ECONOMICAL GEOLOGY. 
163 
materials removed and deposited in new situations, by the agency of water 
or ice, and so, as consisting of drift or alluvium or colluvium ; the first 
being a collection of the unsorted and confusedly commingled debris 
of disintegrated rocks ; the second, of the finer materials, sorted and 
more or less arranged, — stratified, in quiet or gently moving currents ; 
and the last a mixture of these fine sediments with more or less coarse 
gravel and fragments of rock. From what has been previously said, it 
is evident that these transported soils correspond geologically to the 
Quaternary rocks and are found almost exclusively in the east, while the 
sedentary are exclusively middle and western, and consist of decom- 
posed granites, gneisses, schists, slates, <fec. 
Of course the soils will vary in chemical composition, and in fertility 
according to the character of the rock from which they were derived ; 
so that a geological map would furnish the basis of a soil map. 
The principal mineral components of soil in general, are Silica , Alu- 
mina , Potassa , Soda, Lime , Magnesia, Iron • but besides these, there 
must be present, to make a productive soil, a small per centage of com 
pounds containing several other elements, phosphorus, sulphur, chlorine, 
nitrogen and carbon. And these components, except the last two, can 
only be derived from the rocks. And since all rocks are derived from 
granites originally, the granites must contain whatever is found in any 
soil. The chief elements of the granites are quartz, felspar, mica, horn- 
blende. These minerals vary much in composition ; thus there are several 
species of felspar, which is essentially" a silicate of Alumina and an 
alkali, this alkali being potash or soda, or both in different proportions, 
and lime being present in some of them. And while mica is normally 
a silicate of alumina with potash and magnesia, some species also contain 
soda and iron. And so there is a great variety’- of hornblendes, which are 
mainly silicates of magnesia and lime, with generally alumina and iron, 
and in some species also soda or potash, or both. 
Quartz or silica is the predominant element in granites and most other 
rocks, and also of soils. Alumina, the base of clay, is the next in order 
■of abundance in rocks, and also in soils ; this is derived chiefly from the 
decomposition of felspar and mica. Potash and soda are also derived 
chiefly from the felspars, but in part also from mica, and to a small extent, 
from hornblende. The lime comes mainly from hornblende, but a 
little is contributed by some kinds of felspar. The hornblendes and 
some of the micas furnish magnesia. And hornblende is also the chief 
source of the iron of soils, but some of the micas furnish it also. There 
ure also many other minerals, some of them even occurring as rock 
masses, which sometimes furnish these diflerent soil elements in abun- 
