The scientific principles upon which the art of culture depends, have not hitherto been sufficiently understood or appreciated by practical men. Into the causes of this I shall not here inquire. I may remark, however, that if Agriculture is ever to be brought to that comparative state of perfection to which many other arts have already attained, it will only be by availing itself, as they have done, of the many aids which Science offers to it; and that, if the practical man is ever to realize upon his farm all the advantages which Science is capable of placing within his reach, it will only be when he has become so far acquainted with the connection that exists between the art by which he lives and the sciences, especially of Chemistry and Geology, as to be prepared to listen with candour to the suggestions they are ready to make to him, and to attach their proper value to the explanations of his various processes which they are capable of affording. The following little Treatise is intended to present a familiar outline of the subjects of _Agricultural Chemistry and Geology_, as treated of more at large in my LECTURES, of which the first Part is now before the public. What in this work has necessarily been taken for granted, or briefly noticed, is in the LECTURES examined, discussed, or more fully detailed. _Durham, 8th April, 1842._ CONTENTS. CHAPTER I. PAGE Distinction between Organic and Inorganic Substances —The Ash of Plants—Constitution of the Organic Parts of Plants—Preparation and Properties of Carbon, Oxygen, Hydrogen, and Nitrogen—Meaning of Chemical Combination. 13 CHAPTER II. Form in which these different Substances enter into Plants—Properties of the Carbonic, Humic, and Ulmic Acids; of Water, of Ammonia, and of Nitric Acid—Constitution of the Atmosphere. 25 CHAPTER III. Structure of Plants—Mode in which their Nourishment is obtained—Growth and Substance of Plants— Production of their Substance from the Food they imbibe—Mutual Transformations of Starch, Sugar, and Woody Fibre. 38 CHAPTER IV. Of the Inorganic Constituents of Plants—Their immediate Source—Their Nature—Quantity of each in certain common Crops. 49 CHAPTER V. Of Soils—Their Organic and Inorganic Portions—Saline Matter in Soils—Examination and Classification of Soils—Diversities of Soils and Subsoils. 67 CHAPTER VI.