la 



an iDtermitteDt stream, sometimes a Braall stream, 

 sometimes a river. It is by journeying' by road 

 over the plateau by cycle or otherwise, instead of 

 keeping* to the valleys and cutting through the 

 hills by train, that wh get an iuimense advantage 

 in studying the excavating work of nature. 



To study the nature of strata in our district, we 

 cannot do better than take advantage of the 

 natural section cut through the North Downs by 

 our river Stour. It will be seen that chalk is the 

 chief material which concerns us with these nail- 

 bournes, and it is necessary to look into the nature 

 of a great mass of chalk to observe the part it 

 plays in the perpetual circulation of water. 



Of all the rain that falls upon the earth, it is 

 calculated that not more than one-third runs oS 

 the surface and enters the sea by rivers, and in a 

 cbalk district litce this, I believe it to be even less. 

 One might well wonder what becomes of the rest. 

 Part of it we know is evaporated, part of it feeds 

 animal and vegetable life, but there remains an 

 ample supply to enter the earth. The soil absorbs 

 water, and allows it to sink down into the subsoil ; 

 beneath the subsoil water meets with the material 

 which composes the top stratum, which i? in this 

 case cbalk, and, according to the nature of this 

 stratum, by its absorbent powers or by innumerable 

 crevices and fisbures, down such natural channels 

 the water passes. We are well aware of the 

 absorbent properiies of chalk. A practical way of 

 testing it is to lay a small piece on one's tongup, 

 but to put it to a further test it is found that 

 chalk will take up half its own bulk of water, and 

 yet hardly appear wet, or a cubic foot of soft chalk 

 'will hold as much as two gallons of water in bulk. 

 Chalk behaves much like a sponge, the water 

 tending to sink to the bottom. Cbalk parts with 

 its water fairly easily, for by exhaustive pumping 

 large quantities of water are obtained, yet there is 

 a friction as well as the capillary attraction, 

 which prevents water freely passing from one 

 part to another, or readily finding its level. Then 

 we have to consider the cracks and fissures — both 

 large and small— which chalk contains, not only 

 at the surface, but at all depths. Water, when 

 percolating through chalk, acts mechanically by 

 abrasion and wear and chemically ; for after pass- 

 ing through vegetable soil, rain water becomes 

 charged with carbonic acid, which renders it a 

 ready solvent of carbonate of lime or chalk, and 

 this all adds to its water-bearing properties. From 

 this, I think we may imagine a saturition level 

 below our hills risin? and falling according to the 

 rainfall, teading to find its level with the North 

 Sea, but where we have big hills, owing to the 

 resistance to percolating water, we migbt reason- 

 ably expect, I think, the saturation line 

 nnder such a bill to be arched, in fact, 1 think we 

 migbt imagine the saturation line almost following 

 the surface lines, with the tendency to slowly find 

 its level. If I am right in imagining such a line 

 in saturation under the chalk hills, then all the 

 phenomena relating to the last fiow of the nail- 

 bournes can be explained. 



It was in 1902 that the wells in the Elham and 

 Petbam nailbourne valleys were last dry. These 

 wells are dug to a depth of sixty or eighty feet, 

 and the saturation level had fallen over eighty 



feet below the valley bottom — how much more 

 one cannot say. The heavy rains of liK)3 caused 

 the line of saturation to rise gradually, until in 

 December in the same year some of the wells were 

 overflowing,the8aturation level had risen above the 

 valley bottom level, and instead of passing under- 

 ground percolating in a northern direction, the 

 water issued at points all along the valley bottom 

 and was soon flowing along the entire course. 



In the spring of 1903. owing to the great rain- 

 fall, the wells throughout the district began to 

 rice and about July in the same year the wells, 

 between the springs on the line of saturation at 

 Well Chapel, and the two notable springs in 

 Bourne Park, had risen and the surface of the 

 water was now but a foot or so lower than the 

 water course through the valley. The first place 

 from which the water issued was from the two 

 springs in Bourne Park ; from here the stream 

 followed the old water course, gradually filling 

 the lake, but yet the saturation line was not 

 quite up to the valley bottom, but for several 

 weeks between the point where the watei entered 

 the alluvial and Weil Chapel, by raking away the 

 bottom of the water course, the water could be 

 seen in some instances just below the surface. It 

 was not until January, 1904, that the stream 

 flowed completely above valley bottom. Water 

 almost suddenly issuing from certain springs in 

 higher parts of the valley, is, I think, what gives 

 the idea of the cavity theory, but, it seems to me, 

 just what we might expect when we consider that 

 we have left the low lying marshes and entered a 

 district with plateau extending on each aide. 

 While standing in Bourne Park and looking up 

 the valley, we have on our left chalk hills, 250 feet 

 above sea level, extending from Bridge Hill to 

 Adisham, without a watershed, and on our right 

 we have hills extending towards Whitehill 

 Woods and Lower Hardres. If we imagine a 

 saturated line under these hills, tending 

 to find its level, but owing to the resistance 

 caused by the chalk, is held up almost to 

 the contour of the surface, when such a satur- 

 ation line rises above valley bottom, thiough the 

 tendency of the water to find it level, we might 

 reasonably expect under such conditions the flow 

 to start from the foot of the biggest hills, and also 

 we might expect as the saturation line fell, these 

 springs to be the las!; to cease— such was exactly 

 the case. The two springs in Bourne Park at the 

 foot of the plateau commenced to flow July, 1903. 

 The exces&ive rainfall continued through the 

 summer, autumn, and winter, and so saturation 

 level continued to rise. Villagers in Bishopsbourne 

 and Barham. whose wells were dry but a few 

 months before, found the water in them rising 

 steadily. In December saturation level had risen to 

 the valley bottom level. The alluvial deposit in the 

 valley was saturated for miles, and *ith but little 

 persuasion, water filled any hole one might dig. 

 The stream from Etchin Hill, higher up the 

 valley, did not lose itself so easily in the alluvium, 

 but continued its journey, and on December 24. 

 1903, quite a powerful stream occupied the old 

 course, but again the flow above the surface was 

 brofcen,althongh,flowing8tronglythroagh Barham; 

 it had not got far beyond, but proved to be con- 



