i68 The American Geologist. September, i904 
Where do the alkaUne salts come from? The spring the- 
ory has no answer to that question, beyond that they come 
from beneath. 
From a careful consideration of the evidence it would 
seem that both theories are right, and find their application 
in different instances. The southern edge of the valley of 
Rock creek, which that stream has cut in the crest of an anti- 
cline, is a ridge of hard Dakota beds. Near the crest of this 
ridge is an undrained depression containing one of these de- 
posits. We clearly can have no application of the first theory 
here, for with the exception of a low rim, the surface slopes 
away from the depression. On the other hand, we have nu- 
merous springs breaking out on all sides, all of them of water 
which is good enough to drink. These springs join into a 
small stream which flows into Rock creek. This seems clear- 
ly to be a case of a spring whose yearly flow is not equal to 
the yearly evaporation from its lake basin. In the case of 
the Union Pacific lakes we find a larger and deeper undrained 
depression, containing no deposit, a few miles to the north and 
another to the west. The absence of such deposits from these 
depressions is inexplicable by the theory of the leaching of the 
surrounding strata, since at least one of these depressions 
occurs in exactly the same strata. Therefore uprising waters 
from be neath must again be the probable source. 
On the other hand, it seems almost certain that the leach- 
ing of salts from the surrounding strata must have at least 
aided in the formation of the alkaline deposits. The presence 
of efflorescent crusts of alkali throughout the arid region 
shows that such salts are brought to the surface and surface 
drainage would naturally concentrate the alkali in the evapor- 
ating basin. Hence we arrive at the conclusion that both 
causes have operated, their relative importance differing in 
specific cases. 
As to the origin of the salts themselves there is almost no 
evidence to offer and without good evidence it is useless to 
construct a hypothesis. 
The position taken by Dr. W'. C. Knight in Bull. 49 of 
Wyoming Experiment Station, "Alkali Lakes and Deposits," 
seems to be clearly untenable. He assumes that the salts 
have been carried down mechanically by the sediments as they 
