Alkalis In Colorado 
47 
We have in this valley a series of strata of common origin, attain¬ 
ing a very considerable thickness, which formed the bed of a fresh¬ 
water lake. These strata abut against the metamorphic or igneous 
rocks which surrounded the lake and now surround the vallev. The 
valley abounds in alkalis of two kinds, the “white” and “black” alkali. 
The “white alkali” is very generally present but is probably nowhere a 
serious detriment. The “black alkali” is everywhere present, as would 
follow from our previous explanation, and is now being formed as one 
of the first products of the action of rain- and snow-water on the fels- 
pathic constituents of our rocks and soils; but, owing to its easy solu¬ 
bility and the inability of the soil to retain it, and also to the readiness 
with which it can be transformed into the sulfate, it has not accumu¬ 
lated in deleterious quantities except under special conditions. These 
special conditions in the case discussed are; First; that the sands and 
soils of the valley are identical in their mineralogical features with the 
rocks of the mountains; Second; that these conditions have been the 
same throughout the history of the valley; Third, that this portion of 
the valley has no sufficient drainage, owing to an old river fan or bar 
which divides the valley into two sections; Fourth, that there has been 
an approximate equilibrium between the water supply and the rate of 
evaporation during a very long period of time, just so long as this 
valley has existed. The result being that we have in the one section a 
comparatively simple phase of the alkali qusetion in which the products 
resulting from the action of rain-, snow- and phreatic waters on 
t e felspathic constituents of our rocks have been partly removed and 
those remaining only partially modified. For the sake of simplicity 
we can consider these products to be silicic acid, calcic, magnesic, and 
sodic carbonate with a little sodic sulfate and chlorid. Considering 
these to be the products of this action does no violence to the facts, as 
a reference to the analysis of the residue obtained from the Poudre 
River water will show. If anyone wishes to consider the results given 
in the analysis of the Rio Grande water as more typical, I call attention 
to the fact already pointed out that the difference is only a matter of 
aeration, and would support this by the results obtained by the exam¬ 
ination of the water of the Arkansas, taken above Canon City, which 
is just below the entrance to the Royal Gorge. 
The silicic acid would be removed from such a mixture bv flow¬ 
ing through a soil containing soluble salts with which it might com¬ 
bine, or even by sand grains themselves. The calcic and magnesic car¬ 
bonates can be precipitated by the simple removal of carbonic acid 
which holds them in solution. We find the most positive evidence of 
this deposition nearly everywhere in the soils of our State. This is 
the origin of the white, marly layer of soil encountered in the upper por¬ 
tion of our subsoil, sometimes as a veritable hard-pan. The soil par- 
