204 THE NEW WORLD OF SCIENCE 



therefore be evident that maps showing the kinds of surface 

 troops will have to cross following heavy barrage fire must 

 be of great value to an army commander. The British geolo- 

 gists prepared maps of this kind for much of Belgium and 

 northern France. 



Tanks can advance over certain kinds of soil, but their great 

 weight causes them to sink deep and become mired in others. 

 So it became important to know in advance what were the soil 

 conditions behind the enemy's lines. " Tank maps " were 

 therefore produced by the geologist, showing where tanks could, 

 and where they could not go. 



Before retreating an enemy aims to destroy all the wells 

 and springs in the country, in order that the pursuer may be 

 as seriously handicapped as possible. For this reason the 

 army commanders depended upon the geologists to prepare 

 maps showing underground water supplies of enemy territory 

 into which it was proposed to advance. These could be based 

 in part upon published data available in the geological libraries 

 of Allied countries, and in part upon long experience with 

 water-bearing beds within the Allied lines which were known to 

 extend under enemy territory. It was found possible from 

 published maps of enemy areas to construct geological cross- 

 sections of the country behind his lines, locate on these sections 

 the water-bearing horizons, and then by making allowance for 

 the surface topography, to prepare in advance maps which 

 indicated with reasonable accuracy just how deep the advanc- 

 ing armies must sink wells in any given locality in order to get 

 the fresh water supplies they would require. 



Enough has been said to give the reader some impression of 

 the wide range of service performed by the geologists attached 

 to the British Expeditionary Force in France and Belgium. 

 I think it is fair to say that in no other Allied army was 

 geological science so largely and so successfully employed. 

 If we turn to the record of the French Army, it does not ap- 

 pear that the services of their geologists were utilized to any 

 great extent, although a limited amount of geological work 



