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CHAPTER 4

From Plymouth to the Cape Verde Islands

During his first week at sea there was a heavy swell in the Bay of Biscay, and Charles suffered severely from sea-sickness, as he did throughout the voyage, noting gloomily that ‘I often said before starting that I had no doubt I should frequently repent of the whole undertaking. Little did I think with what fervour I should do so. I can scarcely conceive any more miserable state, than when such dark & gloomy thoughts are haunting the mind as have today pursued me.’ It did not help that his thoughts were also most unpleasantly occupied by his having had to witness the flogging of several members of the crew in punishment for their drunkenness on Christmas Day. Fifteen years later he wrote to FitzRoy:

Farewell, dear Fitz-Roy, I often think of your many acts of kindness to me, and not seldomest on the time, no doubt quite forgotten by you, when, before making Madeira, you came and arranged my hammock with your own hands, and which, as I afterwards heard, brought tears into my father’s eyes.⁴⁸

On 31 December the weather was milder, and Charles’s spirits were raised by his first sight of a shoal of porpoises dashing round the vessel, and a stormy petrel skimming over the waves. He spent the afternoon lying on the sofa in the Captain’s cabin, and reading Humboldt’s glowing accounts of tropical scenery, concluding that nothing could be better adapted for cheering the heart of a sea-sick man.

On 6 January 1832 the Beagle arrived at the Canary Islands, and anchored off the port of Santa Cruz on Teneriffe. Although some geographers had adopted the Peak of Teneriffe as a zero point from which to reckon longitude, FitzRoy considered that such a procedure was unsatisfactory because of a lack of data on the precise position of starting points in the neighbourhood of Teneriffe with respect to the Peak itself. However, immediately the anchor had been lowered, a boat carrying the British Vice-Consul and some quarantine officers came alongside with the news that because of reports on the occurrence of cholera in England, nobody would be permitted to land without first undergoing a rigorous twelve days of quarantine. FitzRoy felt that his objective could not be achieved without making observations on shore, and that such a delay was not acceptable, so up came the anchor and the Beagle made sail for the Cape Verde Islands. Knowing of Charles’s unfulfilled plans for an expedition to Teneriffe, FitzRoy wrote:

This was a great disappointment to Mr Darwin, who had cherished a hope of visiting the Peak. To see it – to anchor and be on the point of landing, yet be obliged to turn away without the slightest prospect of beholding Teneriffe again – was indeed to him a real calamity.⁴⁹

The first of Charles’s zoology notes was made off Santa Cruz that day, when he wrote:

The sea was luminous in specks & in the wake of the vessel of an uniform slight milky colour. – When the water was put into a bottle it gave out sparks for some few minutes after having been drawn up. – When examined both at night & next morning, it was found full of numerous small (but many bits visible to naked eye) irregular pieces of a (gelatinous?) matter. – The sea next morning was in the same place equally impure.⁵⁰

Four days later the sea was again very luminous from the presence of myriads of tiny shrimps giving out a strong green light. Charles wrote in his journal:

I proved today the utility of a contrivance which will afford me many hours of amusement & work. It is a bag four feet deep made of bunting; & attached to a semicircular bow this by lines is kept upright, & dragged behind the vessel. This evening it brought up a mass of small animals, & tomorrow I look forward to a greater harvest.⁵¹

This was only the second recorded use, following that of the Irish zoologist J. Vaughan Thompson a few years earlier, of a net specifically designed for the capture of plankton, the name adopted sixty years later for the many kinds of small plants (phytoplankton) or animals (zooplankton) found floating or drifting at various depths in the ocean. Unlike John Coldstream’s oyster trawl, whose lower bar was dragged along the bottom of the sea so that it gathered up the organisms that lived there, Charles’s net was intended to collect from the surface of the water. His notes continue:

11^th. I am quite tired having worked all day at the produce of my net. The number of animals that the net collects is very great & fully explains the manner so many animals of a large size live so far from land. Many of these creatures so low in the scale of nature are most exquisite in their forms & rich colours. It creates a feeling of wonder that so much beauty should be apparently created for such little purpose.

