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 unit 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. 
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 
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 
Na 2 
KjO 
Total.. 
10.65 
1.880 
16.23 
2.018 
s 
CI 
COj 
S0 3 
P 2 5 
Total 
Acid type. 
Pounds 
constit- 
uent 
in 100 
pounds 
0.370 
.015 
.160 
.035 
.145 
725 
Pounds 
contrib- 
uted by 
weath- 
ering. 
0.370 
.015 
.160 
.035 
580 
Basic type. 
Pounds i Pounds 
constit- I contrib- 
uent ! uted by 
in 100 I weath- 
pounds. | ering. 
.068 
.326 
240 
.326 
.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 2 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. 
i Bui. No. 491, U. S. Geol. Survey, p. 467. 
1 Rocks, Rock Weathering, and Soils, Merrill, pp. 217-19; Mean of Percentages for K 2 and Na 2 0. 
20814—14- 
