Continued from page 182.) Manures.The subject of manures is treated somewhat extensively, and as it is one of great importance to our farmers, and as we have a great many subscribers amongst our agriculturists, we will continue this subject from week to week, until it is completed, in order to have the subject finished about the period when spring cultivation opens. Every substance which has been used to improve the natural soil, or to restore to it the fertility which is diminished by the crops annually carried away, has been included in the name of manure. Ib is well known to all practical agriculturists that the texture of the soil, and the proportions ot the earths of which it is composed, are the first and most important conditions of its productive powers. Where there is a good natural loam, which retains moisture without being overcharged with wet, and permits the influence of the atmosphere to pervade H, the crops cannot fail to be more certain and remunerating than in loose sand, or tenacious clays ; but ot the same time it is equally true, that the best texture of soil will not produce good crops tor any length of time without the help of manure, to recruit the loss produced by vegetation. The methods employed in the cultivation of land are different in every country ; and when we inquire the cause ot these differences, we receive the answer that they depend upon circumstances. No answer could show ignorance more plainly, since few have ever yet devoted themselves to ascertain what these circumstances are. Thus, also, when we inquire in what manner manure acts, we are answered that the excrements of men and animals are supposed to contain an incomprehensible something which assists in the nutrition of plants, and increases their size. This opinion is otten embraced without even an attempt being made to discover the component parts of manure, or to become acquainted with its nature. In addition to the general conditions, such as heat, light, moisture, and the component parts of thermosphere, which are 'necessary for the growth of all plants, certain substances are found to exercise a peculiar influence on the development of particular plants. These substances either are already contained in the soil, or are supplied to it in the form of substances known under the general name of manure. But what does the soil contain, and what are the components of the substances used as a manure 1 Until these points are de-termined, a rational system of agriculture cannot exist. The power and knowledge of the physiologist. agriculturist, and chemist must be united for the complete solution of these questions. The general object of agriculture is to produce, in the mOit advantageous manner, cer-tain qualities, or a maximum size, in certain parts or organs 01 particular plants. Now this object can be attained only by the application of those parts or organs, or by supply-ing the conditions necessary to the produc-tion of the qualities desired_ The rules of a rational system of agricul-ture should enable us, therefore, to give to each plant that which it requires for the attainment of the object in view. As the composition of soils forms an important feature in the profession of agriculture, it will be our duty to explain, as briefly as possible, some of those which have the most distinct characters from their connections with different geological formations. There are various modes of distinguishing soils without entering into a minute analysis of their component parts. The simplest and most natural is, to compare their texture, the size and form of the visible particles of which they are composed, and to trace the probable source of their original formation trom the minerals which are found around or below them. The science of geology is of great utility in aiding us to compare different soils and ascertain their composition. The soils which are immediately derived "rom those rocks, in which no traces of organic remains are to be found, consist either of visible fragments of hard minerals, which are not affectad by exposure to air or water; or of minuter particles of the same, of which the shape is not readily distinguished by the naked eye. When they are altogether composed of visible particles and stones, the water readily passes through them ; and unless they are kept continually moist by a regular irrigation, without any stagnation of the water, they are absolutely incapable of sustaining vegetation. It is seldom, however, that any gravel or sand does not contain any portion of earth or other matter, of which the particles become invisible when diffused through water, and to which we will here give the name of impalpable substance. A certain portion of this finer part ot the soil: and its due admixture with the coarser, especially where there is some regular gradation of size, and no stones ot too large dimensions to obstruct the instruments of tillage, may be considered as essential to fertility. The soils which have been formed from the disintegration and decomposition of the primitive rocks, such as granite, basalt, or limestone, and those which contain all these minerals minutely divided and intimately mixed, are always naturally fertile a::d soon enriched by cultivation. The hard particles oj quartz maintain a certain porosity in the soil, which allows air and moisture to circulate, while the alumina prevents its too rapid evaporation. The silicate of potash is highly favorable to the vegetation of those plant. which contain silica in their stems ; in fact silica is present in the ashes of nearly all plants, having entered the plants by means of alkalies. The primitive limestone, which is very hard, is yet gradually decomposed by the action 01 air and water, being in a very small degree soluble in the latter. The water which flows through these rocks is soon saturated ; but when it springs out and comes to the light, the carbonate of lime is deposited by the evaporation of the water, and if this meets with the clay which results lrom the decomposition of the slate, it forms a marl, which, naturally or artificially added to sili cious sand, forms the basis of a very good soil, particularly well adapted to pasture. The soils, which have evidently been formed from the rocks, which are supposed to be of secondary formation, are fertile according to the proportion ot the earths of these rocks, which they contain. It is of these chiefly that those loose, sandy soils are formed, of which the particles appear as distinct crystals, easily distinguishable with the aid 01 a lens, or even by a naked eye. Air and water have been the chief agents in the decompositions of those secondary rocks called sandstones, and agitation in water has washed from them the finer portions which have remained suspended. The immense sandy plains which are for the most part barren, have probably once been the shores of the sea, from which the waves have washed all that portion which was impalpable and easily suspended in water, depositing this in the depths, which, by some convulsion in nature, may some time or other be raised above the level of the waters, and form hills or plains of clay. Argillaceous earth exists, in some proportion, in almost every rock. Some of the hardest gems are chiefly composed of alumina. It has the property, when mixed with other substances, as silica or lime, of fusing into a stone of great hardness and insolubility. In this state, its effect on the soil is not to be distinguished from that of silica ; and by burning common clay, or clay mixed with carbonate of lime, a sandy substance is produced, resembling burnt brick, which tends greatly to improve the texture of those clays which contain little or no sand in their composition. It must be remembered that the stiff est clays contain little or no sand in their composition_ It must be remembered that the stiff est clays contain a large portion of si-ica in an impalpable state; but this, instead of correcting their impermeable and plastic nature, rather adds to it. It is only palpable sand, which, with clay, forms what is commonly called loam, and which, when the sand is in due proportion with a mixture. of organic matter, forms the richest and most easily cultivated soils. Some of the rocks of secondary formation contain a considerable portion of alumina and lime ; and when these earths meet with crystallized sand, a compound, or rather a mixture, is formed, which has all the requisite qualities, as to texture, to produce the most lertile loams. The only deficiency is organic matter; but this is so readily accumulated wherever vegetation is established, or can be 80 easily added artificially, that these loams may be always looked upon as the most favorable soils for agricultural operations, and if a considerable depth of loam is found, which neither retains water too long nor aliows it to percolate too rapidly, it may be looked upon as a soil eminently capable 01 the highest degree of cultivation. It is known that the aluminous minerals are the most widely diffused on the surface of the earth ; and all fertile soils, or soils capable of culture, contain alumina as an invaluable con-stituent. There must, therefore be something in aluminous earth which enables It to exercise an influence on the life of plants, and to assist in their development. The property on which this depends is that of its invariably containing potash alld soda
This article was originally published with the title "Riddle's Report of the Great Exhibition"