Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.3)

ADDENDA. 615 boldt has said (see Cimiers Theory of the Earth, translated by Professor Jameson, p. 346) that they do not occur in Lombardy. I may here re- mark, that care should be taken to separate the phenomenon of great aiigular 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 fL'Institiit, 1838, p. 151 Analysis of the Voyage of the Bonite). I may here add, that M. Puillon Boblaye, in his description of Bone and Constantine on the northern coast of Africa ( L' Institut, 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 little beneath the surface in countries without the