This was indeed a most auspicious beginning, for Charles was far ahead of his time in his instant perception of the significance of plankton in what nowadays would be called the oceanic food web.

During the next few days a number of interesting animals were captured in the net. One of the first was a Portuguese man-of-war, Physalia, a colonial hydrozoan of the order known as siphonophores,^* which have a large horizontal float to hold them at the surface of the sea and long tentacles for capturing their prey. This particular species is well known to swimmers in the warm parts of the North Atlantic for its capability of inflicting a painful sting, as Charles quickly found when he got some of the slime on to his fingers, and on accidentally putting them into his mouth felt the disagreeable sensation, familiar to him, that biting the root of the arum lily produces. There were other hydrozoans such as sea butterflies like the By-the-Wind Sailor Velella, with a small sail on its upper surface, some salps growing in long chains, and ‘a very simple animal’ of which Charles produced an excellent picture on the first page of the twenty plates that he drew under his Bancks microscope to illustrate his Zoology Notes. He later found more of these creatures off the coasts of Brazil and Patagonia, where he described their anatomy in greater detail, but he had still not succeeded in classifying them when the Beagle returned to England in 1836. Today they are instantly recognisable as arrow-worms of the genus Sagitta, powerful carnivorous predators on other planktonic animals, which are seized by grasping spines located on either side of the head. They are plankton common in all tropical seas, but they had only been formally named in 1827, in a paper that was not in the Beagle’s library.

On the Beagle’s arrival at St Jago (São Tiago on a modern map) in the Cape Verde Islands on 16 January, Charles divided his time between geology in the mornings, collecting the animals that he found on the seashore in the middle of the day, and examining his specimens and writing his notes in the evening. With FitzRoy and the First Lieutenant John Wickham he visited St Jago’s famous baobab tree of legendary age, whose height was measured with naval accuracy both by triangulation and by being climbed by the Captain and letting down a string from the top. The marine wildlife included a variety of sea slugs (Doris), sea hares (Aplysia), sea urchins, sea anemones, shells, turbellarian flatworms, and some corals, but the highlight was Charles’s encounter with an octopus, of which he wrote:

Found amongst the rocks West of Quail Island at low water an Octopus. When first discovered he was in a hole & it was difficult to perceive what it was. As soon as I drove him from his den he shot with great rapidity across the pool of water, leaving in his train a large quantity of the ink. Even then, when in shallow place it was difficult to catch him, for he twisted his body with great ease between the stones & by his suckers stuck very fast to them. When in the water the animal was of a brownish purple, but immediately when on the beach the colour changed to a yellowish green. When I had the animal in a basin of salt water on board this fact was explained by its having the Chamælion like power of changing the colour of its body. The general colour of animal was French grey with numerous spots of bright yellow. The former of these colours varied in intensity, the other entirely disappeared & then again returned. Over the whole body there were continually passing clouds, varying in colour from a “hyacinth red” to a “Chesnut brown”. As seen under a lens these clouds consisted of minute points apparently injected with a coloured fluid. The whole animal presented a most extraordinary mottled appearance, & much surprised every body who saw it. The edges of the sheath were orange, this likewise varied its tint. The animal seemed susceptible to small shocks of galvanism: contracting itself & the parts between the point of contact of wires, became almost black. This in a lesser degree followed from scratching the animal with a needle. The cups were in double rows on the arms & coloured reddish. The eye could be entirely closed by a circular eyelid, the pupil was of a dark blue. The animal was slightly phosphorescent at night.⁵²

Charles was greatly excited by what he thought was a new discovery, and described it enthusiastically in his first letter to Henslow. But Henslow replied that he too had seen the colour changes of an octopus he had caught at Weymouth, and that the phenomenon had also been reported by others. Cuvier had indeed mentioned the ability of an octopus to outdo a chameleon in this respect, but Charles was nevertheless the first to give an accurate description of the properties of its chromatophores, the pigment cells in the skin whose rapid contraction and expansion under nervous control are responsible for the vivid colour changes in octopus and other cephalopods such as cuttlefish and squid. Their function is not only to camouflage the animals when they move to new surroundings, but as has only been appreciated very recently, to provide a means of communication between them.

