56 
Colorado Experiment Station 
but the salts that are washed down into the low places were really 
formed in the high places, just as the ‘'black alkali”, told about in this 
bulletin was formed by the waters acting on the rocks of the mountains 
and has been carried down into the valley; and they would have all gone 
out of the valley with the w r ater if the water itself could have gotten 
out. In the southern section of the San Tuis valley the water has al¬ 
ways been able to get out and the “black alkali” has gone out with it, 
because the soil cannot hold the “black alkali” back as it can the 
“white alkali”. The same is true of the nitrates, the soil cannot hold 
them, they are easily washed out, and where the water runs out of a 
section it will carry both the “black alkali” and the nitrates out with 
it. This is the reason that we often find nitrates in waters. In our 
country this is true of water seeping out of the face of shale banks 
which have cultivated mesas or plateaus on top of them, or of water 
which may trickle along the surface of rocks, especially if it be the 
first portion that comes off, for nitrates may be forming on the sur¬ 
face of rocks; as well as on the surface of the land; but if these waters 
be sufficient to flow on they take the nitrates with them, if they evap¬ 
orate on the surface, they may leave the nitrates. These have nothing 
to do with our brown spots, though these nitrates are formed by the 
same little plants as the nitrates in the brown spots. The formation 
of these nitrates is going on near, or at, the surface only, and they do 
not come up from any considerable depth, nor are they stored up in 
deep beds like common salt. It is unusual to find such quantities as 
we have except in arid climate. It is only in a few places that these 
salts are produced rapidly enough to accumulate in soils as they have 
done in some of ours and then under very different conditions. The 
formation of nitrates is going on in every soil and even on the surface 
of many rocks so their occurrence in any place where there has not 
been water enough to wash them out may be expected. I have found 
small quantities on the face of sandstones and more in the little pockets 
made in the sandstone by the winds. In these cases the nitrates were 
all on the surface. They do not penetrate in such cases to any depth. 
I do not know how deep they may go. I have given, on a preceding 
page, an instance in which the surface soil and ground-water were very 
rich in nitrates, rich enough to kill cattle, but the water obtained from 
the shales at 280 feet did not contain a trace. These salts are not 
usually found in any quantities in deep water. Some very deep wells 
may yield water containing four or even seven parts per million but 
this is about the limit. 
In the cases that I have chosen to present the origin and character 
of our Colorado alkalis, we have not only the two big classes of “white”, 
and the “black” alkalis in a large area, but we also have scattered 
through both areas occurrences of the nitrates in injurious quantities. 
