Subsurface Maps and Illustrations 



945 



terns in black. This can be done much more effectively by colors. The best 

 practice is to represent the variations within a given lithologic class by 

 colors restricted to a definite range of hue and tone; for example, the sub- 

 divisions of limestones on a limestone isolith map should be shown by 

 various shades of one or two basic colors chosen to represent the carbonate 

 group; on the sandstone isolith, by shades of the basic colors selected to 

 represent coarse clastic rocks. This procedure obviously must be varied 

 when the facies separation is made on the basis of rock color. The only 

 logical map presentation in this case is to show the rock color facies by 



Figure 507. Limestone isolith map. 



a similar color on the map; e.g., red rocks with red colors and gray with 

 gray colors. 



The chart in figure 509 will serve as a guide for coloring lithofacies 

 maps. When colors are used to represent lithologies, it is possible to show 

 gradations from one facies into another by alternate bands of color; for 

 example, where a sandstone facies grades laterally into a limestone facies, 

 the area of gradation would be shown by alternate bands of blue and 

 yellow or brown. If the proportions of sandstone to limestone are two to 

 one, respectively, then the yellow bands should be twice as wide as the 

 blue. This plan can be extended to include several color bands. 



Figure 510 is a lithofacies map drawn in black and white, with certain 

 patterns representing colors, which, in turn, represent the different rock 

 types. For very simple drawings like these the patterns are satisfactory; 



