45 
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. ‘he 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 with water, 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, Elmsted, 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, 80 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 Rectory, 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 
Hardres Rectory, writes, “This well was formerly 300 feet deep, but 
failed in the dry seasons of *56 and ’58, when it was deepened 
60 feet. The water-level lowers in autumn from 20 to 30 feet.” 
