48 
Colorado Experiment Station 
tides possess the power to retain the sulfates and chlorids as such, 
but they have little or no power to retain the carbonates. The sulfates 
and chlorids are retained near the surface and the sulfates in particular 
are first carried into the soil by descending' waters, are there seized 
upon by the soil particles and later may be brought to the surface again 
by ascending capillary currents to be left as efflorescences on the evap¬ 
oration of the solvent water. When there are no salts present in the 
soil to affect a transformation of the sodic carbonate, and no autflow- 
ing water to carry it away, it must become more and more abundant 
until it becomes strong enough to prohibit vegetation. . This is what 
has happened in the northern section of this valley. This I believe, to 
be the simple history of the 800 square miles of land included in this 
section. This is the reason why the artesian waters to a depth of 880 
feet at least are, for all practical purposes, a simple solution of sodic 
carbonate. It will be noticed that these waters carry but little silicic 
acid and still less of sulfates and chlorids. 
“WHITE” ALKALI REMAINS NEAR SURFACE—“BLACK” ALKALI 
GOES TO DEEPER STRATA 
The “white” and “black” alkalis, then, are formed simultaneously 
as primary products of the action of waters containing carbonic acid. 
There is a tendency for the “white alkali to be retained near the sur¬ 
face and for the “black alkali” to pass into the deeper-seated waters. 
If there be a deep under-ground movement of these waters out of the 
region, the “black alkali” goes out with them, if not, it must accumulate 
within the area. We have the former case in the one section and the 
latter in the other of the two sections that we have discussed. 
There are other ways that “white alkali” is formed. I have al¬ 
ready cited the production of sulfates by the oxidation of the sulfur 
in marcasite or other sulfids, principally of iron. While this is a widely 
distributed action it is not comparable in importance to the action of 
carbonated waters. 
CHANGES WITHIN THE SOIL DEPEND UPON SALTS PRESENT 
The changes that may take place in ordinary soils when solutions 
produced as above described, enter them will depend upon the salts 
in the soil and these changes will determine the character of the alkali 
of the locality. With us the general character is that of the sulfates. 
We have already seen that some sulfates are already present in the 
mountain waters, further that sulfates may be formed from the sulfur 
in the sulfids of iron which are widely distributed and also from other 
sulfids. Besides these sources there are already formed deposits of 
gypsum in certain geological horizons. This compound though not 
very soluble in water is a common constituent of our ground-waters. 
The manner in which this may act with sodic carbonate to form sodic 
