POTASH SALTS AND OTHER SALINES IN THE GREAT BASIN REGION. 



17 



The results given are for humid conditions. We have no examples of a similar 

 nature for arid conditions. A rough approximation may be made from the comparison 

 of soils of arid regions with those of humid. Clarke ' gives average analyses of a number 

 of soils for both climatic conditions. From these we can obtain the ratio of one 

 constituent in the average of soils from arid regions to the same constituent in average 

 of soils from humid regions. These ratios are given in the foregoing table. If we 

 assume that the proportional loss of a constituent from rocks in arid regions is the. 

 product of the proportional loss in humid regions and the reciprocal of the ratio, the 

 results in second column of above table are obtained. No high degree of accuracy 

 can be vouched for these results. 



The following table has been calculated from the tables immediately preceding, 

 and gives, perhaps, a better idea of the measure of igneous rock decomposition and the 

 liberation of soluble constituents. The imit is taken as 100 pounds and only the more 

 important bases and acids have been calculated. The acid constituents, with the 

 exception of phosphoric acid, have been assumed to be entirely liberated. 



Contribution from 100 pounds of original rock. 





Acid type. 



Basic type. 





Acid type. 



Basic type. 





Pounds 

 constit- 

 uent 

 in 100 

 pounds. 



Poimds 

 contrib- 

 uted by 

 weath- 

 ering. 



Pounds 

 constit- 

 uent 

 in 100 

 pounds. 



Pounds 

 contrib- 

 uted by 

 weath- 

 ering. 



Pounds 

 constit- 

 uent 

 in 100 

 pounds 



Pounds 

 contrib- 

 uted by 

 weath- 

 ering. 



Pounds 

 constit- 

 uent 

 in 100 

 pounds. 



Pounds 

 contrib- 

 uted by 

 weath- 

 ering. 



MgO 



CaO 



NasO 



10.50 

 2.15 

 3.35 

 4.10 



0.156 

 .114 

 .831 

 .779 



4.52 

 6.33 

 3.29 

 2.09 



0.470 

 .335 

 .816 

 .397 



S.. 



0.370 

 .015 

 .160 

 .035 

 .145 



0.370 

 .015 

 .160 

 .035 



0. 066 0. 066 



CI 



CO2 



.068 

 .326 



.068 

 .326 



K2O 



SO3 







P2O- 



.240 







10.65 



1.880 



16.23 



2.018 



TotaL. 







Total 



.725 



.580 





.460 









SEDIMENTARY ROCKS. 



The pre-Tertiary sedimentaries of the basin region are not important sources of 

 saline material. Limestones are abundant and contribute to the lime compounds 

 associated with salines. The gypsum deposits of the Triassic are and have been an 

 important source of this compound. From Table X (Appendix), giving the average 

 analyses of Great Basin rocks, it is seen that limestones contain 0.51 per cent alkalies. 

 Merrill ^ shows that for weathering under humid conditions a limestone loses 63 per cent 

 of the alkalies. If we take one-third of this as representing the conditions for an arid 

 climate, we would have 21 per cent of 0.51, or about one-tenth of a pound of alkali 

 per 100 pounds of fresh rock. The slates and quartzites contain small quantities of 

 alkalies, but weather much less rapidly than either igneous or calcareous rocks. By 

 their decomposition small amounts of bases are contributed to salines, but, on the 

 whole, we must consider them far less important as a source of salines than other rocks. 



The Tertiary lake beds constitute one of the most important sources of saline materials 

 outside of the igneous rocks. They consist of limestones, shales, diatomaceous beds, 

 slates, and sandstones. Interbedded and often commingled are salines of which, 

 common salt, sodium sulphate, gypsum, and boric minerals predominate. The dis- 

 integration of these beds liberates saline material, while the decomposition of the 

 residual portion contributes an additional amount. As these beds are comparatively 

 soft, they would erode rapidly, and, no doubt, in late Tertiary and Quaternary times 

 they contributed a large proportion of the detrital filling of the present basins. The 

 table following, showing partial analyses of lake-bed material, will give some idea of 

 its chemical nature. 



1 Bui. No. 491, U. S. Geol. Survey, p. 467. 



2 Rocks, Kock Weathering, and Soils, Merrill, pp. 217-19; Mean of Percentages for K2O and Na20. 



20814—14- 



