prise most of the argillaceous soils, and a few of 
the stiffest loams. Black soils are often churlish 
and generally deaf; brown soils are often kindly 
and generally sharp and grateful; and red soils 
are always rich. The yellowish grey, the dull 
red, and the dull brown are very little or not at 
all altered in tint by cultivation; but the bluish, 
the yellow, and the bright red become darker 
and duller by ploughing and manuring. 
The relative chemical characters of soils, both 
with reference to atmospherical connexions and 
with reference to intrinsic action, are very 
powerfully and variously modified by the cir- 
cumstances of drainage. See the article Dratn- 
1nG.—The circulation of air through soils, toge- 
ther with free play to the important action of 
oxygen, is mightily controlled by natural poro- 
sity, and by all those operations of georgy and 
culture, by which porosity is artificially increased 
or maintained. See the article AnRation.—The 
absorption of carbonic acid, ammonia, phosphu- 
retted hydrogen, sulphuretted hydrogen, and 
other importantly nutritional gases which either 
float in the atmosphere or ascend toward it from 
the decomposition of organic remains and of 
putrescent manures, is effected far more by some 
soils than by others,—and most of all by such as 
possess a maximum of carbonaceous matter in a 
state akin to that of charcoal. See the article 
AxBsoRPTION IN CHEMISTRY.—The various absorp- 
tion of heat by different soils has already been 
adverted to in connexion with the colour-cha- 
| racters; and may here be further noticed in the 
words of Sir Humphrey Davy, “ Some soils are 
much more heated by the rays of the sun, all 
other circumstances being equal, than others, 
and soils brought to the same degree of heat 
cool in different times, that is, some cool much 
faster than others. This property has been very 
little attended to in a philosophical point of 
view ; yet it is of the highest importance in agri- 
culture. In general, soils that consist princi- 
pally of a stiff white clay are difficultly heated ; 
and being usually very moist, they retain their 
heat only for a short time. Chalks are similar 
in one respect, that they are difficultly heated ; 
but being drier they retain their heat longer, 
less*being consumed in causing the evaporation 
of their moisture. A black soil, containing much 
soft vegetable matter, is most heated by the sun 
and air; and the coloured soils, and the soils 
containing much carbonaceous matter, or ferru- 
ginous matter, exposed under equal circum- 
stances to the sun, acquire a much higher tem- 
perature than pale-coloured soils. When soils are 
perfectly dry, those that most readily become 
heated by the solar rays likewise cool most ra- 
| pidly; but I have ascertained by experiment, 
that the darkest coloured dry soil, (that which 
contains abundance of animal or vegetable mat- 
_ ter, substances which most facilitate the diminu- 
259 
of the effect of solar heat, will cool more slowly 
than a wet pale soil, entirely composed of earthy 
matter.” — The retention of the decomposing 
substance or of the recombined principles of or- 
ganic remains, especially as artificiaily supplied 
in the form of manure, is much greater and more 
economizing by argillaceous and loamy and cal- 
careous soils than by silicious ones, or by sandy 
soils containing a considerable intermixture of 
lime or chalk than by mere sands and gravels. 
—Close soils and open ones are very differently 
affected by frost and thaw. All clays and stiff 
loams, in consequence of the great expansion 
which results from the freezing of the water in 
their interstices, are more dissevered and disin- 
tegrated by frost than by the most elaborate till- 
age ; and when thaw comes, they are left open 
and porous, freely exposed to the circulation of 
air and moisture, which decomposes their alka- 
line constituents, elaborates their stores of inor- 
ganic nutriment for plants, and renders their 
whole mass almost as powdery and “ mellow” as 
that of naturally open soils. But sands, loamy 
sands, many calcareous and humous soils, and 
even some sandy loams, when frozen soon after 
rain, or otherwise in a wet state, are so greatly 
expanded as to be icy and resonant ; and, when 
thawed, they retain their increased bulk, and 
have a largely cellular or honeycombed texture, 
and suffer erosion and winnowing by the exces- 
sive permeation of air, and allow their young 
plants, particularly wheat and red clover, to be 
loosened from their root-hold, “thrown out,” 
and either ruptured or starved to death.—The 
absorbing of moisture from the air in dry condi- 
tions of the ground, so as by its imbibitions dur- 
ing the night to counteract the effect of evapo- | 
ration during the day, is a function eminently 
connected with fertility, and is performed in 
widely different degrees by different soils. Very 
powdery or finely pulverized soils of any one 
kind absorb much more moisture than coarsely 
granular or badly tilled ones of the same kind ; 
and humous substances in any soil absorb more 
moisture than fine carbonate of magnesia,—fine 
carbonate of magnesia more than garden mould or 
grey pure clay,—garden mould or grey pure clay 
more than loamy clay or slaty marl or sandy clay, 
—and any of these three very greatly more than 
gypsum powder, calcareous sand, or silicious sand. 
The stiff clays approaching in nature to pipe 
clays, which imbibe the greatest quantity of water 
when it is poured upon them in a liquid form, 
do not by any means absorb the greatest quan- 
tity of moisture from the atmosphere in dry 
weather, but consolidate and contract and pre- 
sent a diminished and close surface to the air, 
and become arid and exsiccated, and eventually 
allow their vegetation to be almost as severely 
burnt up as on sands. Soils, on the other hand, 
which are not remarkable for imbibing large 
tion of temperature,) when heated to the same | doses of water in its liquid state, but which have 
degree, provided it be within the common limits | an open texture and a finely divided condition, 
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