414 REPORTS ON THE STATE OF SCIENCE, ETC. 
small a time limit as possible (say one week or less) for-each chosen period 
of the year. _In some wells at which continuous pumping is not going on 
the levels might be taken daily or weekly and related to rainfall, percolation 
and -evaporation. ‘These would give a more continuous picture of the 
fluctuations of the water-table during the year. 
Local co-operation would be necessary to gather widespread and consistent 
data for drawing contours; but the selection of the wells and the general 
supervision might be the task of a hydrogeologist. Some central authority 
is needed to encourage a standardised procedure and receive the necessary 
data for the construction of a continuous series of contoured maps. 
The seasonal fluctuation in the water-tables at or near outcrop would 
appear to depend upon :— 
(1) Percolation and evaporation ; (2) issue from springs ; (3) pumping. 
At trial borings and established pumping stations records are needed of. 
(1) the actual amount of water pumped (stating whether working at full 
capacity); (2) the maximum fall in water level during pumping; (3) the 
rate of lowering of the water level; (4) the rate of recovery after cessation 
of pumping; andsoon. Cones of depression in the surface of the water- 
table should be mapped out and related to the diameter of the well or 
boring, the suction level, capacity of pumps, physical character of the 
water-bearing rock and other relevant factors. 
Arising out of the plotting of water-table contours, the effects of pumping 
on the general, as distinct from strictly local, water-table over a number 
of years could be studied, and the results of overpumping—with possible 
deterioration of the water both in quantity and quality—properly evaluated. 
Amongst associated rocks with different degrees of permeability, perched 
water-tables are to be expected. 
Isolated wells—In areas where isolated or very widely spread wells 
occur it may not be possible to construct either contours or sections of the 
water-table (even if present); yet the original geological details, and 
subsequent continuous pumping records, will be useful guides to estimating 
prospects for future boreholes in the neighbourhood. Their value: will 
increase as more and more wells are sunk. 
Springs and wet-lines —All springs should be marked down and ganged 
consistently. They are the headwaters or subsidiaries of surface streams 
fed from underground storage and occur (1) as overflows from permeable 
rocks at positions where the water-table cuts the surface of the ground— 
as in the Bunter Sandstone area of Sherwood Forest, or in Chalk districts; 
where also ‘ bournes’ commence to flow when the water-table rises above 
a certain level; (2) as isolated and unrelated issues from irregular. systems 
of fissures in less permeable rocks. As a rule springs are much more 
regular in yield than the streams they help to feed, and, like rivers issuing 
from lakes, far less liable to rapid fluctuations. 
It may be:noted that geologists frequently discover previously eens riick 
springs, especially alongside, and in the beds of, streams during low-water 
periods. ‘They also note and usually map ‘ wet-lines ’ or lines of seepage— 
the potential sources of springs—and relate them to the local geology. 
Data of this kind are extremely valuable when local water supplies or 
impounding schemes are in question, and are especially desirable in 
districts—such as those of predominantly shaly, slaty or granitic rocks— 
where no water-table, in the ordinary sense, is to be expected. 
Quality of water (mineral). —A point that requires research is that of the 
potability of water apart from the effects of organic pollution. In certain 
cases waters in formation near outcrop, and for a short distance beneath 
cover, are potable, but become increasingly hard, saline, and unpotable 
