Ratio 



The ratio contour map shows the ratio of the aggregate thickness of one 

 lithologic class to that of the remaining classes that go to make up the complete 

 section. For example, a sandstone ratio map shows the ratio of sandstones to all 

 other rock types. Thus the ratio value of sandstones in the section shown in 



Figure 24-25 is ^ , ,.,. , ._ = 0.51. The value 0.51 is plotted on the 

 160 + 110 + 45 



map, and all others are computed in a like manner; then the sheet is contoured 



like an isopach map. A separate ratio map may be made be for each of the 



lithologic classes considered in the analysis. 



Percentage 



The percentage contour map is very similar to the ratio map, except that 

 the number used for contouring is the percentage value of sandstones, for 

 example, in the total thickness of the formation. Thus, in the log in Figure 24-25, 



this number is = 0.34. Although the numerical values of the contours 



478 



will be different from those on the ratio map, the general appearance of the 



map should be the same. 



STAT E '. COLO HA DO 



FORMATION : PERM/ AN 



Figure 24-27. Lithofacies-data sheet. 



Isolith 



The term isolith was first applied to the imaginary surface separating 

 two adjacent but differing lithofacies. However, the term is now commonly used 

 in an entirely different sense. Perhaps it is unfortunate that this situation has 

 come about, but inasmuch as the trend is strongly developed toward the newer 

 usage, the following discussions are based on these definitions: 



485 



