8 
Colorado Experiment Station 
at hand. Concerning this easily available sulfur we need ask no ques¬ 
tions as to where it came from, it suffices that there are large quanti¬ 
ties of sulfides almost everywhere in our shales, especially if they have 
contained organic matter. The sulfides of iron, known as marcasite and 
pyrite, yield upon exposure to air, oxids of iron and sulfuric acid 
which may combine with lime and water to form gypsum or with soda 
to form sodic sulfate. This, under some conditions, is the easiest ex¬ 
planation for the presence of sodic sulfate in large quantities and it is, 
at least in part, the correct explanation. The occurrence of gypsum 
crystals in many of our shales owe their formation, in all probability, 
to the action of the sulfuric acid formed by the oxidation of these sul- 
fids of iron on lime compounds. There are immense quantities of 
gypsum along our foothills extending both north and south of us, and 
under the plains. As to the source of this sulfate of lime, it suffices 
in this case to acknowledge that it is there in very great quantities. 
Our knowledge of the source of the magnesium sulfate is not so 
clear. Lime is very frequently accompanied by magnesia, be it more 
or less in quantity. The felspars, which furnish lime and soda by 
their decomposition, also furnish a little magnesia and other minerals 
present in the rocks, also in the soil, contain magnesia, so there is no 
need of looking very far to find a source of this substance. Some 
of our limestones are strongly magnesian. The sulfate of magnesia 
is very easily soluble, as is also thq chlorid, so we would not expect to 
meet with these salts in our rocks. These salts do occur in extra¬ 
ordinarily large quantities in Stassfurt and elsewhere in Germany but 
the magnesian salts that occur in our alkalis have not the history that 
these Stassfurt salts have. Our salts have probably only started on 
their course to the ocean, while the Stassfurt salts have run this por¬ 
tion of their course and witnessed the passing of the ocean itself. The 
magnesian salts that we meet with in our rocks and minerals are sili¬ 
cates and carbonates; in our waters and alkalis they are the sulfates 
and chlorids. These salts are unquestionably formed in the soils by 
the interaction of the magnesian minerals and the sulfates and chlorids 
derived from the felspars through the action of carbonated water. 
The case of some deep-seated springs in the old metamorphic rocks 
may be different, but, the ground-water occurring sometimes within 
two feet of the surface, many of our shallow springs and even ar¬ 
tesian waters met within or above the Dakota sandstones will come 
under the statement made. 
In regard to the chlorids in general, I believe that I shall have to 
avail myself of an explanation that I recall having read somewhere 
which referred their formation to the primordial chemistry of our 
globe. The incompetency of this statement to explain anything is its 
commendation. We find chlorids in the old metamorphic rocks when 
