SUMMARY. 
§ 108. The “alkali” salts in the soils and waters of Colorado 
are essentially mixtures of the sulfates of lime, magnesia and soda. 
§ 109. The soils of the eastern slope of the Rocky Mountains 
and of the plains lying to the east in Colorado, have in general a 
very similar composition, as shown by the composition of the soil 
mass. 
The mineralogical composition of these soils is very similar, 
the principal variation being in the ratio of the quantities of the 
minerals present. 
§ 110. The surface soils of this section of Colorado probably 
owe their mineral constituents to a common source, the schists and 
granites of the Colorado range. 
§ 111. The feldspar, orthoclase, an almost universal constitu¬ 
ent of our soils, serves as a source of potash and also of hydrous sili¬ 
cates under ordinary cultural conditions. 
§ 112. The readiness with which the chemical reactions take 
place and their character, as indicated by the salts present in the 
ground waters, probably have a direct and important bearing upon 
the fertility of the soil. The loessial soils of the plains agree with 
the ordinary prairie soils in the chemical composition of their mass 
and in the general results of the agricultural analysis, but not in 
the mechanical analysis. 
§ 113. The analyses of the whole soil mass and of the different 
portions of the fine earth, suggest important differences between the 
unchanged rock particles in the soil and the finer portions which 
have suffered change or are the products of alteration. 
§ 114. The aggregate amount of soluble salts per acre whose 
movement is effected by the water falling on or supplied to the surface, 
or by its evaporation from the surface, is large; we make it nine tons 
in one instance. The application of water, irrigation, may carry the 
soluble salts so deep into the soil that a long time may be required 
for them to come near to the surface again. 
§ 115. The chemical analyses give us no hint of the very great 
improvement which was effected in this soil by three, really four, years 
experimentation with it. Our question was one of conditions and 
not of composition, so far as its purely agricultural features were 
concerned. 
