CHEMISTRY OF HOETICULTURE. — NATIVE OE SPECIAL EARTHS. 357 
which it can be kneaded into a smooth, homogeneous mass, which retains the shape 
given to it." — Stepliens. 
The leading characters of all soils are derived from only two earths, clay and sand, the 
greater or less admixture of which stamps their peculiar character ; for the properties 
of these earths are also found to exist in purely calcareous, and purely vegetable 
soils." — Idem. 
(h) A clay loam combines, we may say, from 15 to 20 per cent, of siliceous sand with 
as much alumina in it ; but these calculations are to be received with caution, because the 
free-worldng or clodding of the loam, depends much upon the state and texture of the sand. 
It is no uncommon circumstance, that where the sand consists of a gritty gravel, a very 
large proportion of it shall be found in a state that can be separated by washing with 
water, and yet will permit the land to bind and clod after being wet ; insomuch, that it 
cannot again be worked till penetrated by more rain. Such an earth, with perhaps 60 
per cent or more of sharp, abounds in part of Berkshire, and demands the nicest 
attention on the part of the farmer. Coal-ashes, which contain much dry alumina and 
silex, afford the most effectual remedy in such cases. 
(c) If the silica be in a fine silky state, from 40 to 60 per cent, of it will constitute a 
free working, and yet unctuous loam. 
[d) Marls combine a considerable per centage of chalk ; thus, if a loam contain in 
100 parts — 
Water of Combination ... 9 parts 
Carbonate of Lime . . . . 14 to 20 „ 
Siliceous Sand . . . . 37 to 40 „ separable by water 
^1 r, o■^ on ^ A(\ \ tlie latter in a state of chemical 
CJay, with nne Silex . . . o7 to 40 „ -I • -.i i • 
' ( union with the alumina 
a genuine marly loam will be the result. I say nothing now of organic or any putrescent 
matters which always are present in fertile loams, and must form the subject of future 
investigation. At present our inquiry refers only to the basal, insoluble elements of the 
land : and such indeed, are also chalk, and oxide of iron. Of the former, enough has 
been written in a former article, combined with the above remarks on Marl [d). Oxide of 
iron, if as a perfect- — or a per-oxide — (1 equivalent of the metal with li of oxygen) is 
innocuous and insoluble, and always present in the rich brown earths. 
Having thus taken a general, though cursory glance at the bases of all good land ; 
setting aside, for the sake of argument only, the other elements, saline, vegetable, and 
animal, which are susceptible of dissolution and organic mutations, the grand question 
now presents itself, — what office do those principal basal earths perform ? And again, 
do they — can they — nourish a plant ? or, do they merely afford a matrix — a bed wherein 
the roots may fix themselves, find support, and wander in all appropriate directions in 
search of food ? These questions involve considerations of deep interest, for, aUhough it is 
impossible to suppose that any land, however poor it may be, is entirely void of any 
particle of decomposable fibrous or saline matter, yet we have authority to believe that 
trees — mere seedlings, have been planted in pots of not large dimensions, filled with the 
simplest maiden earth, and watered only with the purest water, which have grown to an 
amazing size, and to all appearance without abstracting anything from the earth, to the 
extent of -r^^th part of the wood produced. The earth, in one instance, was accurately 
weighed, the surface of it covered with lead, perforated so as just to allow the equal 
distribution of the water ; and yet, at the expiration of several years, the tree had gained 
enormously, while the loss of weight in the soil, amounted to a mere fraction. Are we 
then to conclude that trees acquire all their growth from the air, through the channels, or 
oscular pores of their leaves? Experience in culture repudiates the assumption; yet 
facts in favour of it are rather cogent. I will resume this subject — connected with 
manure — hereafter ; but in closing this article I may notice the case of two plants of 
Arbor Vitse in a neighbour's balcony, 4 or 5 feet high, which appear to me to have 
remained there winter and summer, without any change of circumstances : they are full of 
foliage and so they were in 1847, and I think long before that period. These shrubs stand 
