PRESIDENTIAL ADDRESS. 391 



oil could not be maintained for many years. Owing to the almost certain rapid 

 increase in the output of coal, estimates made by the authority already quoted 

 indicate that the total production of petroleum could never reduce the world's 

 output of coal by more than about 6^ per cent." 



For us, and probably for those of the next generation, the geology of petro- 

 leum will continue to be of immense practical importance ; but coal will doubt- 

 less remain our great ultimate source of power. -d • ■ i. 



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 specialised knowledge that can be brought to 

 bear; and I am glad to think lliat 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 specialised training to our 

 young petroleum technologists. 



Underground Water. 



It is pleasant to recall that this Section of the British Association has in 

 the past done yeoman service in stimulating investigation and in collecting 

 valuable data which have a direct practical and economic application. As far 

 back as 1874 a Committee of Inquiry was ' appointed for the purpose of investi- 

 gating the Circulation of Underground Waters in the Permeable Formations of 

 England and Wales, and the quantity and character of the water supplied to 

 various Tmvns and Districts from these Formations.' For many years this 

 Committee compiled records of borings, which might otherwise have been lost, 

 and some of the local Scientific Societies affiliated to this Association did similar 

 work in their respective districts. 



Since the year 1856, when the Frenchman, Darcy, attempted by a mathe- 

 matical formula to express the law governing the transmission of water through 

 a porous medium, nearly all investigation upon this important engineering ques- 

 tion 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 perco- 

 lating 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 formulae ; 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 appre- 

 ciate the great value of such researches. At the same time, one must reluctantly 

 confess that, with few exceptions, these investigations have not been adequately 

 grasped and utilised 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 fossilisation 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. 



A wide and fertile field of research has been opened up to the mining geolo- 

 gist by the recognition of the important role played by ground-water in ore- 

 genesis and in the ' secondary enrichment ' of ores. In this country, however, 

 the circulation of underground water, and especially the relation of rainfall and 

 ' run-off,' concern the civil engineer more than the miner. There exist, unfor- 

 tunately, much confusion and iincertainty in engineering practice in regard to 

 such geological questions ; and this is due partly to a want of precision in the 

 use of terms, though mainly to a lack of reliable d.ata. One finds, for example, 

 frequent discrepancies in statistics of rainfall in relation to percolation and 



^' H. S. Jevons, British Coal Trade, 1915, p. 716. 



" Water Supplv Paner, No, C7, V.!^. Geo], Sur. -. ' The Motions of Under- 

 ground Waters, '-—Slichter. 



