172 W. CROSS GEOLOGY IX THE WORLD WAR AXD AFTER 



munication subways, galleries, dugout. chambers for various purposes, all 

 on a scale never before seen in warfare. Besides these excavations, there 

 are the works of the Sanitary Corps for the establishment of a water sup- 

 ply, drainage, cess pits, disinfecting and germicidal plants; and in addi- 

 tion there are the roads and railroads, artillery emplacements, ammunition 

 dumps, depots for supplies, etcetera, located near the front lines, the 

 efficiency of which is distinctly influenced by the geological conditions. 



We are familiar with the fact that these opposing systems of military 

 works, extending for hundreds of miles, traverse a great variety of geo- 

 logical formations, ranging from the dune sands and marshes of Flanders 

 to the crystalline rocks of the Vosges Mountains. They cross sections of 

 Tertiary, Cretaceous, Jurassic, and Triassic sediments, including chalk, 

 limestone, sandstone, shale, marl, clay, and various transition rocks, as 

 well as valley and slope deposits of recent age. It is history that for three 

 years and more this general line suffered many minor changes or readjust- 

 ments — sometimes forced, sometimes voluntary. 



N"ow no geologist or engineer who has dealt with problems involving 

 rocks and imperfectly consolidated geological formations can fail to see 

 how an experienced stratigraphic geologist and lithologist, accustomed to 

 study similar formations in the field and to make, interpret, and use geo- 

 logical maps, could render great assistance to the military engineer in the 

 development and improvement of this stupendous project; nor can the 

 thought he avoided that if one of the antagonists along this battle zone 

 has possessed and used a superior Knowledge of the local roclcs and their 

 distribution — that is, the geology — it has cost his opponent dearly. It 

 is to be feared that the Germans have profited greatly in this use of the 

 expert geologist. 



Let us now consider briefly the nature of the civil and military engi- 

 neering problems involved in constructing, maintaining, defending, or 

 attacking a great system of field fortifications such as has been described, 

 which must traverse all the formations named. The work is largely exca- 

 vation, of varAdng ease or difficulty, according to the rocks concerned. 

 Under most conditions there is some opportunity for choice as to the site 

 of the trench, subway, or dugout. A shifting of the trench line a few 

 yards may greatly increase or decrease the difficulties of the task. The 

 underlying rocks are often obscured by soil, weathering products, or veg- 

 etation, so that without geological data the conditions to be encountered 

 below the surface can not be foreseen. The walls of trenches may give no 

 suggestion as to the existence of rocks below in which needed dugouts or 

 tunnels may be excavated with ease, while a knowledge of the stratigraphic 

 section may show that favorable conditions are to be expected. 



