Never hitherto on this island, so important by its geographical position for ships trading with China, the East Indies, Australia, and New Zealand, have astronomical and magnetic observations and geodesical measurements been so thoroughly ascertained as by the Novara expedition. Upon a carefully measured base-line, various points of the upper and lower margin of the crater were accurately laid down by means of the Theodolite, and the whole island submitted to a geometric network of angles. At the same time the geologist, with the aid of the compass and the patent levels, prepared a chart originally intended for geological purposes only, while the draughtsman of the expedition added to its value, by skilfully sketching in from these given points the configuration of the coast-line of the island. By their united efforts there has been published a chart of St. Paul, which gives even to the minutest details an entirely correct and accurate representation of the form and surface of the island. This minute chart, or plan, was prepared on a scale of 132 Vienna fathoms to one Vienna inch, or 1⁄9504 of the natural size. Moreover, it is intended preparing, from this map and from the various outlines and views taken on the spot, a plastic model of the island after Nature, which, moulded in gypsum, will give scientific inquirers the most accurate conception of its singular structure. Not less interesting for navigators in the Indian Ocean will be the publication of the various observations which, during our stay of 18 days, were made with the barometer, thermometer, tide-gauge, and gauge of the velocity of currents, taken at certain fixed hours, day and night, as also the soundings in the crater-basin, and on both sides of the bar. Although the complete publication of these data must await the appearance of the nautical portion of the present work, we shall give here the most important of these results. The extreme length of the island from N.W. to S.E., is three nautical miles; the superficial area is 1,600,000 Vienna square klafter—1 Vienna klafter = 1 fathom = 6 English feet—100 English square feet = 92 986⁄1000 Vienna square feet. The highest point of the crater-basin is 846 feet; the greatest diameter of the upper rim of the crater is 5490 feet; the least 4590 feet; the greatest diameter of the basin at the level of the sea is 3984 feet, and the least 3444 Vienna feet.
The observations on the state of the weather, taken with much difficulty, are not intended to include the regular observations on the exterior of the island, and in like manner some of those taken in the harbour, or basin of the crater, must be accepted with a certain limitation. For similar reasons, we were unable to fix the rate of the current setting from the sea into the basin, although we secured most extraordinary results considering the circumstances. The amount of specimens of natural history which was procured, was very limited, but on that account was the more valuable. To the geologist, it must be of the very highest interest to find that St. Paul has been classified, with scientific precision, and by dint of personal examination and research, in one of the four main divisions in which, according to the scheme of Alexander Von Humboldt, the volcanic formations of the earth may be divided. Measured by the latest distribution of the volcanic strata by the description of stone found, as laid down by the greatest of German naturalists, St. Paul belongs to the same class as Chimborazo, Popocatepetl, Teneriffe, &c., in a word, to what is known as the Chimborazo formation. A section of the east-side, taken in profile, lays bare its entire geological history, and forms one of the most instructive means of coming to direct conclusions as to its geological structure.
The birth of this island from the bosom of the deep, combined with eruptions of lava and scoriæ, was the last effort of the subterranean forces. Since that period it has been subject wholly and solely to the various terrestrial influences, although the lapse of centuries has not been able to extirpate the last traces of the volcanic fire which once poured forth its currents of molten lava. A large proportion of the level ground is hot, and at the lower edge of the rim of the crater appear several hot springs, the temperature of which, as already remarked, is so high that fish, eggs, potatoes, &c., can be cooked on them in a few minutes. The highest point of St. Paul rises 870 feet above the basin of the crater. Its walls rise abruptly at an angle of about 85°, while the upper surface of the island (with the single exception of a small plateau of about 400 feet on the north side) stretches, at first level from the periphery of the upper margin of the crater, gradually falling away towards the sea-coast, at an angle of about 13°. On its North-west coast, where it is from 100 to 200 feet in perpendicular height, the island presents several small pyramids of pumice, like parasitic warts on the principal mass.
Like the geologist, the botanist also found in this wild spot an unusual opportunity of acquiring accurate information as to the occurrence and propagation of certain kinds of plants in a primitive soil. Six grasses and one reed (cyperaceæ) form the vegetation of the island, one rush and three or four of the grasses forming the majority. The botanist having ascended to the plateau found there two grasses, both of which grew to a certain height only, and at certain places; the one (in the immediate vicinity of the settler's huts,) the oat, or avena; the second a digitaria, in the neighbourhood of the terraced fields, directly opposite the entrance to the crater, in warm positions, which, so soon as the earth is a little disturbed, emit jets of steam. It is still uncertain whether the other kinds of grass, Poa and Setaria Holcus, belong exclusively to St. Paul, or are to be included in the more general group of geographical plants known as that of the islands of Edward's Island, Kerguelen's Island, and St. Paul.
