372 Darwin and Geology 



l'Atlantique, oblige que j'^tais de comparer d'une maniere suivie les 

 r^sultats auxquels j'^tais conduit avec ceux de Darwin, qui servaient 

 de controle a mes constatations. Je ne tardai pas a eprouver une vive 

 admiration pour ce chercheur qui, sans autre appareil que la loupe, 

 sans autre reaction que quelques essais pyrognostiques, plus rarement 

 quelques mesures au goniometre, parvenait a discerner la nature des 

 agregats mine>alogiques les plus complexes et les plus varies. Ce 

 coup d'oeil qui savait embrasser de si vastes horizons, penetre ici 

 profondement tous les details lithologiques. Avec quelle sfirete et 

 quelle exactitude la structure et la composition des roches ne sont- 

 elles pas determiners, l'origine de ces masses minerales d^duite et 

 confirmee par l'^tude comparee des manifestations volcaniques 

 d'autres regions ; avec quelle science les relations entre les faits 

 qu'il d^couvre et ceux signaled ailleurs par ses devanciers ne sont- 

 elles pas ^tablies, et comme voici ^branlees les hypotheses regnantes, 

 admises sans preuves, celles, par exemple, des crateres de souleve- 

 ment et de la differentiation radicale des phenomenes plutoniques et 

 volcaniques ! Ce qui acheve de donner a ce livre un incomparable 

 merite, ce sont les id^es nouvelles qui s'y trouvent en germe et 

 jetees la comme au hasard ainsi qu'un superflu d'abondance in- 

 tellectuelle inepuisable 1 ." 



While engaged in his study of banded lavas, Darwin was struck 

 with the analogy of their structure with that of glacier ice, and a 

 note on the subject, in the form of a letter addressed to Professor 

 J. D. Forbes, was published in the Proceedings of the Royal Society 

 of Edinburgh*. 



From April, 1832, to September, 1835, Darwin had been occupied 

 in examining the coast or making inland journeys in the interior of the 

 South American continent. Thus while eighteen months were devoted, 

 at the beginning and end of the voyage to the study of volcanic islands 

 and coral-reefs, no less than three and a half years were given to 

 South American geology. The heavy task of dealing with the notes 

 and specimens accumulated during that long period was left by 

 Darwin to the last. Finishing the Volcanic Islands on February 

 14th, 1844, he, in July of the same year, commenced the preparation 

 of two important works which engaged him till near the end of the 

 year 1846. The first was his Geological Observations on South 

 America, the second a recast of his Journal, published under the 

 short title of A Naturalist's Voyage round the World. 



The first of these works contains an immense amount of informa- 

 tion collected by the author under great difficulties and not un- 

 frequently at considerable risk to life and health. No sooner had 



1 Observations Geologiques sur les lies Volcaniques..., Paris, 1902, pp. vi., vii. 



2 Vol. n. (1844-5), pp. 17, 18. 



! 



