Chap. I.] 



COKAL 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 

 hiUs, is clothed "wdth perennial fohage ; and even the 

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



of rain wliicla anniially falls is less 

 than in Enjiiand, being but thii-ty 

 inches ; whilst the average heat is 

 highest in Ceylon, and the evaporation 

 great in proportion. Throughout the 

 peninsula, I am informed by Mr. 

 BjTne, the Government surveyor of 

 the district, that as a general rule 

 " all the uvlls are helow the sea level." 

 It would be useless to sink them in 

 the higher ground, where they could 

 only catch surfece water. The No- 

 vember rains fill them at once to the 

 brim, but the water quickly subsides 

 as the season becomes dry, and " sinJin 

 to the toiifonn level, at which it re- 

 mains fixed for the next nine or ten 

 months, imless when slightly affected 

 by showers." '' No well heloxo the sea 

 level becomes dry of itself," even in 

 seasons of extreme and continued 

 drought. But the contents do not 

 vaiy 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 the arch of magiiesian lime- 

 stone, rises and falls a few inches in 

 the com'se of every twelve hours. 

 Another well at Xavokeiry, a short 

 distancefrom it, does the same, whilst 

 the well at Tillipalli is entirely im- 

 affected as to its level by any rains, 

 and exhibits no alteration of its 

 depths on either monsoon. Admiral 

 FiTZROT, in his Narrative of the 

 Survei/inf/ Voyayes of the Adventure 

 and Beayle, the expedition to which 

 IMi*. Darwin was attached, adverts to 

 the phenomenon in connection with 

 the fresh water foimd in the Coral 

 Islands, and the rise and fiill of the 



wells, and the flow and ebb of the 

 tide. lie advances the theory pro- 

 poimded by Dai-win of the retention 

 of the river-water, which he says, 

 " does not mix with the salt water 

 which sm-romids 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 : 

 wlien the tide falls, the fresh water 

 sinks also. A sponge fall of fresh 

 water placed gently in a basin of salt 

 water, ivill not jnirt 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 miich 

 longer if tried." — -Vol. i. p. 365. In 

 a perfectly motionless medium the 

 experiment of the sponge may no 

 doubt be successfiU to the extent 

 mentioned by Admiral Fitzroy ; and 

 so the rain-water imbibed by a coral 

 rock might for a length of time re- 

 main fresh where it came into no 

 contact with the salt. But the dis- 

 turbance caused by the tides, and 

 the partial intermixture admitted by 

 Admiral Fitzroy, must by reiterated 

 occm-rence tend in time to taint the 

 fresh water which is affected by the 

 movement : and this is demonstrable 

 e-\en hy the test of the sponge ; for I 

 find that on charging one with coloured 

 fluid, and immersing it in a vessel con- 

 taining water perfectly pure, no inter- 

 mixture 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 siu-rounding 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 

 impai'ts to the surrounding fluid. 



c 4 



