COMPOSITION OF THE OIL-FIELD WATERS. 
79 
Figure 5. —Variation in chemical character of waters from different depths, showing alterations by 
hydrocarbons. The horizontal lines represent the horizon of the waters and on these lines are 
plotted their analyses. (See analyses 74 to 79, Table 12.) A, Four waters from neighboring oil wells 
in sec. 36, T. 20 S., R. 14 E., Coalinga field. (Note reversal of sulphate and carbonate values as the 
oil zone is approached.) B, Two waters from a well in sec. 27, T. 18 S., R. 15 E., several miles north 
of Coalinga field. (No oil was found to a depth of more than 3,700 feet, and the waters are prol> 
ably unaffected by hydrocarbons. Note constancy of sulphate and carbonate values.) 
