E. W. Hilgard—Silt Analyses of Soils and Subsoiis. 15 
Similarly, numbers satisfactorily expressing the relative 
“Openness” result from the summation of the coarser ingredi- 
ents, down to 1™™ inclusive. These numbers are given oppo- 
site to the heading “ Porosity.” 
But either series becomes quite unsatisfactory, so soon as the 
silt corresponding to 05"™ is added either way; except, of 
course, where its percentage is too small to influence either 
sum very seriously. 
course these can only be approximations, it being espe- 
cially obvious that sand of 64 and 32™ must exert a much 
greater influence toward rendering a soil “open,” than silts of 
1 or 2™™; which are, nevertheless, accounted for as equal in 
effect, in the above summation. Yet even here there are 
rmed a “woolly” condition of looseness. It is therefore 
quite intelligible that, within certain limits, “coarse silt” 
should exert a “lightening” influence equal to that of “ coarse 
sand,” which is apt to pack quite closely. 
It may be asked, What would be the character of a soil 
consisting exclusively of the silt of 0°57, claimed to be sen- 
y 
soils? TI reply that, judging from the small quantities of 
agg. tes will ] 
sist of fortcles of equal hydraulic value, the natural tendency 
being for small particles to fill up the interstices left between 
larger ones, which cannot attain close contact between them- 
selves alone,* Moreover, in view of this inevitable formation 
* There is a sensible difference, in this respect, between materials much rounded 
_Water-worn, rains are still “sharp.” 
more difficult to separate in the churn elutriator, and re-coalesce 
