Geology of Volcanic Islands 371 



the glaciers of that district : but by October (1842) we find him fairly 

 settled at work upon the second volume of his Geology of the Beagle 

 — Geological Observations on tlie Volcanic Islands, visited during 

 the Voyage of H.M.S. "Beagle." The whole of the year 1843 was 

 devoted to this work, but he tells his friend Fox that he could 

 "manage only a couple of hours per day, and that not very regu- 

 larly 1 ." Darwin's work on the various volcanic islands examined by 

 him had given him the most intense pleasure, but the work of writing 

 the book by the aid of his notes and specimens he found "uphill 

 work," especially as he feared the book would not be read, " even by 

 geologists 2 ." 



As a matter of fact the work is full of the most interesting 

 observations and valuable suggestions, and the three editions (or 

 reprints) which have appeared have proved a most valuable addition 

 to geological literature. It is not necessary to refer to the novel 

 and often very striking discoveries described in this well-known 

 work. The subsidence beneath volcanic vents, the enormous denuda- 

 tion of volcanic cones reducing them to "basal wrecks," the effects 

 of solfatarric action and the formation of various minerals in the 

 cavities of rocks — all of these subjects find admirable illustration 

 from his graphic descriptions. One of the most important discussions 

 in this volume is that dealing with the "lamination" of lavas as 

 especially well seen in the rocks of Ascension. Like Scrope, Darwin 

 recognised the close analogy between the structure of these rocks 

 and those of metamorphic origin — a subject which he followed 

 out in the volume Geological Observations mi South America. 



Of course in these days, since the application of the microscope 

 to the study of rocks in thin sections, Darwin's nomenclature and 

 descriptions of the penological characters of the lavas appear to us 

 somewhat crude. But it happened that the Challenger visited most 

 of the volcanic islands described by Darwin, and the specimens 

 brought home were examined by the eminent petrologist Professor 

 Renard. Renard was so struck with the work done by Darwin, 

 under disadvantageous conditions, that he undertook a translation 

 of Darwin's work into French, and I cannot better indicate the 

 manner in which the book is regarded by geologists than by quoting 

 a passage from Renard's preface. Referring to his own work in 

 studying the rocks brought home by the Challenged, he says : 



" Je dus, en me livrant a ces recherches, suivre ligne par ligne les 

 divers chapitres des Observations gfologiques consacrees aux iles de 



1 L. L. i. p. 321. 2 hoc. cit. 



3 Renard's descriptions of these rocks are contained in the Challenger Reports. 

 Mr Harker is supplementing these descriptions by a series of petrological memoirs on 

 Darwin's specimens, the first of which appeared in the Geological Magazine for March, 

 1907. 



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