POTASH SALTS AND OTHER SALINES IN THE GREAT BASIN REGION. 41 



about 12 feet thick and thinning out on the edges to 6.5 feet. Almost complete 

 desiccation must have marked the end of the period. 



5. A greater rainfall changed conditions, and a shallow lake formed. More or less 

 silting and deposition of clay sealed over the salt beds. Desiccation succeeded this 

 comparatively brief interval, and the lake shrunk and deposited a thin layer of salt 

 over a restricted area (2.5 feet of salt in boring No. 12) at a depth of 18 feet from the 

 present surface. 



6. A greater rainfall produced a shallow lake, perhaps not more than 10 or 15 feet 

 deep. This lake gradually silted up and slowly evaporated until the present condi- 

 tion was reached. 



The lake is dry for perhaps the greater part of the year, and only in the wettest years 

 is water present on the surface. The silting up of the lake must have been accom- 

 plished in a large degree by seolian action. The presence of a recent volcanic cone 

 on the western edge of the marsh indicates one of the sources, at least, of the material 

 which filled the lake. The mass of silts and muds filling the lake basin contains a 

 saturated brine. 



A chemical examination of the brine indicates the nature of the salines accumulated 

 in this lake bed. From the work previously cited the following table is taken: 



Analyses of composite samples of brines — Silver Peak Marsh} 

 [Parts per 100,000.] 



Constituent. 



1 



2 



3 



4 



9 



10 



CI 



59.37 

 .88 

 .01 



36.12 



2.71 



.67 



.24 



I 



59.01 



1.70 



.01 



36.54 



2.26 



.36 



.11 



.01 



57.35 



1.30 



.83 



32.87 

 3.12 

 1.92 

 2.49 



.12 



60.11 



.99 



.01 



34.65 



2.95 



1.25 



.04 



59.16 



1.09 



.29 



34.38 



3.69 



.84 



.48 



.07 



58.32 



SO4 



1.61 



COs 



.69 



Na 



34.37 



K 



3.11 



Ca 



1.29 



Mg 



.50 



Fe.... . 





Al - - - 



.11 



SiOa 



on evaporation, parts per 



J 







Total solids 

 100,000 



100. 00 



278. 76 



100. 00 

 264.03 



100. 00 



48.82 



100. 00 

 233.44 



100. 00 

 57.60 



100. 00 

 39.33 







1 W. B. Van Winkle, analyst. Table recalculated from Bui No. 530R, U. S. Geological Survey. 

 Composite of samples from boring No. 3 at 15.5 feet and from No. 6 at 21 and 40 feet. 

 Composite of samples from boring No. 11 at 27 and 35 feet and from No. 12 at 10, 20, and 27 feet. 

 Composite of samples from boring No. 13 at 16, 31.5, and 40 feet. 

 Composite of samples from boring No. 14 at 11 and 17 feet. 

 Water from boring No. 1 at 6 feet, collected June 1, 1912. 

 Water from boring No. 1 at 27 feet, collected June 4, 1912. 



The order of the ions is: 



Na 35.14 



K 2.94 



Ca 1.05 



Mg 64 



CI 58.86 



SO4 1.26 



CO3 30 



SiO, , 06 



Carbonates and sulphates are inconspicuous in amount. The brines consist almost 

 wholly of sodium and potassium chlorides. They are practically saturated. The 

 ratio of sodium to potassium is 11.9. The brines at depth show a somewhat smaller 

 content of potassium than the composite samples. The average is 0.69 per cent of the 

 total solids.' Dole gives the analyses of four spring waters tributary to the basin; 

 two are from hot springs and two from cold. These waters have a chemical content 

 very much the same as the brines. They are slightly higher in sulphate radical and 

 average slightly higher in potash content. The sodium-potassium ratio is 10.8. 



Certain interesting observations were made upon the brines. In boring No. 12 

 the brine encountered at 8.5 to 10 feet rose to 1.8 feet (head of 7.45 feet); those at 

 18 to 20.5 feet rose to 7.5 feet (head of 11.75 feet); those at 22 to 35 feet rose to 8 feet 

 (head of 20.5 feet). A similar condition was noted in bore No. 11 and most of the 

 other bores which penetrated the brine body. These observations indicate the effect 

 of pressure no doubt caused by the elevation of the water plane in the ground water 

 outside the main silt area. 



The source of the salines has been discussed by Spurr.^ He reaches the conclusion 

 that the weak brines discharged by springs around the marsh are the source. Dole 



1 Bui. No. 530R, U. S. Geological Survey, p. 14. 



2 Professional Paper No. 55, U. S. Geological Survey. 



