Alkali Deposits of Wyoming. — Read 165 
of the lakes yield pure mirabilite, which upon simple exposure 
to the air loses its water and becomes anhydrous sodium sul- 
phate. However, the distance of the region from the consum- 
ers of sodium sulphate and the consequent high freight tariff 
has so far ptevented their exploitation. 
The question as to their origin cannot be so easily disposed 
of. Of the various theories which have been propounded two 
alone seem to deserve consideration. Of these the first is that 
they are the result of the evaporation of the waters of uprising 
springs which are charped with the alkaline salts. The second 
is that they have resulted from the leaching of the surround- 
ing Mesozoic rocks. Let us first consider the latter. 
Assuming for the moment that these rocks are capable of 
supplying the amount of salts which we find in the depressions, 
let us investigate the conditions under which such deposits 
might be thus produced. In order to have a concrete case let 
us take the Union Pacific soda lakes which are situated about 
13 miles southwest of Laramie in Albany county. We have 
here four lakes with a total area of about sixty acres. The de- 
posit of soda was reported to be fifteen feet thick in the deep- 
est part of the depression and was assuredly not less than ten 
feet thick. Allowing for the thinning out at the edges it is safe 
to assume an average thickness over the entire area of two and 
a half feet. Upon this basis of computation we find that there 
are 300,000 tons of the deposit. From the analysis of an av- 
erage sample of this deposit published by Pemberton and 
Tucker in the Chemical A'czvs, vol. 68, p. 19, we find that it con- 
sists of 34.85^ of sodium sulphate, 1.16;'^ of sodium chloride, 
1.45^^ of calcium sulphate and 0.97^^ of magnesium sulphate, or 
a total of 38.43^' of alkaline salts ; and on this basis we have 
115,290 tons of these salts in the deposit. 
The surrounding strata are Ft. Benton, and it is reasonable 
to assume that the percolating waters from whose evaporation 
the deposits are supposed to have resulted would have approx- 
imately the composition of the water obtained from driven 
wells sunk in these strata. \Vc find that on the average such 
water contains a total of 50 grains per gallon of the above 
salts. The records of the Wyoming Agricultural Experiment 
Station show^ that the average yearly evaporation from a free 
water surface is 40 inches. Therefore from an area of 60 acres 
