8 HINTS ON SOILS AND FERTILIZERS 
fine. The coarser particles, being heavier, are 
soon deposited at some point further down 
the stream. A great number of years ago, 
scientists tell us (and they have sufficient 
proofs to verify their claims) that a huge 
glacier moved along this country from the 
north, and extended along the northern bor¬ 
der of the United States. These large ice 
sheets not only leveled the topography of our 
land, but they dragged along a great amount 
of soil from the north, and deposited it hun¬ 
dreds of miles south of its original position. 
Hence, we find many locations where the top 
soil is of different composition than the un¬ 
derlying subsoil. 
We have already learned that the soil con¬ 
tains mainly two classes of materials, humus 
and mineral elements. We have defined humus 
as decayed vegetable matter, such as the re¬ 
mains of plants that were not used by man, 
but left upon the soil. The elements of a 
mineral nature are just as essential to the 
welfare of the plant as the organic matter, or 
humus. We will discuss these mineral ele¬ 
ments from a chemical point of view in our 
next chapter, but we will now consider them 
briefly from a physical standpoint. 
When speaking of a soil, in general, we 
usually refer to it as either a sandy soil, a silt 
soil, as a clay soil, or as a loam of one of 
these soils. Now, just what do we mean when 
we say a soil is a sandy soil, or sandy loam, 
etc.? This classification is based upon the size 
of the soil particles that compose the soil. The 
sand particles are the largest classification of 
