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 the 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.” 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”.” 
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 on 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 petrological 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 Challenger’, he says: 
“Je dus, en me livrant 4 ces recherches, suivre ligne par ligne les 
divers chapitres des Observations géologiques consacrées aux iles de 
12, L.1, p. 321. 2 Loe. cit. 
8 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. 
24—2 