Among the grasses there spring up here and there, but on the whole very sparsely, some wild vegetables which have been planted by previous chance visitors.[69] In the crater there are also Sonchus arvensis and one Plantago (Plantain). On the south margin of the crater are Cerastium (maize-ear chickweed), and Stellaria media (chickweed); both grow on a small piece of ground, and are far from thriving. Of Cryptogamia the botanist found four sorts. Two Parmelias, one Evernia, and one Cladonia, the first-named overrunning the blocks on the edge of the crater with great luxuriance.
[69] Such as Rumex acetosella, Cynara Scolcymus (artichoke); Solanum tuberosum (species of nightshade); Daucus carotta (carrot); Petroselinum sativum (parsley); Brassica oleracea (sea-kail); Raphanus sativus (horse-radish).
Of Algæ there were found 33 species. The stones rolled backwards and forwards by the action of the waves, as also those surfaces which remained covered at lowest tide, were entirely covered with Dicurella flabellata. Most numerous was Gigartina radula, just in a state of fructification. Every movement of the water calls up slender, delicate confervæ, and pale and coloured luminariæ. The breakers have crowned the stones with festoons of the Macrocystis pyrifera. Of Liverworts there were found Marchantia and Jungermania; of foliaceous mosses, Sphagnum (bog-moss), and two kinds of Bruym. Two ferns, just beginning to bear fruit, were found on the plateau, and one Lycopodium (club-moss), which thrives pretty well, and frequently grows on the Sphagnum. On the whole, the botanist of the expedition found on the island, 11 Phanerogamia, 4 Lichens, 33 Algæ, 2 ferns, 2 Liverworts, 3 foliaceous mosses, 1 Lycopodium. In this enumeration are included the European vegetables cultivated by the residents, as also some untended plants, which apparently have been introduced with the vegetables, or have been brought hither by previous visitors. The stony substratum of this island is barely covered with a plastic vegetable substance, which fills the cracks. The walls of the crater, as also the entire plateau, present to view a plain, unrelieved expanse of grass; not, however, like fields clothed with sward, but single tufts pressing one upon the other, which seem like the grave-mounds of a hundred bygone generations of plants. Frequently, at the foot of a block of pumice, all overrun with grasses of all sorts, one comes upon a moss or a stem of fern on one of the pieces of lava that has been washed up, or perceives with amazement in some out-of-the-way place, and utterly neglected, good old acquaintances from Europe, such as carrots, parsley, potatoes, &c., which apparently have been begun to be cultivated on some of the terraces, whence they have propagated themselves in a wild state all over the island. But not a tree, or bush, is to be met with throughout the island.
In like manner, although the zoologist seemed to have but a poor prospect at St. Paul, it presented materials for most satisfactory speculation to the attentive naturalist. Only one of the grasses is infested by an insect, which appears in great numbers, a very tiny cicada (cricket), the Delphis hemiptera, of which, according to the zoologist of the expedition, it is hard to say whether it became indigenous to St. Paul before, or contemporaneous with the arrival of man. Among other insects that have certainly been introduced here, the zoologist found the common bluebottle-fly, a gnat, the universally found cockroach, the book-tick (acarus eruditus), one kind of earwig, and the flea; besides the Isopodis, our common barrel-worm,[70] in almost fabulous quantities. These animals invariably follow man wherever he plants his foot, living upon garbage or decaying organic matter. With the exception of the clothes-moth, which has probably been introduced among the wool-stuffs, there are in the island no butterflies, none of the been tribe, no Neuroptera. Mites also need scarcely be reckoned, since the only representative, the common cheese-mite, is more apt to become extinct than to thrive; on the other hand, there are two kinds of spiders, for which the enormous number of flies furnish sufficient food.
[70] These loathsome animals cover the island in such quantities that one of the naturalists reckoned them at 6,000,000,000, counting 100 as the minimum to each square foot of the island.
The species belonging to the sea are somewhat more plentifully represented, although, with few exceptions, very small and insignificant. The largest shell fish, a Tritonium, only attains a length of 3 inches; Patella, which is very plentiful all round the island, is only 1 inch long; several sorts of snails (such as Buccinum, Defrancia, Mangelia, Paludinella, Adeorbis, Janthina, Fissurella, Scutellina, Lepidopleurus, Bulla, Asteronotus, Doto), are barely a few lines in length, or even less.