Dissolved mineral matter in surface‐waters
The only unpublished comprehensive Geological Survey records of dissolved matter in surface‐waters are the results obtained in the study of the Colorado River and its tributaries since 1930. The records are mainly analyses of 10‐day composites of daily samples, although there are several analyses of spot‐samples from some streams in the basin and about 4000 single determinations of chloride or sulphate in daily samples. The need for a large number of analyses is shown by the fact that during the period 1925–35 the quantity of dissolved solids in 10‐day composites from the Colorado River at Grand Canyon ranged from 226 parts per million for June 11–20, 1929, to 1889 parts per million for. September 21–30, 1934. A series of analyses covering a whole year might be misleading. The weighted averages for the different years ranged from 491 parts per million for the year ending September 30, 1928, to 960 for the year ending September 30, 1934.