WAR GEOLOGY 173 



But the problems of the rocks themselves are simple compared with 

 those connected with the presence of water in those rocks, circulating 

 through certain strata, of ground water, or the rain and snow water of 

 the surface. The water-bearing strata may furnish a desired supply for 

 the troops or, when cut, may cause the flooding of extensive works. Again, 

 the water-soaked trenches in impermeable clays may possibly be drained 

 by boring or cutting into a porous permeable stratum. The depth of 

 ground water level practically determines the feasibility, or the reverse, 

 of securing dugouts in certain areas, and of mining and sapping opera- 

 tions. The knowledge of the ground water level and its seasonal variations 

 is of great importance in many districts. I need not dwell on this. 



The effect of surface water on the rocks forming the walls of this vast 

 system of excavations is of critical importance, especially during the 

 rainy season and in time of melting snows. Marly beds simply dissolve 

 and the trench walls slump down. Other rocks require strong revetments 

 or other supports; jointed shales and fractured rocks may slip as land- 

 slides into the trenches, and where drainage can not be effected a terrible 

 condition of mire and filth soon arises. 



The difficult problems arising from the combination of conditions so 

 inadequately sketched are those with which the expert stratigrapher and 

 hydrographic geologist are specially fitted to deal. By means of personal 

 observation and by the interpretation of geological maps or reports, the 

 geologist can reach an understanding of the situation more quickly than 

 any other person. It is particularly in the avoidance of difficulties that 

 his advice is of value. His ability to project or apply the information 

 of a section of rocks obtained in one locality to surrounding or even to dis- 

 tant areas enables him to give advice bearing on plans of operation suffi- 

 cient to save precious time, labor, and often the lives of men. Without 

 such advice important parts of the defensive system may be much weaker 

 than need be, perhaps to the degree that they must be abandoned even 

 without attack by the enemy. 



Up to this point only natural difficulties of making and maintaining 

 this system of field-work have been considered; but each svstem is subject 

 to the greatest damage, even to complete demolition, that an aggressive 

 enemy can inflict. That there has been a considerable development of 

 this type of the offensive we can not doubt, but details of what has been 

 •^r^complished or suffered are as yet scanty, for evident reasons. We can 

 be sure, however, that here, as in the construction of the works, the more 

 complete the understanding of the geological conditions the better. It is 

 a battle of wits, and the side possessing the more thorough understanding 



