in some places, where the soil is light, the surface of the ground is a hollow arch, which resounds as if a horse's weight were sufficient to crush it inwards. This is strikingly perceptible in the vicinity of the remarkable well at Potoor1, on the west side of the road leading from Jaffna to Point Pedro, where the surface of the surrounding country is only about fifteen feet above the sea-level. The well, however, is upwards of 140 feet in depth; the water fresh at the surface, brackish lower down, and intensely salt below. According to the universal belief of the inhabitants, it is an underground pool, which communicates with the sea by a subterranean channel bubbling out on the shore near Kangesentorre, about seven miles to the north-west. A similar subterranean stream is said to conduct to the sea from another singular well near Tillipalli, in sinking which the workmen, at the depth of fourteen feet, came to the ubiquitous coral, the crust of which gave way, and showed a cavern below containing the water they were in search of, with a depth of more than thirty-three feet. It is remarkable that the well at Tillipalli preserves its depth at all seasons alike, uninfluenced by rains or drought; and a steam-engine erected at Potoor, with the intention of irrigating the surrounding lands, failed to lower it in any perceptible degree. Other wells, especially some near the coast, maintain their level with such uniformity as to be inexhaustible at any season, even after a succession of years of drought a fact from which it may fairly be inferred that their supply is chiefly derived by percolation from the sea.2 1 For the particulars of this singular well, see the Chap. on Jaffna, Vol. II. 2 DARWIN, in his admirable account of the coral productions of the Pacific and Indian oceans, has propounded a theory as to the abundance of fresh water in the atolls and islands on coral reefs, furnished by wells which ebb and flow with the tides. Assuming it to be impossible to separate salt from sea water by filtration, he suggests that the porous coral rock An idea of the general aspect of Ceylon will be formed from what has here been described. Nearly four parts of the island are undulating plains, slightly diversified being permeated by salt water, the rain which falls on the surface must sink to the level of the surrounding sea, "and must accumulate there, displacing an equal bulk of sea water -and as the portion of the latter in the lower part of the great spongelike mass rises and falls with the tides, so will the fresh water near the surface."- Naturalist's Journal, ch. XX. But subsequent experiments have demonstrated that the idea of separating the salt by filtration is not altogether imaginary, as Darwin seems to have then supposed, and Mr. WITT, in a remarkable paper On a peculiar power possessed by Porous Media of removing matters from solution in water, has since succeeded in showing that "water containing considerable quantities of saline matter in solution may, by merely percolating through great masses of porous strata during long periods, be gradually deprived of its salts to such an extent as probably to render even sea-water fresh."-Philos. Mag., 1856. Divesting the subject therefore of this difficulty, other doubts would appear to suggest themselves as to the applicability of Darwin's theory to coral formations in general. For instance, it might be supposed that rain falling on a substance already saturated with moisture, would flow off instead of sinking into it; and that being of less specific gravity than salt water, it would fail to "displace an equal bulk" of the latter. There are some extraordinary but well attested statements of a thin layer of fresh water being found on the surface of the sea, after heavy rains in the Bay of Bengal. (Journ. Asiat. Soc. Beng. vol. v. p. 239.) Besides, I fancy that in the majority of atolls and coral islands the quantity of rain which so small an area is calculated to intercept would be insufficient of itself to account for the extraordinary abundance of fresh water daily drawn from the wells. For instance, the superficial extent of each of the Laccadives is but two or three square miles, the surface soil resting on a crust of coral, beneath which is a stratum of sand; and yet on reaching the latter, fresh water flows in such profusion, that wells and large tanks for soaking cocoa-nut fibre are formed in any place by merely "breaking through the crust and taking out the sand.' Madras Journal, vol. xiv. It is curious that the abundant supply of water in these wells should have attracted the attention of the early navigators, and Cosmas Indicopleustes, writing in the sixth century, speaks of the numerous small islands off the coast of Taprobane, with abundance of fresh water and coconut palms, although these islands rest on a bed of sand. (Cosmas Ind. ed. Thevenot, vol. i. p. 3, 20.) It is remarkable that in the little island of Ramisseram, one of the chain which connects Adam's Bridge with the Indian continent, fresh water is found freely on sinking for it in the sand. But this is not the case in the adjacent island of Manaar, which participates in the geologic character of the interior of Ceylon. The fresh water in these wells always fluctuates with the rise and fall of the tides. In some rare instances, as on the little island of Bitra, which is the smallest inhabited spot in the Laccadives, the water, though abundant, is brackish, but this is susceptible of an explanation quite consistent with the experiments of Mr. Witt, which require that the process of percolation shall be continued "during long periods and through great masses of porous strata;" Darwin equally concedes that to keep the rain fresh when banked in, as he assumes, by the sea, the mass of madrepore must be "sufficiently thick to prevent mechanical admixture; and where the land consists of loose blocks of by offsets from the mountain system which entirely covers the remaining fifth. Every district, from the depths of the valleys to the summits of the highest coral with open interstices, the water, if a well be dug, is brackish." Conditions analogous to all these particularised, present themselves at Jaffna, and seem to indicate that the extent to which fresh water is found there, is directly connected with percolation from the sea. The quantity of rain which annually falls is less than in England, being but thirty inches, whilst the average heat is highest in Ceylon, and the evaporation great in proportion. Throughout the peninsula, I am informed by Mr. Byrne, the Government surveyor of the district, that as a general rule "all the wells are below the sea level." It would be useless to sink them in the higher ground, where they could only catch surface water. The November rains fill them at once to the brim, but the water quickly subsides as the season becomes dry, and "sinks to the uniform