170 Causes of Fertility or Barrenness of Soils. 
soils, such as pure clays and sands. In all other instances, the 
analysis presented the existence, in varying proportions, of those 
substances supposed to induce fertility, equally in tlie barren as 
the fertile soil. The proportion of the various ingredients was 
next proposed as the sign of quality ; but researches into the 
amount of inorganic matter abstracted by each crop liave de- 
monstrated that soils of a mixed character contain abundant 
supplies of mineral food for numerous crops. It is probable that 
fertility depends, more upon the peculiar condition of the saline 
matters, than their actual presence or absence in a soil ; thus for 
example, we can imagine a clay soil, so full of water, that the 
air could not penetrate, and act upon the various salts, which, 
though of the right kind, might be in an insoluble and therefore 
useless condition ; but the same soil, subjected to thorough 
drainage, and pulverization (physical change of its particles), 
might become very fertile, owing to the reviving influence of 
atmospheric action, and the increased temperature which would 
follow removal of the water, &c. It is for these reasons that 
fertility often appears to depend more upon physical than 
chemical causes, whereas the two are intimately combined : for 
instance, a pure sand may be physically in the best possible 
state, porous, warm, capable of retaining moisture, and yet totally 
barren from the absence of those chemical compounds upon 
which the plant feeds ; and, vice versa, the storehouse may be full, 
nature's laboratory may contain abundance, and yet the physical 
condition may be such, as to prevent those farther changes re- 
quisite, before the food can be fit for use. Before entering more 
particularly into an examination of the physical properties of 
soils, it may be as well to glance very briefly at their origin. 
Soils are derived from three sources : First, from the decompo- 
sition of the rock on which they rest. Secondly, from the de- 
composition of a drift formation, to which, in earlier days of 
geologic knowledge, the term Diluvium was applied, on account 
of their supposed formation by the Noachian Deluge ; a view 
long since found untenable, and the name has given place to that 
of erratic tertiaries, because most of these beds seem referrible 
to a period posterior to the tertiary deposit. Various theories 
have been broached to explain their formation ; the most 
plausible refer them to a period immediately preceding the 
present, when the earth was about to emerge from its watery 
covering, and when the natural elevations of its surface would 
cause mighty currents, carrying away in their course vast quan- 
tities of matter from the higher points, depositing tliem according 
to gravity at nearer or greater distances from the parent bed : the 
heavy matters would be deposited first, afterwards the finer and 
lighter ones. The direction of these currents seems to have been 
