The Soil. 
17 
mica, magnetic oxid of iron, etc. I have not determined, by actual 
count, the grains of quartz and feldspar, but my judgment is that 
there is more quartz in the sands that I have separated from these 
soils than is indicated by the percentage given in the analysis 
quoted, viz., 40 per cent. It is to be expected that the mechanical 
composition of soils will vary from place to place, and yet the table 
shows a greater agreement than we would expect; the sample of 
loessial soil from Weld count} 7 and of loess from Larimer county 
being the only ones which show wide deviations in the percentage 
of any class of soil particles. Not only the mineralogical, but also 
the chemical examination of these soils, indicate a rather uniform 
composition, though the samples were taken from widely separated 
localities. By chemical analysis is here meant the analysis of the 
whole mass, a mass analysis, and not a soil analysis as it is made 
for agricultural purposes. 
§ 36. Dr. S. F. Emmons, writing of the loess in the “ Geology 
of the Denver Basin in Colorado,” says that it contains in all cases a 
large proportion of sand, separable by washing, whose grains are 
usually under a millimeter, but rarely less than a tenth of a milli¬ 
meter in diameter. The mechanical analyses of the loessial soils 
show 43 and 64 per cent, of the mass to have a diameter of less 
than five one hundredths of a millimeter. The mechanical analysis 
of this soil shows 47.40 per cent, of material, the clay not included, 
whose grains have a diameter of less than one tenth of a millimeter, 
and which differ from the coarser portions only in the degree of 
their comminution. The loessial soils given agree in having high 
percentages of fine sand and silt, and lower percentages of dust and 
clay than ordinary soils; but our results do not agree with Dr. 
Emmons’ observation that the grains of sand in loess are rarely less 
than one tenth of a millimeter in diameter. 
SIMILARITY OF THE PARTICLES AND COMPOSITION OF SOILS. 
§ 37. The fine sands are, in every case, much more angular 
than the coarser, due to the manner in which the water has effected 
their transportation, the larger having been rounded by rolling or 
by attrition while in suspension. The loessial soils show this char¬ 
acteristic as markedly as the other soils examined. There is so 
great a similarity in the mineralogical composition of our soils, 
though they vary in appearance, that it is a matter of some surprise 
that they should differ so extremely in properties. The chemical 
analysis of the soils, mass analysis, does not change this phase of 
the matter at all. The following analyses of samples taken from 
rather widely separated localities, may serve to illustrate this: 