level, at which it remains fixed for the next nine or ten months, unless when slightly affected by showers." "No well below the sea level becomes dry of itself," even in seasons of extreme and continued drought. But the contents do not vary with the tides, the rise of which is so trifling that the distance from the ocean, and the slowness of filtration, renders its fluctuations imperceptible. On the other hand the well of Potoor, the phenomena of which indicate its direct connection with the sea, by means of a fissure or a channel beneath the arch of magnesian limestone, rises and falls a few inches in the course of every twelve hours. Another well at Navokeiry, a short distance from it, does the same, whilst the well at Tillipally is entirely unaffected as to its level by any rains, and exhibits no alteration of its depths on either monsoon. ADMIRAL FITZROY, in his Narrative of the Surveying Voyages of the Adventure and Beagle, the expedition to which Mr. Darwin was attached, adverts to the phenomenon in connection with the fresh water found in the Coral Islands, and the rise and fall of the wells, and the flow and ebb of the tide. He advances the theory propounded by Darwin of the retention of the river-water, which he says, "does not mix with the salt water which surrounds it except at the edges of the land. The flowing tide pushes on every side, the mixed soil being very porous, and causes the water to rise: when the tide falls, the fresh water sinks also. A sponge full of fresh water placed gently in a basin of salt water, will not part with its contents for a length of time if left untouched, and the water in the middle of the sponge will be found untainted by salt for many days: perhaps much longer if tried."-Vol. i. p. 365. In a perfectly motionless medium the experiment of the sponge may no doubt be successful to the extent mentioned by Admiral Fitzroy; and so the rain-water imbibed by a coral rock might for a length of time remain fresh where it came into no contact with the salt. But the disturbance caused by the tides, and the partial intermixture admitted by Admiral Fitzroy, must by reiterated occurrence tend in time to taint the fresh water which is affected by the movement: and this is demonstrable even by the test of the sponge; for I find that on charging one with coloured fluid, and immersing it in a vessel containing water perfectly pure, no intermixture takes place so long as the pure water is undisturbed; but on causing an artificial tide, by gradually withdrawing and as gradually replacing a portion of the surrounding contents of the basin, the tinted water in the sponge becomes displaced and disturbed, and in the course of a few ebbs and flows its escape is made manifest by the quantity of colour which it imparts to the surrounding fluid. hills, is clothed with perennial foliage; and even the sand-drifts, to the ripple on the sea line, are carpeted with verdure, and sheltered from the sunbeams by the cool shadows of the palm groves. SOIL.But the soil, notwithstanding this wonderful display of spontaneous vegetation, is not responsive to systematic cultivation, and is but imperfectly adapted for maturing a constant succession of seeds and cereal productions. Hence arose the disappointment which beset the earliest adventurers who opened plantations of coffee in the hills, on discovering that after the first rapid development of the plants, delicacy and languor ensued, which were only to be corrected by returning to the earth, in the form of manures, those elements with which it had originally been but sparingly supplied, and which were soon exhausted by the first experiments in cultivation. Patenas. The only spots hitherto found suitable for planting coffee, are those covered by the ancient forests of the mountain zone; and one of the most remarkable phenomena in the œconomic history of the island, is the fact that the grass land on the same hills, closely adjoining the forests and separated from them by no visible line save the growth of the trees, although they seem to be identical in the nature of the soil, have hitherto proved to be utterly insusceptible of reclamation or culture by the coffee-planter. These verdant openings, to which the natives have given the name of patenas, generally occur about the middle elevation of the hills, the summits and the hollows being covered with the customary growth of timber trees, which also fringe the edges of the mountain streams that trickle down these park-like openings. The forest approaches boldly to the very edge of a "patena," not disappearing gradually or sinking into a growth of underwood, but 1 See a paper in the Journal of on Tropical Cultivation and its Limits, Agriculture, for March, 1857, Edin.: | by DR. MACVICAR. stopping abruptly and at once, the tallest trees forming a fence around the avoided spot, as if they enclosed an area of solid stone. These sunny expanses vary in width from a few yards to many thousands of acres ; in the lower ranges of the hills they are covered with tall lemon-grass (Andropogon schonanthus), whose oppressive perfume and coarse texture, when full grown, render it distasteful to cattle, which will only crop the delicate braird that springs after the surface has been annually burnt by the Kandyans. Two stunted trees, alone, are seen to thrive in these extraordinary prairies, Careya arborea, and Emblica officinalis, and these only below an altitude of 4000 feet; above this, the lemongrass is superseded by harder and more wiry species; but the earth is still the same, a mixture of decomposed quartz largely impregnated with oxide of iron, but wanting the phosphates and other salts which are essential to highly organised vegetation.1 The extent of the patena land is enormous in Ceylon, amounting to millions of acres; and it is to be hoped that the complaints which have hitherto been made by the experimental cultivators of coffee in the Kandyan provinces may hereafter prove exaggerated, and that much that has been attributed to the poverty of the soil may eventually be traced to deficiency of skill on the part of the early planters. The natives in the same lofty localities find no deficient returns in the crops of rice, which they raise in the ravines and hollows, into which the earth from above has been washed by the periodical rains; but the cultivation of rice is so entirely dependent on the 1 HUMBOLDT is disposed to ascribe the absence of trees in the vast grassy plains of South America, to "the destructive custom of setting fire to the woods, when the natives want to convert the soil into pasture: when during the lapse of centuries grasses and plants have covered the surface with a carpet, the seeds of trees can no longer germinate and fix themselves in the earth, although birds and winds carry them continually from the distant forests into the Savannahs."- Narrative, vol. i. ch. vi. p. 242. |