To the South of the Cove I found a most beautiful Crater, elliptic in form, less than a mile in its longer axis & about 500 ft deep. — Its bottom was occupied by a lake, out of which a tiny Crater formed an Island. — The day was overpowringly hot; & the lake looked blue & clear. — I hurried down the cindery side, choked with dust, to my disgust on tasting the water found it Salt as brine. — This crater & some other neighbouring ones have only poured forth mud or Sandstone containing fragments of Volcanic rocks; but from the mountain behind, great bare streams have flowed, sometimes from the summit, or from small Craters on the side, expanding in their descent have at the base formed plains of Lava. — The little of the country I have yet seen in this vicinity is more arid & sterile than in the other Islands. — We here have another large Reptile in great numbers. — it is a great Lizard, from 10–15 lb in weight & 2–4 ft in length, is in structure closely allied to those imps of darkness which frequent the sea-shore. — This one inhabits burrows to which it hurrys when frightened with quick & clumsy gait. — They have a ridge & spines along the back; are colored an orange yellow, with the hinder part of back brick red. — They are hideous animals; but are considered good food: This day forty were collected.
Note: This appears to be the only mention made by CD, either in the Diary or in his pocketbooks, of the family of finches that came to bear his name and to he most closely associated with the development of his ideas about speciation. However, the relative lack of interest in the Geospizidae displayed by CD when he was actually collecting birds in the Galapagos is consistent with the conclusion that it was not until the Bragle's specimens were classified by John Gould early in 1837 that the true significance of their variability between the individual islands first became apparent to him.
By the time the Journal of Researches was published in 1839, CD no longer believed in the fixity of species, but the most radical of his ideas were still kept strictly to himself. He did not give a great deal away when he wrote: 'It has been mentioned, that the inhabitants can distinguish the tortoises, according to the islands whence they are brought I was also informed that many of the islands possess trees and plants which do not occur on the others. For instance the berry-bearing tree, called Guyavita, which is common on James Island, certainly is not found on Charles Island, though appearing equally well fitted for it. Unfortunately, I was not aware of these facts till my collection was nearly completed: it never occured to me, that the productions of islands only a few miles apart, and placed under the same physical conditions, would be dissimilar. I therefore did not attempt to make a series of specimens from the separate islands. It is the fate of every voyager, when he has just discovered what object in any place is more particularly worthy of his attention, to be hurried from it.
In the case of the mocking-bird, I ascertained (and have brought home the specimens) that one species (Orpheus trifasciatus, Gould) is exclusively found in Charles Island; a second (O. parvulus) on Albemarle Island; and a third (O. melanotus) common to James and Chatham Islands. The last two species are closely allied, but the first would be considered by every naturalist as quite distinct. I examined many specimens in the different islands, and in each the respective kind was alone present. These birds agree in general plumage, structure, and habits; so that the different species replace each other in the economy of the different islands. These species are not characterized by the markings on the plumage alone, but likewise by the size and form of the bill, and other differences. I have stated, that in the thirteen species of ground-finches, a nearly perfect gradation may be traced, from a beak extraordinarily thick, to one so fine, that it may be compared to that of a warbler. I very much suspect, that certain members of the series are confined to different islands; therefore, if the collection had been made on any one island, it would not have presented so perfect a gradation. It is clear, that if several islands have each their peculiar species of the same genera, when these are placed together, they will have a wide range of character. But there is not space in this work, to enter on this curious subject.'
Captain Fitzroy’s Journal
Our first object was to find water: none could be got in the cove, but at a short distance from it a few holes were found, out of which a bottle might be filled in an hour. Around this scanty spring draining continually through the rock, all the little birds of the island appeared to be collected, a pretty clear indication of there being then no other fresh-water within their reach: yet during the rainy season there must be considerable streams, judging by gullies which are worn in the rock. All the heights hereabouts, and the sides of the craters, are composed of sandstone that looks like fine sandy mud half baked; but the low grounds are lava. The crater in which we anchored gave me the idea of its having been a mud volcano.
The climate is very different from that of the Windward Islands; for wind clouds and rain appear to be obstructed in their northward passage, by the heights on the southern part of this island. The heat is here far greater than in other parts of the archipelago, and the land is more sterile. Numbers of another sort of iguana were seen for the first time, and many were killed and eaten. In size and shape they resemble the black kind, but their colour is a dirty orange red, inclining to reddish brown above and yellow beneath. These reptiles burrow in the earth like rabbits, and are not bad eating. Of the black kind a vast number run about the rocks near the sea, living either upon fish or sea-weed. As we went afterwards in a boat along the ragged irregular shore, we saw numbers of turtle. There are small sandy beaches here and there, to which these animals approach in the evenings: when, as it gets dark, they land and usually lie on the beach during the night, even if it is not the season in which they seek a place for their eggs.
From a height near Tagus Cove dismal indeed was the view, yet deeply interesting. To see such an extent of country overwhelmed by lava, to think of the possible effects of the seven dormant volcanoes then in sight, and to reflect that at some one period all was activity and dreadful combustion where we then witnessed only silent desolation, was very impressive.
Note: FitzRoy's ideas had also changed between the return of the Beagle and publication of the Narrative, since following his marriage he had become a firm believer in the absolute truth of the Bible. His view of the significance of the beaks of the finches differed somewhat from CD's, for he wrote: 'All the small birds that live on these lava-covered islands have short beaks, very thick at the base, like that of a bull-finch. This appears to be one of those admirable provisions of Infinite Wisdom by which each created thing is adapted to the place for which it was intended'
In the 1845 edition of the Journal of Researches, the theme of the gradation of the beaks of the ground finches was further expanded, and CD unwrapped his ideas just a little further: 'Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.'