Those 200 kilogrammes had been, therefore, dissolved in six mil-
lions kilogrs. of water, or, in other words, those soluble mineral
substances enter into the roots of plants in a state of 1 30,000 of
dilution in water; of course a very weak solution.

After these general foregoing remarks, I am now going to treat
upon these nourishing mineral substances in particular, as to their
origin, their importance for vegetable life, the extent to which
they ought to be present, and by what substances of commerce
they may be properly acquired. These substances may be
represented under the following heads:

1. Alkaline Salts (Salts of Potash and Soda,) and Solu-
ble Silicic Acid.

Origin.—Both of those substances which are on the head of
this paragraph, owe their origin to volcanic rocks, which are com-
posed of them as 1 have stated already in many places before —
By the disintegration of these rocks, they are partly liberated and
partly retained, according to the advancement of this chemical
process. Those rocks, among the volcanic or silicious, which are
before all others, rich in alkalies, are. at the same time, also those
which contain considerable quantities of clay, which, in combina-
tion with quartz, peroxyd of iron, &c, forms the last and remain-
ing product of the disintegration, inasmuch as they cannot be trans-
formed into other compounds. Wherever we find clay, whether
in mountainous regions, or as a component of soils, it derives its
origin from the disintegration of volcanic rocks; and as these vol-
canic rocks were such as contain at the same time considerable
quantities of alkalies, which were liberated contemporaneously
with the clay, by the process of disintegration, and inasmuch as
the clay exercises an immense attraction upon the former, we nev-
er find clay which does not contain a greater or smaller quantity
of alkaline salts, and therefore never a soil in which alkaline salts
could be entirely absent. Among the volcanic rocks which are
especially rich in clay and alkaline silicates, are to be named :
Granite, gneiss, syenite, mica-slate, basalt, lavas, and many oth-
ers. The manner in which the disintegration of them takes place,
showing a series of periods which are to be run through with be-
fore it is completed, is explained in a little pamphlet, of which
my former Assistant is the author, and which was published as his
inaugural thesis on his promotion to the grade of Doctor of Philoso-
phy. As a matter of general and especially of highly agricultu-
ral interest, I have no hesitation in quoting here a short extract of
his work:

"The rock of which 'the Kottenberg' in Germany is composed,
furnishing the material for experiment, belongs to those numerous
little basaltic cone mountains, which surround the large masses

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