This is strikingly perceptible in the vicinity of the remarkable well at Potoor[1], 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.
[Footnote 1: For the particulars of this singular well, see Vol.II.

Pt.
IX.ch.vi.p.

536.] 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.[1] [Footnote 1: DARWIN, in his admirable account of the coral formations 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.