CHAP. L] CORAL WELLS. 21 



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 sur- 

 rounding 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 uni- 

 versal 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, uninfluenced alike by rains or 

 drought ; and a steam-engine erected at Potoor, with the 

 intention of irrigating the surrounding lands, failed to 

 lower the water 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 mainly derived by percolation from the sea. 2 



1 For the particulars of this singular salt from sea water by filtration, he 

 well, see Vol. II. Pt. ix. ch. vi. p. 536. suggests that the porous coral rock 



being permeated by salt water, the 

 rain which falls on the surface sinks 

 to the level of the surrounding sea, 

 " and must accumulate there, dis- 

 placing an equal" bulk of sea water 

 and as the portion of the latter in 

 the lower part of the great sponge- 

 like mass rises and falls with the 



2 DAHWIN, 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. Assum- 

 ing it to be impossible to separate 



c 3 



