52 
BULLETIN 61, U. S. DEPARTMENT OF AGRICULTURE. 
zation. From 18 to 35 feet a sulphate period followed, and this in turn was closed by 
the chloride period. Two periods of desiccation are indicated in the closing stages — 
the present one and one (recent geologically) at some unknown time before. 
The marginal bore also indicates an interruption in the desiccation. A passage 
from the trona to the sulphate period was followed by a trona period. The last trona 
period passes gradually into the chloride period, with possible indications of another 
interruption at 25 to 30 feet depth. More or less sedimentation marked this portion 
of the deposit. The final capping with a mud layer 13 feet thick closed the cycle of 
events at this point. 
The important question of what became of the residual mother liquor which must 
have covered the saline bed at the close of the last desiccation period has not been 
discussed. The suggestion by J. Walther, quoted by Clarke, 1 that residual bitterns 
might be absorbed by wind-blown sands, and by capillarity brought to the surface, 
wind eroded, and carried away, occurs as a plausible explanation. Undoubtedly 
some such action took place locally, but it could not have been on a sufficient scale to 
account for the removal of all of the mother liquors. The fact that the upper portion 
of the central bed contains a large proportion of sodium chloride and a brine lower 
in potassium content than the brine beneath suggests that the closing stages of desic- 
cation must have closely paralleled present conditions in Death Valley. Searles Lake, 
in passing through the last stages of desiccation, must have deposited sodium chloride, 
as well as other salts, over a much larger area than that occupied by the present cen- 
tral bed. The shallow lake of mother liquor occupying the central depression must 
have received periodic accessions of saline material from these marginal deposits. 
Continued over a long time the effect would be to build up a bed of saline material 
in which the content of potassium salts would not be conspicuous and which would 
contain the diluted original mother liquor absorbed in its interstices. Continual 
accession of salines from the margins would result in a top bed of saline material 
comparatively poor in potassium salts. This explanation appears to me to be the 
most reasonable. 
The central salt bed over practically the whole area of 12 square miles contains in 
its interstices a brine which, below the top bed of sodium chloride, is characterized 
by a relatively high content of potassium. According to Dolbear, the brine con- 
taining the high content of potassium salts is confined to a vertical horizon of some 
47 feet. Below this horizon the brines contain relatively less potassium salts. The 
following is an analysis of the rich brine taken from bore hole A7 on the N-S center 
line and just south of the center of the salt area: 
Analysis of brine from Searles Lake, expressed in percentages of the anhydrous residue. 
[Sample collestei by E. E. Free; aailysis by W. H. Ross, of tie Baraia of Soils.] 
Constituent. 
Per cent. 
Constituent. 
Per cent. 
Constituent. 
Per cent. 
Na 
33.57 
6.06 
.01 
None. 
None. 
None. 
Trace. 
Mn 
None. 
None. 
.012 
.003 
.023 
37.02 
.094 
I . 
0.004 
K 
Cu... . 
S0 4 
12.96 
Li 
A1 2 3 . 
C0 3 .. 
6.70 
Rb 
Fe 2 C>3 . 
PO4 
.30 
Ca 
Si0 2 ... 
N0 3 
NH< 
CI 
As0 3 
.083 
Mg 
Br 
B4O7 . 
3.00 
This is of the nature of a residual mother liquor. It consists of chlorides in greatest 
amount, sulphates, carbonates, practically no bicarbonates, and borates. It is con- 
spicuous by the presence of bromine, iodine, and arsenious oxide. The sodium- 
potassium ratio in this brine is 5.5. The average of 14 of the samples from the deep 
boring, omitting results upon crystals and Nos. 217 and 215, is 15.5. This would indi- 
cate that the water collected in the early stages of Searles was not unlike that of the 
present lakes in which the sodium-potassium ratio is 20. 
Supplementary analyses by A. R. Merz upon samples collected by E. E. Free are 
given in Table XXIX (Appendix). 
The brine body is contained in a mass of coarsely crystalline material, more or less 
honeycombed. The portion occupying the central mass of salt is richest in potassium 
ealts and borates below the upper salt crust of 18 feet thickness and above the 65- 
foot level. 
Bui. No. 491, U. S. Geol. Survey, p. 224. 
