206 G. Boiclier — Water-supj^ly of East Kent. 



Nailbourne may run for two years in succession ; on other occasions 

 it may not appear for two, three, or four successive 3'ears. 



Matthew Beli, Esq., writes to me to the effect that in dry seasons 

 his ponds became dry when the Nailbourne was not running, and 

 being convinced that all the time at Bourne Park the water was 

 finding its way down below ground, he caused a trench three feet 

 "wide to be sunk across the valley, through the underground stratum 

 of gravel (which he then ascertained to be about 12 to 15 feet in 

 thickness), into the Chalk below, and then filled this trench with 

 stiff puddle, forming an underground dam. The water, as he 

 expected, immediately began to rise, and the sheet of water opposite 

 his house has never been dry since. A reference to the section which 

 I have prepared to illustrate this paper will perhaps explain the 

 action of this Nailbourne better than a mere verbal description. 

 It will be seen that the beds dip at a considerable angle from south 

 to north ; at the former the impervious beds of Chalk Marl and 

 Gault Clay cause the water to gravitate in the porous Chalk strata 

 from south towards the north. The water from the Chalk is derived 

 in the first instance from the rain falling on its surface. This takes 

 a considerable time to find its way down to the impervious bed ; and, 

 after doing so, to spread laterally through the surrounding strata. 

 It is evident that when the Chalk is saturated icitJi loater, the 

 water-level is correspondingly raised. It happens that it is some 

 time after the abnormal rainfall, before it affects the water-level 

 of the wells, and consequently before the lower strata become 

 saturated with water. When this is the case, the water finds its way 

 out at the surface, and runs down the valley. It may at first sight 

 appear strange that springs should break out at Postling and Horton, 

 as the beds dip in the contrary direction to the flow ; but if you con- 

 sider that the impervious beds of clay there come to the surface, and 

 the rainfall takes a long time to expand laterally through the Chalk, 

 you will understand that it will here find vent where there is the 

 least resistance. 



An examination of the section will show also that the water-level 

 by no means corresponds with the height above the sea-level (a very 

 prevalent error). It will be seen that the water-level in the wells at 

 Acrise, Horton, Elrasted, and Wootton, stands at a level some two 

 hundred feet or more above those at Canterbury. These well-sections 

 are placed to scale at their respective heights, and the water-level of 

 the wells is shown by a shaded line. Most of these wells are dug in 

 the Chalk, not bored, and many of them have been deepened in dry 

 seasons, so that in this case the well depths represent pretty nearly 

 the ordinary water-level in dry seasons ; for it is impossible to get 

 these wells sunk to any considerable depth below the point of 

 saturation or water-level in the Chalk. For instance, Mr. Collett, of 

 Elmsted Kectory, who has dug a well 277 feet deep, states : " The 

 springs rise and fall here in a wonderful way ; they are usually 

 highest in May, and fall till January, when they begin to rise again. 

 In 1884, Jan. 13, the well was dry, next day it rose 14 feet; the 

 water varies in height from 13 to 63 feet." Mr. Metcalfe, of Upper 



