354 Darwin and Geology 
is the most southern point where there is much geological interest, 
as there the modern beds end. The Captain then talks of crossing 
the Pacific; but I think we shall persuade him to finish the coast of. 
Peru, where the climate is delightful, the country hideously sterile, 
but abounding with the highest interest to the geologist....I have 
long been grieved and most sorry at the interminable length of the 
voyage (though I never would have quitted it)....I could not make up 
my mind to return. I could not give up all the geological castles in 
the air I had been building up for the last two years’.” 
In April, 1835, he wrote to another sister: “I returned a week 
ago from my excursion across the Andes to Mendoza. Since leaving 
England I have never made so successful a journey...how deeply 
I have enjoyed it; it was something more than enjoyment; I cannot 
express the delight which I felt at such a famous winding-up of all 
my geology in South America. I literally could hardly sleep at 
nights for thinking over my day’s work. The scenery was so new, 
and so majestic; everything at an elevation of 12,000 feet bears so 
different an aspect from that in the lower country....To a geologist, 
also, there are such manifest proofs of excessive violence; the 
strata of the highest pinnacles are tossed about like the crust of 
a broken pie?” 
Darwin anticipated with intense pleasure his visit to the Galapagos 
Islands. On July 12th, 1835, he wrote to Henslow: “Ina few days’ time 
the Beagle will sail for the Galapagos Islands. I look forward with 
joy and interest to this, both as being somewhat nearer to England 
and for the sake of having a good look at an active volcano. Although 
we have seen lava in abundance, I have never yet beheld the crater?.” 
He could little anticipate, as he wrote these lines, the important aid 
in the solution of the “species question” that would ever after 
make his visit to the Galapagos Islands so memorable. In 1832, as 
we have seen, the great discovery of the relations of living to extinct 
mammals in the same area had dawned upon his mind; in 1835 he 
was to find a second key for opening up the great mystery, by 
recognising the variations of similar types in adjoining islands among 
the Galapagos. 
The final chapter in the second volume of the Principles had 
aroused in Darwin’s mind a desire to study coral-reefs, which was 
gratified during his voyage across the Pacific and Indian Oceans. 
His theory on the subject was suggested about the end of 1834 or 
the beginning of 1835, as he himself tells us, before he had seen 
a coral-reef, and resulted from his work during two years in which he 
12. L, 1. pp. 257—58. 2 L. In 1. pp. 259—60. 
3M. L. 1. p. 26. 
