Winter precipitation is defined as rain, dry fallout, and bulk precipitation—the last being a mixture of the other two. The division of winter precipitation into phases is based on collection procedures. Each phase shows distinctive characteristics of chemical composition. Rain displays the strong influence of the nearby Pacific Ocean and San Francisco Bay. Dry fallout, collected between rains, shows strong effects from locally derived materials in the atmosphere. Bulk precipitation shows, in chemical composition, the expected blending of the two environmental influences and is about 4 to nearly 10 times higher in mineral concentration than rainwater is. Bulk precipitation is considered the geochemically significant phase that should be used in studies relating contributions of atmospheric salts to surface‐ and groundwater supplies, to weathering, and to the nourishment of growing plants. Comparison with published data indicates that, wherever sampled, bulk precipitation contains more dissolved mineral content than rainwater does. Detailed comparisons, however, are not feasible because of widely differing procedures in sampling and analysis used in various studies. Increasing attention should be given to minor constituents in precipitation, as well as recognition of the several phases of precipitation.

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trons for the dark-adapted eye of a careful observer to detect this phenomenon. It remains for future research to characterize the relationships of flash brightness and shape with charge, momentum, and trajectory.

Nitrogen compounds in natural water are significant in public health, agriculture, industry, and geochemistry. The many sources of nitrogen compounds and the deep involvement of nitrogen in the life processes of organisms makes the study of such compounds difficult. The sources include natural aerosols, precipitation, fixation by micro‐organisms in soil and water, decaying organic matter, and animal and industrial wastes, as well as probably undiscovered sources in consolidated and unconsolidated rocks. Nitrogen compounds are both oxidized and reduced by organisms. Some nitrogen compounds are adsorbed on clay. The theoretical end product in water and the compound probably most often determined is NO3−1. The concentration of nitregen compounds ranges from 0.0 to >100 ppm (parts per million) in surface water and from 0.0 to >1000 ppm in groundwater. Seasonal fluctuations occur. Much further research is needed, including improvements in methods of analysis, further investigation of sources, and detailed study of the nitrogen cycle in small drainage basins. (Key words: Geochemistry; quality of water.)

Factor apalysis is applied to results of chemical analyses of 103 water samples from wells in the Upper and Middle Mojave River valley, San Bernardino County, California. Chemical analyses showed that there are three principal chemical types of water, calcium bicarbonate, sodium sulfate, and sodium chloride, as well as many mixtures of the three. Data were studied by factor analysis to learn the relative importance of each principal ion in determining the variations among the samples, and to examine the possibility of chemical equilibrium between aqueous and solid phases in the aquifers.Most of the covariance in the system may be accounted for by variances of Ca +•, Mg +•, Na +•, SO• -•, and C1-L There is almost identical loading on the constituents Na +• and C1-L The variance in chemical composition of the hydrochemical system is governed largely by sources of sodium chloride. None of the components is controlled by equilibrium between ions in the water and minerals in the aquifers. Concentrations of NO8 -• and F -• vary independently of other constituents. Geographic distribution of statistical loadings of the principal constituents at individual wells does not reveal sources of the constituents, which must be deduced from geologic and hydrologic evidence. Factor analysis, however, furnished the critical information on chemical relationships basic to the deduction. (GEOLOGIC AND HYDROLOGIC ENVIRONblENT The Upper Mojave River valley occupies about 650 square miles near the southwestern apex of the Mojave Desert (Figure 1) and is defined [Bader et al., 1958] as that part of the river valley extending from the base of the San Bernardino Mountains to the river narrows near Victorville, about 20 miles downstream. In this area, most water samples are distinct as to chemical type: calcium bicarbonate, sodium sulfate, or sodium chloride. About 400 square miles of the Middle Mojave River valley [Page et al., 1960] adjacent to the upper valley is included in the present study. There the waters are mostly varied mixtures of the three original chemical types. The Mojave River is formed by the junction of the West Fork Mojave River and Deep Creek. These streams rise on the north side of the San Bernardino Mountains, near Cajon Pass. The rocks of the mountains are mostly metamorphic and igneous [Dibblee, 1957], but toward the west include sedimentary types. The metamorphic terrane is a complex of gneiss, biotite schist, mica-quartz-albite schist, quartzite, and marble of Precambrian (?) age intruded by quartz diorite, granodiorite, and diorite of Mesozoic age or older. Some of the schist is pyritic (L. C. DutcheL oral communication, 1965). The igneous terrane consists mostly of biotite quartz monzonite but includes granite and granodiorite. It is probably of late Jurassic or early Cretaceous age, but in part may be older. The sedimentary rocks in and north of the drainage basin of West Fork Mojave River are continental deposits of sandstone, siltstone, and shale, which locally include some conglomerate, limestone, dolomite, ...