CONTRIBUTIONS OF GEOLOGY 203 



of any kind. They gave to the water supply officer of each 

 army the geological advice he was required to seek before put- 

 ting down any well, and told him where, how deep, and in 

 how great quantities he could expect to find good water. They 

 provided these same officers with various water-supply maps 

 and with geological cross-sections showing the conditions un- 

 der which underground water occurred at all points along the 

 front. They told where older rocks suitable for road metal 

 protruded through the later covering deposits, and where the 

 best rocks for concrete, cement and other purposes would be 

 found. And since it was important to know what sources of 

 valuable rocks and minerals the enemy had at his command, the 

 geologist's knowledge of the rock formations and the mineral 

 deposits of enemy countries was placed at the service of the 

 army to provide this information. 



Artillery fire produces very different effects on different 

 types of soil and rock. One type of shell may produce the 

 greater damage in a clay formation, another in a loamy soil, 

 still another in limestone or chalk. The geologist was able to 

 tell the artillery officer what kind of formation his fire was 

 directed against, and thus to aid his judgment as to the type 

 of fire he should employ. When a big attack is planned, it is 

 vitally important to know just what surface conditions the 

 troops advancing into the enemy's area will find, as plans for 

 the advance will vary according to the kind of obstacles to be 

 encountered. It is evident that the heavy barrage fire preced- 

 ing such an attack must profoundly alter the surface of the 

 country to be passed over, and that the nature of the alteration 

 will depend upon the kind of soil or rock beneath the surface. 

 The shell craters may be large and deep in some formations, 

 shallow but broad in others, in still others imperfectly devel- 

 oped. In one formation water will accumulate in the shell 

 craters if it rains, but not otherwise ; in another water will in 

 any case be admitted because the bottoms of the craters pene- 

 trate a water-bearing bed; in yet another no water will stand 

 in the craters no matter what the weather may be. It should 



