DARWIN ON GALAPAGOS FAUNA 297 



hand, Darwin's* remark that he noticed a few fragments of 

 granite curiously glazed and altered by heat among the ejecta- 

 menta, would seem to imply that the bases of the craters are 

 composed of older forms of eruptive rocks. This supposition 

 is strengthened by an observation made by Professor Suess,t 

 that on the whole of the Pacific coast of America only a single 

 mountain range comes to an abrupt termination on the Pacific 

 coast, namely, the Central American continuation of the An- 

 tillean Cordillera, and that precisely at the point where we 

 might imagine the arcuate prolongation of this chain to meet 

 the principal South American mountains lie the volcanicGala- 

 pagos islands. At any rate, as Dr. Blanford J has pointed 

 out, the rocks of an island may be entirely volcanic, although 

 the island may nevertheless be a remnant of a continental 

 mass. Except that some of the craters have their southern 

 faces broken down, which may be due to some other cause 

 than that suggested by Darwin, the Galapagos islands could 

 just as well represent the mountain tops of sunken land as 

 the summits of originally submarine volcanoes. Neither of 

 these two theories is supported by strong geological evidence. 

 No one was more impressed by this fact than Darwin himself, ' 

 and he bases his theory of the origin of the Galapagos fauna 

 and flora almost entirely on the nature, composition and dis- 

 tribution of the animals and plants he found on the islands. 

 His conclusions were that all the animals and plants must be 

 derived from accidental transport by sea-currents or by birds, 

 except for a few recent immigrants which were introduced by 

 man. 



The natural history of the islands, as Darwin truly remarks, 

 is eminently curious and well deserves attention. Of terres- 

 trial mammals, he says, there is only one which must be con- 

 sidered as indigenous, namely a mouse (Mus galapagoensis). 

 A rat also is sufficiently distinct from the common kind to have 

 been named and described, " but," continues Mr. Darwin, 

 " as it belongs to the Old World division of the family, and as 

 this island had been frequented by ships for the last hundred 

 and fifty years, I can hardly doubt that this rat is merely a 



* Darwin, C, " Journal of Eesearches," pp. 270 — 271. 

 t Suess, E., " Das Antlitz der Erde," II., p. 263. 

 X Blanford, W. T., " Anniversary Address," p. 34. 



