CONTRIBUTIONS OF GEOLOGY 201 



moment the opposing forces began " digging in." At least two 

 such generals were among Col. David's superiors at Head- 

 quarters, and the success he was able to achieve in the practical 

 application of engineering geology to military projects was 

 no doubt partly due to the breadth of vision of men of this 

 stamp. One of these generals admitted that in the beginning 

 army officials were as a rule very skeptical as to the practical 

 importance of Col. David's geological theories. But, he added, 

 after several bad blunders due to refusal to take geological 

 advice, and several striking demonstrations of Col. David's 

 ability to predict accurately the conditions which would be en- 

 countered in depth by underground workings, they were so 

 far convinced that before the end of the war no responsible 

 officer in the British Army would consider the planning of such 

 works without first securing the opinion of a geological ex- 

 pert. 



The non-geological reader will have no difficulty in under- 

 standing the importance of geological aid in selecting locations 

 for excavating mines, tunnels and dugouts, if he will remem- 

 ber that some rocks are porous and permit the ready passage 

 of water, whereas others are more or less impervious. Now 

 it happens that along part of the front one rock formation, 

 through which comparatively little water circulated, had 

 both above and below it layers carrying great quantities of 

 water. If the army engineers kept their tunnels or other 

 excavations well within the non-saturated bed, all went well. 

 But as soon as they got too high or too low, water burst through 

 from the adjacent formations and flooded their works. Only 

 a geologist familiar with every detail of each formation could 

 guide the underground work so that it would be sure not to 

 end in disaster. At Messines Ridge, where precisely these 

 rock conditions existed, very careful geological examinations 

 were made on the ground, in addition to work done at the 

 Geological Survey office in London. Thus the most exten- 

 sive military mining operations in all history were undertaken 

 on the basis of geological study. That they were successful 