In his Autobiography, Charles wrote:

The investigation of the geology of all the places visited was far more important than natural history, as reasoning here comes into play. On first examining a new district nothing can appear more hopeless than the chaos of rocks; but by recording the stratification and nature of the rocks and fossils at many points, always reasoning and predicting what will be found elsewhere, light soon begins to dawn on the district, and the structure of the whole becomes more or less intelligible. I had brought with me the first volume of Lyell’s Principles of Geology, which I studied attentively; and this book was of the highest service to me in many ways. The very first place which I examined, namely St. Jago in the Cape Verde Islands, showed me clearly the wonderful superiority of Lyell’s manner of treating geology, compared with that of any other author whose works I had with me or ever afterwards read.

His copy of Volume 1 of Lyell’s Principles was inscribed ‘Given me by Capt. F.R. C.Darwin’, and he had been advised by Henslow to read it ‘but on no account to accept the views therein advocated’.

Charles’s first geological project was to examine the structure of Quail Island, which as it happened was painted by the artist Conrad Martens about eighteen months later, on his way out to join the Beagle at Monte Video (see Plate 1). It was a ‘miserable desolate spot less than a mile in circumference’ in the harbour of Porto Praya, but served Charles usefully as a key to the structure of the main island of St Jago. He wrote in his Autobiography:

The geology of St Jago is very striking yet simple: a stream of lava formerly flowed over the bed of the sea, formed of triturated recent shells and corals, which it has baked into a hard white rock. Since then the whole island has been upheaved. But the line of white rock revealed to me a new and important fact, namely that there had been afterwards subsidence round the craters, which had since been in action, and had poured forth lava. It then first dawned on me that I might perhaps write a book on the geology of the various countries visited, and this made me thrill with delight. That was a memorable hour to me, and how distinctly I can call to mind the low cliff of lava beneath which I rested, with the sun glowing hot, a few strange desert plants growing near, and with living corals in the tidal pools at my feet.

In the notes made at the time Charles’s interpretation was that both islands were volcanic, and had at some not too distant time been submerged beneath the sea, where they quietly collected beds of marine material, followed by another layer of molten lava.⁵³ ‘The whole mass was then raised, since which or at the time there has been a partial sinking. I judge of this from the appearance of distortion, & indeed the distant line of coast seen to the East, which is considerably higher, bears me out.’

This was accompanied by a section drawing of Quail Island showing the successive layers. Tests on specimens from the white layer D showed that it ‘Effervesces readily with Mur: Acid, gives precipitate with Oxalate of Ammonia. – Under Blowpipe becomes slowly caustic, & with heat Cobalt remains of a Violet colour. – Carbonate of Magnesia. (?) Carb. of Lime.’ (The white line may be seen in Plate 1.)

In his first independent geological project, Charles’s careful analysis of the sequence of rocks in Quail Island showed with what great effect he had followed the teaching of Sedgwick and Henslow. His notes also reveal how geology allowed him from the start to exercise to the full his latent passion for argument and theorisation. On completing his notes on Quail Island, he immediately reread them and wrote, ‘I have drawn my pen through those parts which appear absurd,’ and a year later he added a long list of further comments and theories. At the same time he immediately fell in wholeheartedly with Lyell’s gradualist and not yet generally accepted approach that geological changes resulted from slow processes operating over a long period of time. Thus his evidence clearly supported the view that both subsidence and elevation of the land must have taken place over an appreciable area in the not too distant past, and he was led to agree with Lyell that the forces involved might act slowly and evenly so as to leave superficial features of the landscape and buildings undisturbed. Another relevant factor in the story was Charles’s identification of the dust that thickly coated the ship throughout their visit to St Jago, ‘to the great injury of fine astronomical instruments’, as volcanic in origin.

Charles reacted to his first day on St Jago with the enthusiasm that never deserted him:

I returned to the shore, treading on Volcanic rock, hearing the notes of unknown birds, & seeing new insects fluttering about still newer flowers. It has been for me a glorious day, like giving to a blind man eyes – he is overwhelmed with what he sees & cannot justly comprehend it. Such are my feelings, & such may they remain.