COMPOSITION OF THE OIL-FIELD WATERS. 
61 
amount, constitute an unusually high percentage of the total solids. 
The alkalies are exceptionally low, though chloride predominates 
over sulphate. No. 21 is somewhat similar in character to the last. 
In the locality from which this water was obtained the oil measures 
are only 650 feet below the surface and the water 304 feet. The 
water is essentially a shallow type and yet has undergone some 
alteration, as evidenced by the higher ratio of carbonate to sulphate 
and by the presence of hydrogen sulphide. No. 20 is somewhat 
similar to No. 21 but more nearly resembles the types represented 
by the preceding analyses. Analyses 22 and 24 represent very 
similar top waters, both being pronounced secondary saline types. 
No. 23 is a water characterized by a small percentage of primary 
alkalinity, but it is included here because of its very low carbonate- 
sulphate ratio and its very high sulphate salinity ratio. 
Analysis 25 represents a water encountered at a depth of 670 feet 
in Midway Valley. This water is very similar in composition to No. 
87, discussed above, and represents as near an approach to normal 
connate water as can be expected. Its reactive properties resemble 
those of sea water (see analysis 52, Table 8, p. 73), though the 
secondary salinity is rather low. The sulphate salinity ratio is about 
that of sea water and therefore much lower than in the shallow 
meteoric types. The. carbonate-sulphate ratio is about normal for 
either the meteoric or the connate type. The concentration is almost 
three-fourths that of sea water. It is noteworthy that this water 
occurs in that part of the McKittrick formation correlated with the 
Tulare formation, which consists of deposits laid down in fresh water 
and which probably has never been submerged beneath the sea. 
Assuming that the sample was correctly taken, this water therefore 
presumably represents sea water that was originally entrapped in 
the marine strata below, and that has since migrated to the higher 
beds. Such an ascent would indicate considerable artesian pressure 
and would imply that the escape of the deeper waters by migration 
along the lines of stratification is practically cut off. If this explana¬ 
tion is correct it throws light on the completeness with which the 
connate water is trapped in the Midway syncline. 
Analysis 26 represents sulphur water from a well drilled near the 
outcrop of the oil measures which probably penetrates the shale of 
the Monterey group. The presence of hydrogen sulphide and also 
the somewhat high carbonate-sulphate ratio indicate that this water 
has been slightly modified, but it is included here because of its 
secondary salinity. Owing to the proximity of the outcrop of the 
sand there has been a considerable admixture of meteoric (sulphate) 
water, and chloride is not so high as in the waters farther east. 
Several other wells drilled in the brown shale just west of the western 
edge of the Midway field have obtained similar sulphur water, but, 
