GEOLOGY IN SERVICE OF MAN WATTS 279 



into full account, an elaborate geological survey at a ver^^ early 

 stage would in most cases more than pay its way. Such a survey 

 Avould not only give a good preliminary idea of the nature and 

 tectonics of the rocks underlying sites of dams and reservoirs, but it 

 would save its cost in limiting the number and in giving rational 

 direction to the inevitable pits which must be sunk, by restricting 

 them to the elucidation of points which the surface mapping leaves 

 obscure. It would at the same time direct attention to the innumer- 

 able pitfalls which sites often present and would generally provide 

 on the spot much of the requisite material for construction. 



It is an arguable question whether the expenditure of such vast 

 sums as have been devoted to the supply of large towns is entirely 

 justified. The provision of a single supply, of which large quantities 

 are used for drinking, cooking, and industrial purposes, necessitates 

 that the water shall be of immaculate purity, and this pure sub- 

 stance, the purest of all the things we consume, is employed — may 

 we not say wasted — for flushing, washing, and a host of other 

 purposes for which a less pure water would suffice. Surely the time 

 has come when people could be educated up to the use of a dual 

 supply, and this should be a commercial possibility where the area 

 served and quantity used are really large. The experience of London 

 has shown the very high cost of a single supply to all consumers and 

 for all purposes, and the limits of future supply are almost in sight. 

 It seems to be time that the problems of a dual service should engage 

 serious attention. 



Power. — Owing to the configuration and rainfall of the British 

 Isles, and their congested population, Ave are apt to think of water 

 questions in terms of supplj^, and, though we are using a certain 

 amount of water for power, there is only a limited development pos- 

 sible. In many other parts of the Empire, however, this is becoming 

 a valuable asset, and nowhere more than in Canada, which is rapidly 

 developing its resources on a very large scale. AVhat has been said 

 with reference to water supply is of equal application here, for the 

 physiographic conditions which bring about steep gradients accom- 

 panied by large bodies of water, introduce factors of denudation, 

 transport, and deposition by the water which call for most careful 

 selection of sites for reservoirs and works, if the all too frequent 

 disasters are to be avoided, and if the schemes are not to be ephem- 

 eral in duration and excessively costly in upkeep. 



With sources of power other than coal and water — including that 

 of the tides — the geologist has little concern. But there has been 

 brought into service at Volterra, in Italy, a new source of power in 

 the high-temperature steam from fumaroles which had previously 



