The sand, which covers a vast extent of the peninsula of Jaffna, and in which the coco-nut and Palmyra-palm grow freely, has been carried by the currents from the coast of India, and either flung upon the northern beach in the winter months, or driven into the lake during the south-west monsoon, and thence washed on shore by the ripple, and distributed by the wind.

The arable soil of Jaffna is generally of a deep red colour, from the admixture of iron, and, being largely composed of lime from the comminuted coral, it is susceptible of the highest cultivation, and produces crops of great luxuriance.  This tillage is carried on exclusively by irrigation from innumerable wells, into which the water rises fresh through the madrepore and sand; there being no streams in the district, unless those percolations can be so called which make their way underground, and rise through the sands on the margin of the sea at low water.

Wells in the Coral Rock.—­These phenomena occur at Jaffna, in consequence of the rocks being magnesian limestone and coral, overlying a bed of sand, and in some places, where the soil is light, the surface of the ground is a hollow arch, so that it 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 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]