KINDS OF SOILS. 153 
we may infer that lime is abundant in the soil. On the 
other hand, if asoil contains a large proportion of quartz 
pebbles, the legitimate inference is that it is of compara- 
tively poor quality. The term gravelly admits of various 
qualification. We may have a very gravelly or a mod- 
erately gravelly soil, and the coarse material may be char- 
acterized as a fine or coarse gravel, a slaty gravel, a 
granitic gravel, or a diorite gravel, according to its state 
of division or the character of the rock from which it was 
formed. 
But the closest description that can thus be given of a 
gravelly soil cannot convey a very precise notion of even 
its external qualities, much less of those properties upon 
which its fertility depends. 
Sandy Soils are those which visibly consist to a large 
degree, 90°|, or more, of sand, i. e. of small granular 
fragments of rock, no matter of what kind. Sand usually 
signifies grains of quartz; this mineral, from its hardness, 
withstanding the action of disintegrating agencies beyond 
any other. Considerable tracts of nearly pure and white 
quartz sand are not uncommon, and are characterized by 
obdurate barrenness. But in general, sandy soils are by no 
means free from other silicious minerals, especially feldspar 
and mica. When the sand is yellow or red in color, this fact 
is due to admixture of oxide or silicates of iron, and points 
with certainty to the presence of ferruginous minerals or 
their decomposition-products, which often give considera- 
ble fertility to the soil. 
Other varieties of sand are not uncommon. In New 
Jersey occur extensive deposits of so-called green sand, 
containing grains of a mineral, glauconite, to be hereafter 
noticed as a fertilizer. Lime sand, consisting of grains 
of carbonate of lime, is of frequent occurrence on the 
shores of coral islands or reefs. The term sandy-soil is 
obviously very indefinite, including nearly the extremes 
hed 
