PART III.—Methods of improving the soil by mechanical and by chemical means—Manures, their nature, composition, and mode of action—theory of their application in different localities. PART IV.—The results of vegetation—the nature, constitution, and nutritive properties of different kinds of produce, and by different modes of cultivation—the feeding of cattle, the making of cheese, &c. &c. The constitution and differences of various kinds of wood, and the circumstances which favour their growth. CRITICAL NOTICES. “A valuable and interesting course of lectures.”—_Quarterly Review._ “But it is unnecessary to make large extracts from a book which we hope and trust will soon be in the hands of nearly all our readers. Considering it as unquestionably the most important contribution that has recently been made to popular science, and as destined to exert an extensively beneficial influence in this country, we shall not fail to notice the forthcoming portions as soon as they appear from the press.”—_Silliman’s American Journal of Science. Notice of Part I of the American reprint._ “We think it no compliment to Professor Johnston to say, that among our own writers of the present day who have recently been endeavouring to improve our agriculture by the aid of science, there is probably no other who has been more eminently successful, or whose efforts have been more highly appreciated.”—_County Herald._ “Prof. Johnston is one who has himself done so much already for English agriculture, that to behold him still in hot pursuit of the inquiry into what _can_ be done, supplies of itself a stimulus to further exertion on the part of others.”—_Berwick Warder._ ELEMENTS OF AGRICULTURAL CHEMISTRY AND GEOLOGY. BY JAS. F. W. JOHNSTON, M.A., F.R.S., HONORARY MEMBER OF THE ROYAL ENGLISH AGRICULTURAL SOCIETY, AND AUTHOR OF “LECTURES ON AGRICULTURAL CHEMISTRY AND GEOLOGY.” NEW-YORK: WILEY AND PUTNAM. MDCCCXLII. J. P. WRIGHT, Printer, 18 New Street, N. Y. INTRODUCTION.