24 BULLETIN 61, V. S. DEPARTMENT OP AGKICULTUKE. 



The factors influencing absorption are the rate of movement of undergi-ound waters, 

 the concentration of solutions, the chemical nature of salines and salts, the distances 

 to be traversed to outlet if spring, or to sink if there is no surface outlet. In the case 

 of saline solutions retained locally the time factor is greatly increased and, conse- 

 quently, absorption may proceed to practical completion. The conditions in any 

 one case are so variable and the difficulty of definitely determining the quantities 

 involved so great that we can not determine the extent of absorption. Evidence 

 goes to show that potassium in some cases is almost completely retained. The com- 



Earison of undergi-ound waters with smiace waters and the comparison of soils from 

 umid and arid regions can, in a measure, be relied upon to show the character of 

 the changes. The two succeeding sections deal with these subjects. 



UNDERGROUND AND SURFACE WATERS. 



In Table XI (Appendix) are given a number of analyses of well and spring waters 

 from the Nevada experiment station records, obtained through the courtesy of S. C. 

 Dinsmore. Accompanying are two tables, Nos. XII and XIII (Appendix), giving 

 analyses of waters in Death Valley and Amargosa regions. The average ratios of 

 sodium to potassium are as follows: 



Ratio. 



Well and spring waters in western Nevada 43. 1 



Waters from Death Valley 47. 4 



Waters from the Amargosa 9.9 



The Truckee, Humboldt, and Weber Rivers 3. 6 



The basin lakes 20. 



Seepage originates in part from run-off waters. The absorption of potassium would 

 be indicated by a greater ratio of sodium to potassium in underground waters as com- 

 pared to the run-off waters. This is indicated by the above ratios. The ratio for the 

 basin lakes is intermediate between these for ground and surface waters. This ia 

 to be expected, since the lakes receive seepage as well as run-off waters. 



SOII/S OF HUMID AND ARID REGIONS. 



Clarke' gives the average analyses of a number of soils from humid and arid regions. 

 From these analyses the sodium-potassium ratio has been obtained and for purposes 

 of comparison the same ratio for the igneous rocks of the basin is given. 



Ratio of sodium to potassium in soils and rocks. 



Ratio of potassium in — ■ 



Humid soils 0. 39 



Arid soils 31 



Acid rocks ' 78 



Basic rocks 1. 50 



Mean, acid and basic 1. 14 



The figures obtained do not give a fair basis for comparison. In the case of the soils 

 the sodium and potassium are determined in the solutions obtained by decomposition 

 with hydrochloric acid. In the case of the analyses of the rocks the sodium and 

 potassium represent the total percentage of each in the rock. If we assume that the 

 insoluble residue obtained from the humid or arid soil would be of practically the same 

 constitution the ratios would be of some value in indicating absorption. The arid 

 soils show a greater proportion of potassium than the humid. If our assumption is 

 correct, this is due to absorption. It may also be due to differences in the degree of 

 decomposition. Comparing the soils with the rocks indicates the removal of sodium 

 at a much greater rate in the weathering process than potassium. If we compare the 

 percentage composition of the mean arid with the mean humid soil, we find the fol- 

 lowing interesting ratios: 



Ratio arid to humid percentages of constituents soluble in hydrochloric acid. 



Acid soluble: 



Soluble SiOa L7 



AI2O3 1. 8 



FezOa L8 



MgO 6. 2 



1 Bu]. No. 491 U. S. Geol. Survey, p. 4G7. 



