July, 1911.] 



68 



Miscellaneous. 



turist, and an endeavour will be made 

 to treat the subject in a popular way. 

 Now the bare rock or the purely sandy 

 soil have not much in them to interest 

 the agriculturist at first sight. He can- 

 not grow crops on either, and he cares 

 for nothing else. All the same, both 

 these uninteresting looking objects may 

 come in useful. 



o. The function of a well is to supply 

 water, and the suggestion which brought 

 forth this paper was, it is believed, not 

 wholly unconnected with the subject of 

 " School Gardens," one which is dear to 

 the heart of the Society's Secretary. 

 The well is an important item in the 

 school garden (or any other garden), 

 and is required both for the suppiy of 

 water to quench the thirst of the 

 scholar when he has worked as hard as 

 he is expected to work, and also that of 

 the various plants which are grown. 

 The quality of the water is important 

 in the former case, and it may be briefly 

 suggested that, all other things being 

 equal, the site of any well, the water 

 from which is to be used later on for 

 dietetic purposes, should be selected, so 

 that the natural surface drainage of 

 the ground falls away in every direction, 

 if possible, from the well, and in the 

 case of, say, a house or school compound, 

 the safest position for the well, having 

 regard only to the question of quality 

 in the water, will be found in the highest 

 point of the ground. Manifestly in the 

 ease of sidelong ground the possibility 

 or probability of contamination from 

 the neighbouring higher ground must 

 also be considered. This point seems 

 almost too obvious to require notice, but 

 the writer has seen many wells in pri- 

 vate and public places so situated as to 

 lead one to suppose that the main object 

 in the original selection of the site had 

 been to secure the maximum of pollu- 

 tion in the water, 



7. The water which reaches the 

 ground surface in the form of rain, 

 assuming that the surface has a slope, 

 will, in the case of bare rock, run down 

 the slope until it meets a place where 

 the rock has some " overlay " — more or 

 less deep according to circumstances — 

 of earth or soil. The latter may take 

 the form of stiff and partly watertight 

 clay, and in such a case the water can- 

 not easily percolate into the soil, and 

 tends to travel further on or near the 

 surface. Such places are easily recog- 

 nized, as the ground near the bare rock 

 margin is always unduly wet after rains. 

 To sink a well in such a position would 

 be a mistake, as the probability is, the 

 subsoil would be found relatively dry 



and waterless, possibly even at a depth 

 approaching that of the, rock surface. 



It is not, however, very likely that 

 such retentive clay would be found in 

 this position, especially if the rock 

 surface is steep, as the latter has nearly 

 always undergone a process of partial 

 disintegration, and the detritus so pro- 

 duced takes the form of gravelly or 

 sandy soil, which quickly absorbs the 

 water running off the rock surface. 



All underground water has a ten- 

 dency to travel to a place where it can 

 repose at a lower level, and does travel 

 to a greater or less extent due to the 

 force of gravity. This travel of the 

 water is arrested in various ways and 

 in varving degrees. It may, in its 

 underground progress, meet a bar of 

 l-ock or watertight clay which it cannot 

 pass, and then it must accumulate at 

 this barrier until either its motion is 

 entirely arrested, or until it flows again 

 over the top of this underground dam, 

 as it may be called, and finds its way to 

 lower levels. In either case a sort of 

 underground reservoir is formed, and if 

 the depth below the surface be not too 

 great, such a position is favourable for a 

 well site. (See Diagram No. 1.) 



In the case of the water flowing off 

 bare rock, as described above, and sink- 

 ing under the surface (at the rock 

 margin) into a gravelly soil, it will con- 

 tinue to travel underground until it 

 meets a clay or rock bar such as that 

 described, and the former is very fre- 

 quently found at the place where the 

 ground surface flattens out into a plain 

 or more gently sloping surface below 

 some mountain or rock hill. 



Rather a good instance of this is found 

 in the case of Kurunegala rock (Diagram 

 No. 2 shows the idea). The water which 

 has been collected on its surface appears 

 again on the surface of the ground 

 lower down — but in this ease relatively 

 close by — in the form of springs, of 

 which the " Rajapihilla " is perhaps the 

 best known. There are, however, many 

 others more or less well defined. There 

 is evidently some watertight bar of rock 

 or clay near the position of these springs 

 which compels the water in its travel to 

 reach the ground surface again. In 

 most similar positions the probability 

 is that the same phenomena would be 

 found, and it would not be difficult to 

 select a good site for a well. 



8. Though not necessarily always 

 true, it is still very often found that the 

 ground, having regard to its surface 

 and slopes, is imitated by the subsoil 

 strata, that is to say, the planes ot the 

 surfaces of the latter are [.often found to 



