Graphic Representations 893 



gain a mental picture of acute structural relief when, in fact, the tectonic 

 relief may be very mild. . . . Exaggeration of vertical scale affects primarily 

 the vertical dimensions of a geological form but it also affects, in a certain 

 way, the horizontal dimension. In the vertical direction the picture is actually 

 expanded; in the horizontal direction it is apparently contracted. . . . Vertical 

 expansion causes distortion of dip and thickness of beds and this distortion 

 varies with true dip and ratio of exaggeration. . . . The principal horizontal 

 or lateral effect of exaggeration of vertical scale is to bring every element of 

 a section closer together. 



Prime factors to consider in preparing geologic cross sections are the 

 lithologic plot (in part or in whole), the name and age of the formations, 

 the natural as well as the exaggerated profile, proper captioning, a plan 

 map showing the line of section, the vertical and horizontal scale, and the 

 legend. 



Control stratigraphic columnar sections should accompany the cross 

 section as they contribute to a better understanding of the stratal sequence 

 and relationships of the units involved. Unconformities and lithofacies 

 boundaries should be shown. An excessively long cross section may be 

 broken or interrupted. 



The Busk method (fig. 447) of constructing geologic cross sections 

 is frequently used by geologists. This method is applicable to many struc- 

 tural problems although its limitations must be recognized. Requisites for 

 its use are adequate dip control, parallel folding, and constancy of forma- 

 tional thickness. 



Figures 436 to 466 are included for the purpose of suggesting various 

 methods of compiling and presenting subsurface data. 



Questions 



1. Why should geologic reports contain numerous graphic representa- 

 tions? 



2. What data should be recorded on well-log headings? 



3. When should the percentage log be used? 



4. Review the abbreviations commonly used in giving lithologic descrip- 

 tions on well strips. 



5. Give the colored-well symbols for the following lithologies : dolostone, 

 arkosic sandstone, ferruginous sandstone, arenaceous shale, tuff, and 

 arenaceous limestone. 



6. Study figure 432 which typifies data to be included on a final well 

 log. 



7 Discuss the percentage and interpretive log strip on plate 12. 



8. Give the symbols for the following: drilling well, producing well, 

 abandoned gas producer, strong-gas show, salt water, slight-oil show, 

 faint-oil smell, coarse crystalline, detrital chert, pyrite, microfossil, 

 medium-grained sandstone, and insoluble residue. 



9. Why should geologic cross sections be drawn to natural scale? 



