CHAP. I.] 



COEAL WELLS. 



23 



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 

 hills, is clothed with perennial foliage; and even the 

 sand-drifts, to the ripple on the sea line, are carpeted 



fall of rain is less than in England, 

 being but thirty-inches ; whilst the 

 average heat is the highest in Ceylon, 

 and the evaporation great in pro- 

 portion. Throughout the peninsula, 

 I am informed by Mr. Byrne, the 

 Government surveyor of the dis- 

 trict, 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 No- 

 vember 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 re- 

 mains 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 filtra- 

 tion, renders its fluctuations imper- 

 ceptible. 



On the other hand, the well of 

 Potoor, the phenomena of which in- 

 dicate its direct connection with the 

 sea, by means of a fissure or a channel 

 beneath an arch of magnesian lime- 

 stone, rises and falls a few inches in 

 the course of every twelve hours. 

 At Navokeiry, a short distance from 

 Potoor, another well does the same, 

 whilst the well at Tillipalli is en- 

 tirely 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 lieayle, 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 afterwards 

 propounded by Darwin of the re- 

 tention of the river-water, which he 

 says, "doesnotmix with the saltwater 

 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 luith its contents 

 far 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 ex- 

 periment 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 intermix- 

 ture admitted by Admiral Fitzroy, 

 must by reiterated occurrence tend in 

 time to taint the fresh water which is 

 affected by the movement. An analo- 

 gous fact is demonstrable by the test of 

 the sponge ; for I find that on charging 

 one with coloured fluid, and immers- 

 ing it in a vessel containing water 

 perfectly pure, little or no intermix- 

 ture takes place so long as the pure 

 water is undisturbed ; but on causing 

 an artificial tide, by gradually with- 

 drawing and as gradually replacing a 

 portion of the surrounding contents 

 of the basin, the tinted water in the 

 sponge becomes displaced and dis- 

 turbed, 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. 



c 4 



