AN ESSAY 



ON 



CALCAREOUS MANURES. 



CHAPTER I. INTRODUCTORY. 



GENERAL DESCRIPTION OP AGRICULTURAL EARTHS AND SOILS. 

 PHYSICAL AND CHEMICAL CONSTITUENTS OF SOILS. 



IN discussions or instructions upon the fertilization of land, it 

 is an important requisite that we should correctly distinguish be- 

 tween earths and soils, and the many varieties of the latter com- 

 pound bodies. Yet the terms used for this purpose, are generally 

 misapplied ; and even among writers of high reputation and autho- 

 rity, no two agree in their definitions of soils, or modes of classifi- 

 cation. That such differences of definition, and contradiction of 

 terms, should exist, will appear the less strange, and the resulting 

 errors the more excusable, to those readers who have most care- 

 fully studied this branch of agricultural science, and who, therefore, 

 can best appreciate the difficulties of the required classification. 

 Each writer on soils is compelled to use terms in senses different 

 from the greater number of his many predecessors ; because but 

 few of them have concurred in even the most important definitions. 

 Where such great differences exist, and where no one known plan 

 of nomenclature is so free from material imperfections as to bo 

 referred to as a standard of authority, it becomes necessary for 

 every one who treats on soils to define for himself , though perhaps 

 he may thereby add still more to the general mass of confusion 

 previously existing. This necessity must serve to excuse the writer 

 for whatever is new, unauthorized, or confessedly defective in the 

 definitions and terms which will be here adopted, and used as 

 required hereafter through this treatise. It would be inferred by 

 most readers, from the general heading alone, that this introductory 

 chapter must consist mainly of definitions and explanations already 

 established by scientific authority, and generally received by and 

 known to well-informed agriculturists. This inference would be 

 correct to a considerable extent : nevertheless, there will be many 

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