636 whitmore. MILITARY GEOLOGY [Ch. 34 



to responsible officers it is not, of course, necessary to present the steps 

 by which the conclusions were reached. Almost all terrain-intelligence 

 interpretations are made by deducing, in whole or in part, the geologic 

 history of the area in question. It is in this stage of study that the 

 principles of sedimentation and other basic geologic principles are 

 used. The reasons for not presenting these deductive steps to the 

 military users of the data are obvious: they have neither the time 

 nor the specialized training to examine what, compared to the vast 

 scope of a military operation, are minutiae. The necessity of present- 

 ing conclusions therefore places a heavy responsibility on the military 

 geologist. Their reliability will differ widely, depending on how much 

 basic information (geologic reports, maps, aerial photographs) is avail- 

 able. A reliability rating system was used in most military geology 

 reports in World War II. 



Because of the factor of expediency in military operations, the tend- 

 ency has been to define the engineering properties of earth materials 

 qualitatively, not quantitatively. This is illustrated by Table 1, a 

 portion of a larger table prepared by von Billow (1938). 



Terrain Appreciation 



In preparing an intelligence report for planning purposes, or in the 

 more detailed work of preoperational intelligence, it is best to learn 

 as much as possible about the entire area involved, even though im- 

 mediate intelligence needs may apply only to part of it or to one as- 

 pect of regional knowledge such as, for instance, location of material 

 for concrete aggregate. 



Accordingly it is standard practice in military geology to prepare, 

 first, generalized geology and soils maps of the assigned area and, 

 on the basis of these, to construct a terrain-appreciation map. The 

 latter is best described as an applied physiographic map (Fig. 1). 

 With its accompanying text, it is designed to emphasize important land 

 forms, such as cliffs, steep slopes, and reefs; to summarize ground con- 

 ditions, bedrock types, and kinds of vegetation; and to inform the 

 reader briefly and clearly of the most feasible corridors for movement 

 and of barriers that will prevent movement; of cover (protection from 

 enemy fire), such as ravines and boulders, and concealment, such as 

 brushy woods or sugar cane. The best points of observation are in- 

 dicated, and the problems of constructing hasty fortifications pointed 

 out. 



The military geologist seldom has a geologic or soils map of the en- 

 tire area in which he is interested. If he has detailed information 

 covering a part of his area, he can extrapolate, on the basis of the 



