14 EB. W. Hiigard—Silt Analyses of Soils and Subsoils. 
As regards the modifying effect upon the extreme plastic 
roperties of the clay, the pulverulent ingredients obviously 
ivide into two chief classes, viz: 
1. The coarse portion, which increases the “ lightness” and 
porosity of the soul, sensibly in proportion to its percentage. 
2. The fine portion, which, while modifying the plastic prop- 
erties of the clay, yet renders the soil heavier in tillage than 
would be the case if it were absent, and the clay adherent to 
the coarse particles alone. 
Soils consisting mainly of very fine siliceous silt, with only a 
small percentage of clay, are among the very heaviest, work- 
ing “like putty,” clogging the plough when in the least degree 
too wet, and in drying, caking into clods of ‘“ hardpan.” 
Such being the case, it would seem that between the coarse 
part which lightens soils, and the fine silts which, like clay, 
render them heavier, there must be a neutral point—a degree 
of fineness which will not sensibly influence either the porosity 
or the compactness-of the soil. Odd as this conclusion appears, 
it seems nevertheless to be borne out by experience. 
In fingering the coarser silts, it at once becomes obvious that 
nothing above 1™™ hydr. value can tend to render a soil 
heavier; while it is equally manifest that the impalpable par- 
ticles belonging to the velocity of 0-25™™" cannot tend to lighten. 
n searching tentatively, by the summation of groups of phys- 
ical ingredients, for numbers that would satisfactorily express 
the estimated relative resistances to tillage of the soil analyzed, 
I found that such numbers would result from a summation of 
the three items lowest in the column, viz: the silts of 0°25, 
< 0°25, and clay. These are given under the head of “ Com- 
pactness” or “ Resistance to Tillage.” 
