32 HULL SCIENTIFIC AND FIELD NATURALISTS’ CLUB. 
and is supplied with fresh water entirely by the rain which 
falls upon its outcrop. All surface and subterranean streams from 
other districts are completely cut off, on the one side by the 
sea, and on the other side by the raised outcrops of the underlying 
clays and the accumulations of drift at the foot of the chalk 
escarpment. Moreover, the rain which falls upon the drift clays 
of Holderness is also cut off from the chalk below, and is chiefly 
conveyed to the Humber by surface streams and drains. 
The outcrop of the chalk or area of absorption, is, roughly 
speaking, about 300 to 350 square miles, a little more than half 
the extent of the whole of the water-bearing area included between 
the sea and the outer limits or termination of the chalk. The rain 
which falls upon this outcrop, known as the chalk wolds, less that 
portion intercepted by animals, cisterns, ponds, and plants, and 
taken up by evaporation, is absorbed by the porous soil, and 
descends through the rock until arrested by the unstable water- 
line in the chalk. This water-line is not a horizontal plane, but 
rises northwards and westwards, and somewhat resembles the 
contour of the chalk in which it is contained.* 
The water beneath Holderness is held down by the super- 
incumbent clay, and except at times just along the outer edge 
of this clay, it always remains at the same height. But, whenever 
the clay is pierced by boring, the water rushes upwards to within 
a few feet of the surface. Leaving the edge of the clay and 
proceeding either northward or westward, the unrestrained 
water-line begins to rise into an incline, the incline in some places 
being greatest when the water-line stands the highest in the rock. 
As this line gradually falls from long absence of rain, its general 
inclination becomes less and less marked.t In the Mid Wolds 
it is liable to great variation. In November and December, 1874, 
the water in Langtoft well sank to 130 feet below the surface 
of the ground, and the well had to be deepened several feet before 
the water-line was reached; while on the gth January, 1877, 
the water in the same well reached within 27 feet of the surface, 
thus showing between the two dates a variation of 103 feet in the 
height of the water-line. But on the above dates at the edge 
of the clay at Driffield, six miles to the south of Langtoft, none of 
the service pumps failed to raise the water. On the 9th January, 
1877, the water-line in Cowlam well, at an elevation of about 
430 feet above sea level, and about 24 miles W.S.W. of Langtoft, 
* From many years of personal observation on the chalk wells, situated in my 
native county of Berkshire, I have noticed that the water-line has a strong 
tendency to follow the contour of the chalk.—H.P.S. 
1h sags also holds good of the wells situated on the Berkshire Downs.— 
H,P.S. 
a 
