Underground Water. 563 
of petroleum will continue to be of immense practical importance ; 
but coal will doubtless remain our great ultimate source of power. 
An obligation rests upon us to see that the oil resources of the 
British Empire and of territories within our influence are explored, 
if possible, by British geologists, with all the specialized knowledge 
that can be brought to bear; and I am glad to think that the 
University of Birmingham and the Imperial College of Science and 
Technology, London, with this end in view, are doing pioneer work 
in giving a systematic and specialized training to our young petroleum 
technologists. . .. 
Underground Water. 
Since the year 1856, when the Frenchman, Darcy, attempted by 
a mathematical formula to express the law governing the trans- 
mission of water through a porous medium, nearly all investigation 
upon this important engineering question has been carried on in the 
United States; and many of the results have been published in the 
valuable Water Supply and Irrigation Papers of the United States 
Geological Survey. Particular reference should be made to the work 
of Hazen, King, Darton, and Slichter, the last of whom has given us 
the clearest and most convincing explanation of the behaviour of 
water percolating through a porous rock. He and his co-workers 
have experimentally investigated the factors which determine the 
underground flow, and expressed their relationship by mathematical 
formule ; and they have made it clear, by careful measurement | 
extended over long periods, that the rate of flow through average 
porous water-bearing rocks and under ordinary pressure gradients is 
extremely small, something like a mile a year, or even less.! 
Geologists who are in touch with the application of these principles 
to such engineering matters as water-supply, sewage, and drainage 
will readily appreciate the great value of such researches. At the 
same time, one must reluctantly confess that, with few exceptions, 
the investigations have not been adequately grasped and utilized 
in present-day engineering practice in this country. As to their 
geological bearing, we have only to be reminded of the important 
processes of solution, cementation, and fossilization in rocks in order 
to comprehend the value of a just estimate of the behaviour of this 
vast. and slow-moving chemical medium in which the superficial 
rocks of the crust are immersed. . . . 
The conditions are so complex and the controlling factors vary so 
much in different river-basins that it is impossible to obtain for the 
whole country anything like an accurate and reliable expression for 
the relationship between rainfall, percolation, and run-off. The 
interminable and costly legal wrangles during the passage of a Water 
Bill through Parliament bear witness to the truth of this statement. 
What is needed is a continuous record in the different catchment 
areas of the country of observations on river discharge, percolation, 
and so forth, extended over many years. Fortunately, our rainfall 
observations, thanks to the British Rainfall Organization, are now 
1 Slichter, Water Supply Paper No. 67, U.S. Geol. Surv.: ‘‘ The Motions 
of Underground Waters.’’ 
