[312] 



DARWIN AND HUMBOLDT. 



treatise alone would have placed Dar- 

 win in the very front of investigators 

 of nature. 



The second part was entitled 

 Geological Observations of the 

 Volcanic Islands visited during the 

 Voyage of H. M.S. Beagle, together 

 with some Brief Notices on the 

 Geology of Australia and the Cape 

 of Good Hope (1844). Full of de- 

 tailed observations, this work still 

 remains the best authority on the gen- 

 eral geological structure of most of 

 the regions it describes. At the time 

 it was written, the " Crater of Eleva- 

 tion theory," though opposed by 

 Constant, Prevost, Scrope, and 

 Lyell, was generally accepted, at 

 least on the Continent. Darwin, 

 however, could not receive it as a 

 valid explanation of the facts, and 

 though he did not adopt the views of 

 its chief opponents, but ventured to 

 propose a hypothesis of his own, the 

 observations impartially made and 

 described by him in this volume must 

 be regarded as having contributed 

 toward the final solution of the ques- 

 tion. 



The third and concluding part bore 

 the title of Geological Observations 

 on South America (1846). In this 

 work the author embodied all the 

 materials collected by him for the 

 illustration of South American geol- 

 ogy save some which had already 

 been published elsewhere. One of 

 the most important features of the 

 book was the evidence which it 

 brought forward to prove the slow 

 interrupted elevation of the South 

 American Continent during a recent 

 geological period. On the western 

 sea-board he showed that beds of 

 marine shells could be traced more or 

 less continuously for a distance of 

 upward of 2,000 miles, that the 

 elevation had been unequal, reaching 

 in some places at least to as much as 

 1,300 feet, that in one instance, at a 

 hight of 85 feet above the sea, un- 

 doubted traces of the presence of man 

 occurred in a raised beach, and hence 

 that the land had there risen 85 feet 

 since Indian man had inhabited Peru. 



These proofs of recent elevation may 

 have influenced him in the conclu- 

 sion which he drew as to the marine 

 origin of the great elevated plains of 

 Chili. But at that time there was a 

 general tendency among British geol- 

 ogists to detect evidence of sea-action 

 everywhere, and to ignore or minimize 

 the action of running water and wind- 

 drift upon the land. An important 

 chapter of the volume, devoted to a 

 discussion of the phenomena of cleav- 

 age and foliation, is well known to 

 every student of the literature of 

 metamorphism. 



The official records of the Beagle 

 did not, however, include all that 

 Darwin wrote on the geology of the 

 voyage. He contributed to the Trans- 

 actions of the Geological Society 

 (vol. v. 1840) a paper on the connec- 

 tion of volcanic phenomena. In the 

 same publication (vi. 1842) appears 

 another, on the erratic boulders of 

 South America ; while a third, on the 

 geology of the Falkland Islands, was 

 published later 



While dealing with the subterrane- 

 an agents in geological change, he 

 kept at the same time an ever wach- 

 f ul eye upon the superficial operations 

 by which the surface of the globe is 

 modified. He is one of the earliest 

 writers to recognize the magnitude 

 of the denudation to which even recent 

 geological accumulations have been 

 subjected. One of the most impres- 

 sive lessons to be learnt from his 

 account of Volcanic Islands is the 

 prodigious extent to which they have 

 been denuded. As just stated, he 

 was disposed to attribute more of this 

 work to the action of the sea than 

 most geologists would now admit; 

 but he lived himself to modify his 

 original views, and on this subject his 

 latest utterances are quite abreast of 

 the time. It is interesting to note that 

 one of his early geological papers was 

 on the Formation of Mould (1840), 

 and that after the lapse of forty years 

 he returned to this subject, devoting 

 to it the last of his volumes. In the 

 first sketch we see the patient observ- 

 ation and shrewdness of inference so 



