42 BULLETIN 61, U. S. DEPARTMENT OF AGEICULTUEE. 
suggests that these springs may derive their salines from the marsh itself. Both Dole 
and Spun state that the leaching of the Tertiary stratified rocks which are present in 
the basin in extensive areas accou nts for much of the saline residue. If Dole's estimate 
of the quantity of salt. 15.000,000 tons, be taken, and the area of the basin considered, 
1.9 pounds per square foot of the basin surface would account for this quantity. It 
would not be unreasonable to expect this to be derived from the erosion of the Tertiary 
sedimentaries and volcanice, especially when we consider the great amount of erosion 
which has taken place in Clayton Valley. _ Spurr points out. however, the conspicuous 
absence of borates in the salines of the Silver Peak Marsh and their presence in the 
neighboring playa to the west — Fish Lake Valley. In both localities Tertiary sedi- 
ments are common. He rightly reasons that if these sedimentaries were responsible 
for the salines, borates would also be present in the Silver Peak salines. His con- 
clusion that the salines of the Silver Peak Marsh are derived from hot springs at the 
edge of the playa would not account for the absence of borates at depth. Three 
possible hypotheses suggest themselves: The absence of the "borate member" in the 
Tertiary sedimentaries of the Silver Peak Basin and its presence in the Tertiary 
sedimentaries tributary to Fish Lake Valley; deeper borings in the Silver Peak Marsh 
might reveal borates : the volcanic activity in the Silver Peak Marsh was not character- 
ized by emanations of boric compounds. 
The source of the borate compounds in Tertiary sedimentaries is generally conceded 
to be due to contemporaneous vulcanism. This must have been local and would 
result in localization of boraciferous strata in the Tertiary series. This leads me to 
favor the first hypothesis. I do not, however, consider the question settled, and 
further data must be obtained before it can be. 
I am inclined to the view that the major part of the salines were derived from the 
erosion of the rocks of the basin; that possibly recent volcanic activity was respon- 
sible for a part also; and that much of the present surface accumulation is due to the 
springs and seepage water. 
Dole estimates the quantity of salt in the Silver Peak Marsh as 15,000.000 tons 
within the first 40 feet. The deposit has commercial possibilities for the production 
of salt. The average of the analyses upon the four brine composites shows 2.76 per 
cent potassium in the anhydrous residue. This is equivalent to 5.2 per cent potassium 
chloride. It is doubtful whether this is high enough to warrant the attempt to separate 
the potassium salt. The association of the brine with compact muds would prevent 
it from freely flowing to a bore hole. There would be, therefore, some difficulty in 
obtaining sufficient brine from a few bore holes to supply evaporating vats. The 
small amount of carbonate and sulphate would render the problem of the separation 
of the sodium and potassium chlorides comparatively simple. The production of 
sodium chloride with a by-product rich in potassium chloride is not beyond the possi- 
bilities of commercial exploitation. 
Conditions in Rhodes, Teels (PL I, fig. 1), Fish Lake Valley, and Saline Valley 
are very much the same as in Silver Peak Marsh. L T ndoubtedly shallow lakes occu- 
pied each of these basins, and the filling-in process and the desiccation of the lakes 
must have been similar. Unfortunately the results of systematic boring are not obtain- 
able. No doubt each of these presents individual characteristics and differs in some 
details from the example described. The most marked difference is in the presence 
of borates. 
In Fish Lake Valley, Turner states that there are four playa deposits, all of which 
have been worked for borax. Analyses by G. Steiger show in one case chloride, 
sulphate, carbonate, and borate of sodium. In another, sulphates and borates of 
calcium and sodium. No mention is made of potassium in the analyses. 1 
< The conditions at Rhodes Marsh have been described by LeConte. 2 His observa- 
tions are summarized below. 
The central area is occupied by a salt crust consisting of almost pure sodium chloride. 
About the salt area and below the surface soil is a comparatively thick bed of sodium sul- 
phate. Sodium carbonate occurs in soft crusts 2 or 3 inches thick, but is not general. 
Borax and ulexite also occur. The ulexite is in the form of nodules imbedded in wet, 
stiff clay in the semicircular area surrounding the central salt area on the north, north- 
west, and northeast. The borax occurs on the west, southwest, and southeast of the 
central salt area. It is in a moist, stiff clay which is full of the transparent crystals. It 
also occurs as a crust from 1 to 3 inches thick. This crust renews itself. The localization 
of the salts is attributed to the action of springs, and the concentration of the pure 
sodium chloride in the lowest part of the playa is attributed to the leaching of this 
compound by surface waters. It is evident from the description that the salines in 
the marsh are much more complex than those in the Silver Peak area. The regional 
rocks are similar to those about Silver Peak. The playa is of special interest in that 
1 Professional Paper No. 55, U. S. Geol. Survey, pp. 158, 159, Spurr. 
* Third Annual Report State Mineralogist of California, 1883. 
