Cruise of the 'Alert'. R. W. Coppinger

Чтение книги онлайн.

СКАЧАТЬ were few. However, we succeeded in capturing many specimens of living Foraminifers (mostly of the genus Orbitolites), stalk-eyed Crustaceans, Radiolarians, an Ianthina, a few Salpæ, and the pretty little Pteropod Mollusc, the Criseis aciculata, besides many other organisms which the rapid motion of the net through the water had rendered unrecognizable. As it is usually found that these minute pelagic organisms are to be obtained from the surface in most abundance at night-time, and during the day retreat for some fathoms from the glare of the sunlight, I constructed a wooden apparatus on the principle of a kite, which I attached to the towing line at some three or four yards from the net, and which had the effect of dragging down the net some yards below the surface, and then retaining it at a uniform depth. It of course required to be adjusted each time to suit the required depth and the rate of the vessel, but it had this great advantage over the usual system of employing heavy weights, that the strain not being nearly so great, a light and manageable rope could be used; and that, moreover, the adjustment for depth could be readily made by altering the trim of this water-kite. When I first tried this apparatus, and before I had succeeded in trimming it satisfactorily, it caused great amusement to the bluejackets by the playful manner in which it manœuvred under our stern, now diving deeply towards our rudder post (the shimmer of the white wood in the deep blue water reminding one of a dolphin), and now whimsically rising rapidly to the surface with an impetus that shot it fully six feet out of the water.

      On the 4th of October, the captain made some experiments with the "Lucas deep-sea sounder." It consists of a strong brass drum carrying 2,000 fathoms of fine steel wire, and fitted with a cyclometer which registers on a dial the number of fathoms of wire run out. The sinker, which weighs 20 lbs., is made of lead, and has at its lower extremity a bull-dog snapper, which, on striking the ground, shuts up suddenly, so as to enclose a sample of the sea bottom. The apparatus is supposed to be capable of sounding to a depth of 500 fathoms in a vessel going 5 knots, and to 50 fathoms when going 12 knots. It is said to be a modification of an invention of Sir W. Thompson's. We subsequently used this largely, and found it to be a most convenient and expeditious method of sounding to depths of 500 fathoms, with the ship almost stationary. The wire could be wound up again while the ship was under way.

      During the forenoon of this same day we saw, to our astonishment, a land swallow, which flew about the ship for a few minutes, and then went on his way rejoicing. He would have had to travel 254 miles to make the nearest land, which was the island of Porto Santo.

      An erratic fragment of gulfweed (Sargassum bacciferum) was entangled in the tow-net on the 5th of October, when we were 105 miles north-east of Madeira, a circumstance which is of interest as regards the distribution of the plant, the locality cited being considerably beyond the northern limit of the great eddy between the Gulf Stream and the Atlantic equatorial current, commonly called the Sargasso Sea. It was encrusted with a delicate white Polyzoon (Membranipora), and among other organisms carried on its fronds a pretty little Spirorbis shell, and several entomostracous Crustaceans of a deep-blue colour.

      The phosphorescence of the sea is a trite subject, and one about which a very great deal has been written; but nevertheless, of its actual cause, or of the purposes which it is intended to serve, really very little is positively known. The animals to which it would seem mainly due are the small stalk-eyed Crustacea, the Pyrocystis noctiluca, and the Tunicate Molluscs. I have sometimes observed, when occupied at night in sifting the contents of a tow-net, that these organisms, as they were being sucked through the nozzle of the dip-tube, emitted flashes of light, so brilliant, that they could be distinctly seen even in a well-lighted room. During the voyage from England to Madeira, the wake of the ship was every night, with one exception, phosphorescent. The exception alluded to was on the night previous to our arrival at Madeira, when probably the unusual brilliancy of the moonlight caused the light-emitting creatures to retreat a few yards from the surface, as happens in the day-time. I have often noticed that while the phosphorescence of the comparatively still water abeam of the ship and on her quarter usually seems to emanate from large spherical masses of about a foot in diameter (commonly called "globes of fire"), yet the luminosity of the broken water in the vessel's immediate wake comes apparently from innumerable minute points. I have rarely captured any of the larger jellyfishes in the tow-net; and on those nights when I have observed the water lighted up the most brilliantly, the prevailing organisms have proved to be the small entomostracous Crustaceans.

