CLASSIFICATION OF THE OIL-FIELD WATERS. 
41 
industrial purposes and doubtless according to different standards of 
accuracy. They afford a good idea of the general character of the 
water, and in most of them the error is probably less than 5 per 
cent. 
In the tables of analyses the properties of reaction are stated first, 
as they are believed to be the most suggestive as well as the most 
* convenient basis for general comparison. The sulphate salinity 
ratio, or the percentage of rS0 4 in rS0 4 + rCl, is included under the 
properties of reaction, and in certain types of water the ratio of the 
values of carbonate and bicarbonate to the sulphate value is also 
given. Below the reaction properties is given the analysis itself, 
stated in radicles in parts per million; this is a summary of the basic 
data on which any form of interpretation must rest. The analysis 
is also stated in reacting values in percentages, a form that admits 
direct comparison of the chemical values of the radicles but does not 
express the actual amounts present or the concentration of the solu¬ 
tion. Finally, those analyses which were not made by the Geological 
Survey and which were originally stated in hypothetical combina¬ 
tions in grains per United States gallon are given in the tables in 
their original form also. To some readers this form of statement 
may be the most familiar, but for rational scientific study one of the 
other forms is strongly recommended. 
CLASSIFICATION OF THE OIL-FIELD WATERS. 
DISTRIBUTION AND SIGNIFICANCE OF THE CONSTITUENTS. 
Alkalies (sodium and 'potassium ).—In most of the analyses in this 
report the alkalies, sodium and potassium, have not been separated, 
and as their chemical properties and distribution are similar they 
will be considered together. The alkalies are by far the most abun¬ 
dant bases in the oil-field waters, and in many of the deeper waters 
they and their equivalent acid radicles constitute over 95 per cent 
of the total mineral content. In surface waters the alkalies are less 
prominent, but in waters from depths of more than 250 or 300 feet 
they usually predominate over the other bases. The waters associ¬ 
ated with the oil in the western parts of the Coalinga, Midway, and 
Sunset fields contain the alkalies almost to the exclusion of the other 
bases. 
The great predominance of alkalies over the other bases is a notable 
feature of the composition of the waters of the oil fields of the west 
side of San Joaquin Valley, for in most regions of sedimentary rocks 
the waters are characterized by a moderate to low proportion of alka¬ 
lies. The salts of the alkalies are highly soluble and therefore are 
never deposited from saturated solution, except in arid regions, 
where they tend to accumulate at the surface as deposits of “alkali,” 
