July, 1911.] 



67 



Miscellaneous. 



ground surface in a bore hole. It will 

 only rise to a level approximating to 

 that of the lowest point in the outcrop, 

 and a water supply so obtained is only of 

 practical value in extraordinarily dry 

 countries such as parts of Australia. 

 When the water has reached its maxi- 

 mum level in the bore, it may still lie 

 hundreds of feet below the ground sur- 

 face, and has to be raised by artificial 

 means, such as "deep-well" pumps, which 

 are generally costly to instal and operate. 

 In the cases where one side only of the 

 outcrop is depressed and the other side 

 lies at a considerable elevation an 

 artesian well may be possible and 

 effective, delivering water with more or 

 less pressure at the ground surface, but 

 in such cases, speaking generally, the 

 higher side of the outcrop must be 

 relatively high compared to the position 

 of the bore hole and also comparatively 

 close. The water supply (by rainfall or 

 otherwise) at the position of the upper 

 outcrop must be abundant. 



The occurrence of springs on the sur- 

 face as described earlier in this paper is 

 a condition which partly partakes of 

 the nature of an artesian system. 

 Sufficient has been said to indicate the 

 general conditions, which are subject to 

 innumerable modifications, and also to 

 point to the fact an artesian system in 

 such a position as, say, a small island or 

 a promontory.is a practical impossibility, 

 except on a very small scale, and then 

 only in the region of high hills or 

 mountains. 



12. These notes, written as they are 

 for the Ceylon Agricultural Society, 

 would hardly be complete without a 

 brief reference to the very remarkable — 

 probably unique— conditions which pre- 

 vail in tne Jaffna peninsula, and are all 

 the more appropriate, as referring to 

 the district where intense cultivation 

 is the order of the day, and where wells 

 are to be found every few yards, though 

 generally sunk and lined at very con- 

 siderable expense to the landowners. 



The following particulars about the 

 " natural " wells— so called— will be inr 

 teresting to those who are not already 

 acquainted with them :— 



There are three of these " natural" 

 wells— possibly more— which are well 

 known in Jaffna : the " Nilaverei " or 

 Puttur well, the " Yama " well at Urelu, 

 and the " Devil's well " (" Pe-kinarn ") at 

 Kurumbakattu. A description of the 

 first will be sufficient, as they are all 

 similar in natural formation. 



The Puttur well resembles a small 

 " keni," or bathing tank, such as is 

 generally found at the temples. It is 

 48 feet long by 36 feet wide, with the 



usual ramped slope at one side leading 

 down to the water. 



The writer is unaware what the 

 actual circumstances were attending 

 the cutting of this well, but judging by 

 appearances it would seem that those 

 who were engaged on the work intended 

 excavating the usual "keni" and finish- 

 ing up with perhaps 3 feet deep of 

 water. They would appear to have 

 been unaware how " thin the ice " was — 

 in this case the rock crust — and it can 

 only be conjectured that this crust 

 broke through and part or the whole of 

 the bottom fell in ! One is compelled to 

 this belief, as otherwise it would have 

 been difficult to get any men to under- 

 take such dangerous work. 



At all events the result is certain. 

 This crust representing a thickness in 

 all of, say, 14 feet, that is 9 feet of rock 

 and 5 feet of clay overlay, was broken 

 through and stood over a cavity filled 

 with water, but of what dimensions 

 nobody as yet knows. The total depth 

 of water was measured by the writer, 

 and amounts to 147 feet 6 inches, of 

 which the top 80 feet or so is fresh water 

 and the remainder salt. 



The level of the water surface is 

 practically invariable (only rising after 

 heavy rains), and represents, of course, 

 the ground water plane, which at this 

 place and in dry weather stands at 

 almost exactly 2 feet ever mean sea 

 level. 



There are only a few inches difference 

 between the levels of the water planes 

 in the three " natural " wells mentioned 

 above, and they are relatively almost 

 exactly in proportion to the distances 

 respectively of these wells from the sea 

 at the nearest point, the greatest dis- 

 tance representing the highest level. 

 It would appear therefore that the 

 water plane is represented by a very 

 flat cone with its apex at the most 

 central point of this portion of the 

 peninsula. It may also be taken as 

 exceedingly probable that the margin 

 between the salt and fresh water— at 

 what may be called the " salt water 

 plane" — takes the form of an inverted 

 cone, with its apex situated at the same 

 point and its base coinciding with the 

 mean sea plane all round Che coast. 

 (Diagram No. 6 shows this.) 



The formation is all limestone rock, 

 Avhich is perforated in a most remark- 

 able way with holes and cavities of all 

 sizes, and these represent the under- 

 ground storage space. Investigations 

 some years ago in connection with the 

 proposed Jaffna water supply showed 

 that these conditions were uniform all 

 over the north end of the peninsula, and 



