MICHIGAN ACADEMY OF SCIENCE. 
57 
can be called at this time, have made clear that practically every soil 
contains some at least of every kind of rock forming mineral. To these 
are added the products of organized life and the degradation and de- 
composition products resulting from them. Mineralogical investiga- 
tions showing the large numbers and variety of minerals present in every 
soil are equalled in importance by some recent chemical investigations 
which show an amazing variety of elements. In each of a series of 
soils from different sections of the United States, east of the Mississippi, 
there has been found in detectable and generally in estimable quanti- 
ties nearly every known element. And in the organic residues of ordi- 
nary soils which have been under cultivation, there have now been 
isolated and identified some twenty definite chemical individuals, of at 
least eight different types. 
Water and winds are constantly transporting soil material from 
place to place, so that in all cases the soil is far more heterogeneous 
than any rock. Aside from the heterogeneity of soils, the results of 
these activities of water and winds are easily recognized. Throughout 
the humid areas of the world it is a general rule that the surface soil 
is lighter in texture than the subsoil, though the former is derived 
from the latter, the smaller particles being more easily removable. In 
arid regions this rule will not apply, for special conditions determine 
soil formation in each and every area. Within any given area of the 
soil itself we recognize that the particles must be moving continually. 
The sinking of heavy objects into the soil is an evidence of this. We 
know that earth worms, burrowing animals and like transporting 
agencies are of great importance, but more than these is the importance 
of the alternate wetting and drying of the soils incident to weather 
changes* which wetting and drying is accompanied by expansions and 
shrinkages which do not exactly balance one another and which must 
in consequence be accompanied by movements of the individual particles 
of the soil, and by a considerable mixing and transporting of these 
particles among one another. From the very nature of the case we 
know that living organisms within the soil must be moving, and all the 
biological factors are continually in process of change. 
The water falling upon the earth makes possible the use of the ma- 
terial as a medium for plant growth by bringing in solution to the 
absorptive tissues of the roots, the mineral elements which we all now 
recognize as essential to the growth of plant and animal. In falling 
as rain, a portion of this water fails to enter the earth by remaining 
in the air as vapor. Another portion runs off from the surface, while 
the remainder enters the soil and percolates through it, mainly as the 
result of gravitational forces and through the larger soil openings. 
Some of this water goes into the soil, seeps through and appears at the 
surface in the form of springs and wells and passes off into the drain- 
age of the area. This water, dependent upon the character of the 
soil, the length of its passage and other obvious factors, dissolves from 
the soil some of the mineral matter, and so we find all our creeks and 
rivers diluted soil solutions of varying composition and concentration. 
As the surface of the soil dries there is developed there a capillary drag 
or pull, and some of the water which has entered the soil reascends 
to the surface, generally more slowly than it penetrated into it, passing- 
in this case over the surface of the soil grains as films, being long in 
