in his description of Bone and 

 Constantine on the northern coast of Africa (UBtstitut, 1838, p. 248, 

 says, " Je n'ai rien vu que put indiquer le phenomene des blocs erratiques." 

 My statement that erratic boulders are not found in Australia, is fully 

 borne out by information communicated to me by Major Mitchell, who, 

 in his repeated expeditions, has traversed so much of the south-east divi- 

 sion of that continent. With the several facts given here and in the 

 Journal (p. 289), I can scarcely doubt that the law of the distribution of 

 erratic blocks is finally determined ; and it is needless to specify the great, 

 not to say conclusive, importance of this law on the theory of the means 

 of their transportation, — a problem which has so long perplexed 

 geologists. 



Page 294. 



In my discussion on the climate of the southern hemisphere, I have 

 shown that a low altitude of the line of perpetual snow, and consequently 

 the descent of glaciers to the level of the sea in latitudes relatively low to 

 what occurs in the northern hemisphere, and likewise the perpetual con- 

 gelation of the soil a httle beneath the surface in countries without the 



