60 
OIL-FIELD WATERS IN SAN JOAQUIN VALLEY, CAL. 
secondary saline in character and high in sulphate, whereas those 
near the oil are primary alkaline and free from sulphate. However, 
there are many intermediate types which show primary alkalinity 
and still retain a fairly high proportion of sulphate. For con¬ 
venience in discussing the waters of the fields of the west side the 
secondary saline waters high in sulphate have been referred to the 
normal group and those of primary alkaline character containing 
considerable sulphate to the modified group. The line of demarca¬ 
tion is therefore assumed to be the point at which secondary salinity 
disappears and primary alkalinity appears. As a rule this division 
is justified, for the decrease of secondary salinity is probably due as 
much to the normal increase of alkalies with depth as to actual 
decrease of sulphate. However, when sulphate is very high and the 
alkalies are proportionately less abundant than usual, the property 
of secondary salinity may be retained after some of the sulphate 
has been removed. Analyses 21 and 26, for example, represent 
sulphur waters, the hydrogen sulphide being presumably due to 
the reduction of some of the sulphate, yet both of these waters are 
secondary saline and are therefore grouped with normal types. As 
an additional criterion of the alteration of the waters the ratio of 
carbonate to sulphate is shown in Tables 3 to 7. It will be noted 
that in all of the analyses in Tables 3 and 4 except Nos. 19 and 21 
this ratio is less than 0.25, and that No. 21 is a sulphur water which 
has doubtless been somewhat modified. This ratio explains another 
apparent inconsistency in Table 3, namely, the inclusion of No. 17, 
a primary alkaline water, with the normal secondary saline waters. 
In this water the sulphate is extremely high in comparison with 
both chloride and carbonate and the appearance of primary alkalinity 
is due rather to the abnormally low proportion of alkaline earths than 
to any loss of sulphate. As already stated, no single property or 
constituent of a natural water can be a universal criterion of its 
relation to the oil. 
Analyses 15 and 16 represent the ordinary top water in the 
northern part of the Eastside Coalinga field. The exact position of 
these waters is not known, but from the higher primary salinity and 
concentration of No. 16 it is thought to be somewhat the deeper of 
the two. No. 18, from the Westside Coalinga field, is a water very 
similar in composition to the last but of exceptionally high con¬ 
centration. It is a sulphur water and therefore has probably been 
slightly influenced by the hydrocarbons, though the proportion of 
sulphate as compared with both carbonate and chloride is still very 
high. No. 19 represents an unusual top water whose exact horizon 
is unknown. Its concentration is very much lower than that of 
most waters of the west side and therefore the sparingly soluble bicar¬ 
bonates of calcium and magnesium, though present in small actual 
