PRESIDENTIAL ADDRESS. — SECTION II. 37 



As the distribution of the vegetation has been noted, so the 

 distribution of the corresponding soil types is hkewise to be 

 observed. During the fifteen years that the Soil Bureau of the 

 United States Government has been at work, detailed soil maps, 

 on the scale of a mile to the inch, have been published for a total 

 area of 150,000 square miles. These maps show how the different 

 soil types are distributed over this wide area. The Bureau has 

 given so good a lead in the matter of soil classification on a physical 

 basis that I feel constrained briefly to summarise its methods. 

 The practice is to classify soils in types, series and provinces. Soils 

 identical in origin, texture, structure and colour are taken to 

 belong to one and the same type, and are given a type-name ac- 

 cordingly. By origin is meant geological origin ; all soils derived 

 from one particular geological series, or, where greater discrimina- 

 tion is possible, from one particular member of a geological series 

 would be considered as identical in origin. By texture is meant 

 the relative proportions of different sized mineral particles which 

 a soil contains. To determine these requires the process of 

 mechanical analysis, and soils are by its means divided into silts, 

 loams, clays, sands, and so on. When speaking of texture the 

 variation of texture between the surface and subsoil layers to a 

 depth of, say, three feet is implied. A layer of sand may rest upon 

 a subsoil of loam, and this would be different in type from that 

 of a soil which is sandy throughout its whole depth. In soils of a 

 common origin, therefore, it is difference of texture that ultimately 

 determines the type. All soils that are one in origin, and alike in 

 colour, but differ in texture, are grouped together into one soil 

 series. What has been called the Norfolk series of soils extends 

 over nearly ten million acres in the States of Florida, Georgia, 

 Alabama and others adjacent. Within that series there are 

 thirteen types of soil, the most extensive being the Norfolk fine 

 sandy loam, which covers over three million acres. The geo- 

 graphical name Norfolk is here used as a series name, the term 

 expressive of the texture indicating the precise type of soil. 



Differences of colour are considered sufficient ground for placing 

 in separate series soils which are identical in origin and texture, 

 since 



" this colour difference stands for a difference in the chemical changes which 

 go on in the soil, and which are necessary for the welfare of certain crops."* 



So, too, difference of structure is reason enough for constituting a 

 fresh soil series, or for at least temporarily leaving unclassified 

 soils exhibiting such peculiarities. Greater compactness, for 

 instance, or a more pronounced open structure would give cause 

 for such discrimination. Hence, while it is usual to assign to 

 one series soils of the same origin and resembling each othei" in 

 structure and colour, the texture of the soil indicates its position 

 within that series. 



As soils of various types are classified in series, so the series are 

 grouped into provinces, dependent upon mutual resemblances 



* M. Whitney: " Soils of the United States," U.S. Dept. of Aa:r. Bureau 

 of Soils, Bull. 55, p. 23. 



