THE CHEMISTRY OF SOILS AND MANURES. 
THE CHEMISTRY OE SOILS AND MANURES. 
By Dk. A. VOELCKER, Professor of Chemistry ra the Royal Agricultural College, Cirencester. 
ON THE FORMATION OF SOILS CHEMCAI CAUSES. 
7l\|OTWITHSTANDING a general similarity in the composition of arable soils, the character and 
Ai appearance of many soils in every country present striking differences, which cannot fail to 
attract the attention of even a superficial observer. The forms and proportions in which the chemical 
elements usually constituting soils are mixed together, in different localities, explain in some measure, 
though by no means fully, the various appearances and agricultural capabilities which they possess. 
These forms and proportions themselves depend on the causes and circumstances under which they 
originated. We must therefore consider the mode of formation of soils as a third or primary cause of 
their diversity. 
Hence arise the following questions — How are soils formed in general ? Has there been one 
cause at work, or have several conduced in producing different soils ? What relation does the surface 
soil bear to the subsoil ? Does the surface soil always present the same relation to the subsoil or rock 
on which it rests ? or, in other words, Does an invariable law connect the surface and substrata ? 
These are questions, a correct answer to which will enable us not only better to distinguish soils 
from each other, and to classify them according to then - more prominent characteristics, but which 
will also indicate whether a soil possesses in itself the means of improvement, and suggest the means 
bj' which it may probably be permanently improved at the least cost. We shall therefore endeavour 
to give a brief sketch of the origin and formation of soils. 
The manner in which some soils are formed will not be long doubted by any one who has observed 
the appearance of large rocky masses, the clefts and crevices they present, the bare surface of their 
smoother and harder parts ; the growth of mosses and smaller plants on the more softened portions ; 
the accumulations of gravel, smaller fragments of minerals, and fine mud, with then- luxuriant vege- 
tation at the foot of these rocks and in the valleys of mountainous districts. He will not hesitate to 
trace the origin of these soils to the degradation and decomposition of the solid rocks in their imme- 
diate neighbourhood, especially to those which occupy the surrounding eminences. But rocks differ 
much in composition. A sandstone, it is evident, in the course of time will produce a soil totally 
different in appearance and character froni that formed by the disintegration of an oolitic or slate 
rock. The first will produce a light, porous sandy or gravelly soil ; a slate rook, on the contrary, a 
stiff, more or less cold, impervious soil. From the crumbling of a limestone a calcareous soil is 
formed ; from a trap, a good, rich, fertile, generally reddish loam. Basalt rocks, which are found over 
a great part of Scotland, and here and thei-e in England, — for instance, in some few places in Cornwall, 
Gloucester, Devon, Cumberland, Hereford, &c, and in abundance in the North of Ireland, — give rise to 
friable reddish, brownish, or greyish coloured, very fertile soils. In Dorsetshire, Wiltshire, Berk- 
shire, a portion of Norfolk and Suffolk, many soils resting on the chalk formation are made up of 
decomposed chalk, with or without flints, and partake generally of a dry, loose, friable character. 
Thus a geological map of Britain, in which the districts which are covered by rocks of different kinds 
and ages are indicated by different shades of colour, may convey to the farmer a knowledge of the 
general nature, agricultural capabilities, and limits of the soils, which rest on, or may generally be 
inferred to be formed directly from the crumbling down of, their respective geological formations. 
The study of the rocks of a country is therefore of interest to the cultivator of the soil, as it will 
enable him to predict in a general way the character of the soil of a district in which certain rocks 
prevail. Though useful to the gardener, this study must benefit the farmer in a greater degree, 
because the gardener, particularly the flower-gardener, seldom has to deal with extensive districts, 
and because he has it more in his power to render himself independent of the natural resources, and 
operating on a small scale, may resort to additions and mixing of soils which the former seldom can 
practise. For this reason it is unnecessary to enter into a minute description of the soils which are 
formed in this country by the disintegration and decomposition of the several geological formations, 
and we proceed, therefore, to inquire how it is that the solid rock gradually crumbles down to powder, 
and gives rise to a more or less fertile soil. In some instances we can trace the changes rocks undergo 
hi the course of time, step by step, and refer them to their true causes ; in others only the ultimate 
products of decomposition are well described, and their- primary causes less clearly understood. This 
much is quite sure, that the causes which produce these mighty changes are various and often compli- 
cated. Some of them may be referred to chemical forces and agencies — we will call them " chemical 
causes ;" others, which are based on purely mechanical principles, we shall distinguish as " mechanical 
