POTASH SALTS AND OTHER SALINES IN THE GEEAT BASIN EEGION. 51 



that crystallization must proceed at a comparatively slow rate under natm-al condi- 

 tions at the beginning of desiccation, and, as desiccation proceeds, the rate of crystal- 

 lization must increase to a maximima. Final desiccation of the mother liquors must 

 be a long drawn-out process, if at all completed. It is not impossible to expect that 

 at this stage of desiccation sedimentation by seolian action might proceed rapidly 

 enough to absorb the final mother liquor. The crystalline mass formed during the 

 final stages of desiccation would also absorb portions of the mother liquor at the end. 

 The saline content of a mud, assuming that it has absorbed a brine which is saturated 

 and at point of crystallization, has been calculated in the following: A wet mud 

 with a specific gravity of 2 and composed of mineral particles 2.6 would have a void 

 space of 37.4 per cent by voliune. If 1 cubic foot were filled with a brine of specific 

 gi-avity 1.25, the brine would weigh 29.3 pounds. Chatard's experiments on the 

 Owens Lake water showed a brine of 1.26 specific gravity at incipient crystallization; 

 and this contained 30.56 per cent by weight of salines. The brine filling 1 cubic foot 

 of the mud would contain approximately 9 pounds of salines. This would be equiva- 

 lent to 8.1 per cent of the weight of the dry mud.' Dry mud samples containing an 

 excess of 8.1 per cent of saline material would indicate satmated solution conditions 

 with some crystallization and deposits of salines ; less than 8 per cent it would be con- 

 cluded that the mud had captured an tmsaturated brine. 



If it is assumed that the mass of saline crystals would contain a void space of 30 

 per cent of its volume and the resulting mother liquor had a specific gravity of 1.3, 

 the weight of the brine solution contained in 1 cubic foot would be 24.4 pounds. If 

 we assume the specific gravity of the salines to be 1.9, the weight of the brine absorbed 

 would be 29.0 per cent of the weight of the dry saline material, or 22.4 per cent of 

 weight of brine and salt. This would not be sufficient to absorb all of the mother 

 liquors at the final stages of crystallization. 



Interpreting the chemical data obtained by the deep bore and the three surface 

 bores, and using the criteria which have been established, I have reached the con- 

 clusion below. 



The initial stages of Searles Lake were similar to Lake Lahontan. The lake at this 

 period might have been over 1,200 feet in depth, and there is no reason to suppose 

 that it was other than fresh. The drying up of the lake must have extended over a 

 great length of time. The first part of the record, 600 to 627 feet, indicates that the 

 lake had reached saturation and had begun to deposit salines. The brines at this 

 stage deposited salines low in carbonates, high in chlorides and sulphates, and notice- 

 ably high in potassium. Either sedimentation proceeded at a rapid rate or crystal- 

 lization must have been slow. The latter is more likely the case. At a depth of 

 586 to 596 feet the brine was diluted sufficiently to stop crystallization. The saline 

 content of this brine figures out as follows: 



Per cent. 



Potassium chloride 5. 48 



Sodium chloride 59. 15 



Sodium sulphate 29. 04 



Sodium carbonate 1. 31 



Sodium bicarbonate 2. 44 



During this stage carbonates were accumulating in the lake waters. Concentra- 

 tion of the water followed and salines were again deposited (575 to 580 feet; samples 

 Nos. 223 and 224). From 427 to 540 feet salines were steadily deposited and inclosed 

 by the sediments. The brine at this stage must have approximated in composition 

 evaporated Owens Lake water, for carbonates are found in increasing amounts. The 

 conditions must have approximated the trona period. During this period the rate 

 of crystallization exceeded sedimentation. The content of potassium is high. From 

 227 to 427 feet the record is lacking. At 227 feet conditions approaching the sul- 

 phate period are indicated. The salines are low in carbonates and high in sulphates 

 and chlorides. Potassium still remains high and amounts to 3.72 per cent of the 

 saline residue (sample 211). From 80 to 227 feet the record is lacking. 



The central bore of the Dolbear series indicates that at 65 to 79 feet depth the 

 trona period occurred, followed at 50 to 65 feet by the sodium chloride period, 

 and this was followed by a sulphate period at 35 to 50 feet. An interruption is indi- 

 cated here. More than likely a humid period diluted the lake and stopped crystalli- 



1 From experiments upon slime cakes formed by vacuum filtration, I have found that the densest por- 

 tion of a slime cake, formed under a pressure of 11 pounds per square inch, has a specific gravity of 1.84, 

 and a water content of 27.9 per cent. Using these figures and assuming a brine of 1.3 specific gravity and a 

 saliae content of 30 per cent by weight would give a saline content for the dried cake of 13 per cent. This 

 figure can be used comparatively with the one obtained by calculation. I am inclined to use the figure 

 obtained by the previous calculation, since the slime experiment does not take into accovmt the tune element 

 nor the greater pressures to which mud in the bottom of a lake would be subjected. 



