Information Category | 08-03-08 02:40 GMT | Posted by Ian Chicken

Charles Darwin - Ascension Diary
Naturalist

On the 19th of July we reached Ascension. 
Those who have beheld a volcanic island, situated under an arid climate, will at once be able to picture to themselves the appearance of Ascension. They will imagine smooth conical hills of a bright red colour, with their summits generally truncated,  rising separately out of a level surface of black rugged lava. A principal mound in the centre of the  island, seems the father of the lesser cones. 
It is called Green Hill: its name being taken from the  faintest tinge of that colour, which at this time of the year is barely perceptible from the anchorage. To complete the desolate scene, the black rocks on the coast are lashed by a wild and turbulent sea.

The settlement is near the beach; it consists of several houses and barracks placed irregularly, but well built of white free stone. The only inhabitants are marines, and some negroes liberated from slave-ships, who are paid and victualled by government.  There is not a private person on the island. Many of the marines appeared well contented with their situation; they think it better to serve their one and twenty years on shore, let it be what it may, than in a ship; in this choice, if I were a marine, I should most heartily agree.

The next morning I ascended Green Hill, 2840 feet high, and thence walked across the island to the windward point. A good cart-road leads from the coast-settlement to the houses, gardens, and fields, placed near the summit of the central mountain.  On the roadside there are milestones, and likewise cisterns, where each thirsty passer-by can drink some good water. 
Similar care is displayed in each part of the establishment, and especially in the management of the springs, so that a single drop of water  may not be lost: indeed the whole island may be compared to a huge ship kept in first-rate order.  I could  not help, when admiring the active industry, which had created such effects out of such means, at the same time regretting that it had been wasted on so poor and trifling an end.  M. Lesson has remarked with justice,  that the English nation would have thought of making the island of Ascension a productive spot, any other people would have held it as a mere fortress in the ocean.

Near this coast nothing grows; further inland, an occasional green castor-oil plant, and a few grasshoppers, true friends of the desert, may be met with.  Some grass is scattered over the surface of the central elevated  region, and the whole much resembles the worse parts of the Welsh mountains. But scanty as the pasture appears, about six hundred sheep, many goats, a few cows and horses, all thrive well on it.  Of native animals, land-crabs and rats swarm in numbers. Whether the rat is really indigenous, may well be doubted; there are two varieties as described by Mr. Waterhouse; one is of a black colour, with fine glossy fur, and lives on the grassy summit, the other is brown-coloured and less glossy, with longer hairs, and lives near the settlement on the coast.  Both these varieties are one-third smaller than the common black rat (M. rattus); and they differ from it both in the colour and character of their fur, but in no other essential respect. 
I can hardly doubt that these rats (like the common mouse, which has also run wild) have been imported, and, as at the Galapagos, have varied from the effect of the new conditions to which they have been exposed: hence the variety on the summit of the island differs from that on the coast.  Of native birds there are none; but the guinea-fowl, imported from the Cape de Verde Islands, is abundant, and the common fowl has likewise run wild.  Some cats, which were originally turned out to destroy the rats and mice, have increased, so as to become a great plague.  The island is entirely without trees, in which, and in every other respect, it is very far inferior to St. Helena.

One of my excursions took me towards the S. W. extremity of the island.  The day was clear and hot, and I saw the island, not smiling with beauty, but staring with naked hideousness.  The lava streams are covered with hummocks, and are rugged to a degree which, geologically speaking, is not of easy explanation.  The intervening spaces are concealed with layers of pumice, ashes and volcanic tuff.  Whilst passing this end of the island at sea, I could not imagine what the white patches were with which the whole plain was mottled; I now found that they were seafowl, sleeping in such full confidence, that even in midday a man could walk up and seize hold of them.  These birds were the only living creatures I saw during the whole day.  On the beach a great surf, although the breeze was light, came tumbling over the broken lava rocks.

The geology of this island is in many respects interesting. In several places I noticed volcanic bombs, that is, masses of lava which have been shot through the air whilst fluid, and have consequently assumed a spherical or pear-shape.  Not only their external form, but, in several cases, their internal structure shows in a very curious manner that they have revolved in their aerial course.  The internal structure of one of these bombs, when broken, is represented very accurately in the woodcut.  The central part is coarsely cellular, the cells decreasing in size towards the exterior; where there is a shell-like case about the third of an inch in thickness, of compact stone, which again is overlaid by the outside crust of finely cellular lava.  I think there can be little doubt, first that the external crust cooled rapidly in the state in which we now see it; secondly, that the still fluid lava within, was packed by the centrifugal force, generated by the revolving  of the bomb, against the external cooled crust, and so produced the solid shell of stone; and lastly, that the centrifugal force,  by relieving the pressure in the more central parts of the bomb, allowed the heated vapours to expand their cells, thus forming the coarse cellular mass of the centre.

A hill, formed of the older series of volcanic rocks, and which has been incorrectly considered as the crater of a volcano, is remarkable from its broad, slightly hollowed, and circular summit having been filled up with many successive layers of ashes and fine scoriae.  These saucer-shaped layers crop out on the margin, forming perfect rings of many different colours, giving to the summit a most fantastic appearance; one of these rings is white and broad, and resembles a course round which horses have been exercised; hence the hill has been called the Devil's Riding School.  I brought away specimens of one of the tufaceous layers of a pinkish colour and it is a most extraordinary fact, that Professor Ehrenberg [5] finds it almost wholly composed of matter which has been organized: he detects in it some siliceous shielded fresh-water infusoria, and no less than twenty-five different kinds of the siliceous tissue of plants, chiefly of grasses. 
From the absence of all carbonaceous matter, Professor Ehrenberg believes that these organic bodies have passed through the volcanic fire, and have been erupted in the state in which we now see them.  The appearance of the layers induced me to believe that they had been deposited under water, though from the extreme dryness of the climate I was forced to imagine, that torrents of rain had probably fallen during some great eruption, and that thus a temporary lake had been formed into which the ashes fell.  But it may now be suspected that the lake was not a temporary one.  Anyhow, we may feel sure, that at some former epoch the climate and productions of Ascension were very different from what they now are.  Where on the face of the earth can we find a spot, on which close investigation will not discover signs of that endless cycle of change, to which this earth has been, is, and will be subjected?