i66 The American Geologist. ►September, i904. 
we would have 64,686,600 gallons exaporated yearly, leaving 
a solid residue of 231 tons. At this rate it would require 500 
years to create these deposits, assuming that evaporation takes 
place continuously and that none of the salts are removed. As 
a matter of fact the lakes are entirely dry during a good portion 
of the summer, when the evaporation is the greatest, and the 
milabilite then effervesces to a pulveulent mass which the pre- 
vailing west wind carries away in clouds. Probably not less 
than 2000 years would be required for the formation of these 
deposits under the conditions we have assumed. No records 
have been kept as to whether there have been any apparent 
changes in the extent of any of these deposits, and in the case 
of the one we have been considering the escape of seepage 
water from an irrigation canal which now passes just above the 
lake has caused the re-solution of all the salts, so that it now is 
a lake of brine and bids fair to remain so. However, I believe 
all observers of these deposits will agree with the statement 
that there seems to be no reason to believe that any of these 
deposits are accumulating at a rate much faster than that 
worked out above. Therefore we arrive at the conclusion that 
the vaporation of dilute solutions is sufificient to have caused 
these deposits and the assumption of uprising waters highly 
charged with these salts is not only unnecessary, but does not 
meet the conditions. Taking the deposits in general, the er- 
rors in the assumption in regard to the amount of water sup- 
plied and the strength of the solution would tend to counter- 
balance each other. 
The next point to be considered is the method of the con- 
centration. This may come from the seeping of the waters 
through the strata, finally emerging in the basin where they 
evaporate. Or the subsurface waters, evaporating over the 
entire drainage area, of which the basin is the lowest part, de- 
posit their load of salts on the surface. At the time of the 
spring rains the surface waters dissolve these salts and carry 
them into the basin to be later deposited by evaporation. Both ' 
methods find the salts in the strata in which the deposits occur. 
In the former, however, only the salts lying above the "lake" 
level could be brought in and in a comparatively short period 
the supply would be exhausted and no further deposition take 
place. In the latter, however, the salts might be brought up- 