      The morning of the 7th of October broke cool and hazy, as we steamed up and dropped anchor in Funchal Roads, on the south side of the island of Madeira. Crowds of native boats, with their half-naked occupants, quickly thronged around; remaining, however, at a respectful distance, until the boat containing the haughty pratique officer came alongside. On the present occasion this portentous individual was contented with a very superficial inquiry into our sanitary condition, and after a few formal questions as to our tonnage, complement of crew, number of guns, and general condition, shoved off with the laconic exclamation, "All right!" We soon availed ourselves of this permission to visit the shore.

      The most conspicuous objects in Funchal, as seen from the anchorage, are the "Loo Rock" (used as a fort and lighthouse), on the west side of the town, and on the centre of the crescent-shaped beach which fronts the town a remarkable and lofty cylindrical tower of dark-brown stone. This tower, we were informed, was built about the year 1800, and was intended as a support for a huge crane, which was to facilitate the loading and disembarkation of the cargo of merchant ships. The tower as it stands is about eighty feet in height, and as its base is now about forty yards distant from high-water mark on the beach, as an article of utility it is quite effete. Our surveyors have ascertained that the land has not been elevated since the first admiralty surveys. This they arrive at by a comparison of old and recent charts with known marks on the shore, and we are therefore inclined to believe that the beach has been silted up by accumulations of basaltic rubble brought down by the two adjoining rivers, and here washed inshore by the sea. The tower is now without any appearance of the crane, and raises its plain cylindrical body in gloomy grandeur, reminding one of the old round towers of Ireland; and, as in their case, its origin will probably some years hence be veiled in obscurity.

      Madeira was considered to be looking unusually dingy, on account of a long season of drought, rain not having fallen for nine months. But some two or three days after our arrival a great religious ceremony took place at the village of Machico, eight miles to the eastward of Funchal. The object was to offer up prayers for rain; and, sure enough, two days afterwards, rain fell abundantly!

      

      During our stay here the dredge was several times brought into requisition. On the 8th of October, a party, consisting of the captain, Lieut. Vereker, some seamen, and myself, started in the steam-cutter on a dredging expedition to the bay of Santa Cruz, which is distant about eight miles from Funchal. As we steamed along the coast, we had excellent opportunities of observing the sections exhibited by the cliffs of the varieties of volcanic rock of which the upper crust of the island is mainly formed. At Point Garajas (Brazen Head), of which Lieut. Vereker made a good sketch, the north-east face of the cliff presents a magnificent dyke—a nearly vertical seam of dark lava, about three feet in width and two hundred feet in height, extending from summit to water line, and sealing up this long fissure in the older trachytic rock of the head. Farther on, masses of basalt resting unconformably on variously arranged layers of laterite tuff and trachyte, the latter in many places honeycombed in weird fantastic caverns, afforded a fertile subject for geological reveries into the early history of this now beautiful island. On reaching the bay of Santa Cruz, we lowered the dredge in thirty-five fathoms, finding, as we had half anticipated, that it was altogether too heavy to ride on the mass of sand that here forms the sea bottom. It buried itself like an anchor, and it was not without great difficulty that we could succeed in dislodging it. On bringing it up, we found it to contain some shells of the genera Cardium, Pecten, Cypræa, Oliva, and Dentalium, a few small Echini, a Sertularian Polyp, several Annelids—among others, a Nereis—and Alcyonarians. We returned on board soon after dusk, having spent a most enjoyable, if not materially profitable, day. On subsequently dredging in СКАЧАТЬ