SUB-PROVINCES, CLASSES, TYPES AND SURVEYS 117 



than a single farm. The study of a sample that is ordinarily sent 

 in by a farmer for analysis means little to the agriculture of a 

 state or even a county. The samples must be taken from areas that 

 represent some distinct type of soil and care must be taken to avoid 

 errors due to local variations. In order to place the sampling and 

 analysis of soils upon a truly scientific basis, a soil survey in which 

 the different types of soil are located on a map should be made, 

 and the samples secured according to the types shown by the soil 

 map. 



Soils are sufficiently uniform and constant in texture to be 

 divided into distinct types with fairly well defined boundaries, and 

 a soil survey consists in working out these boundaries in the field 

 and locating them on a map. The type is the unit of the soil sur- 

 vey. The soils are examined to a depth of 40 inches by means of 

 an auger, and the variations not only of the surface but also of sub- 

 surface and subsoil are noted. In some cases where the deeper sub- 

 soil is peculiar and affects drainage, the examination may extend 

 to a depth of 80 inches. This applies especially where sand or 

 gravel subsoils occur. 



Surveys in Different States. Some soil survey work has been 

 carried on in every state. It was begun in 1899 and since then 

 479,059,000 acres, or 25.2 per cent of area of the United States, have 

 been surveyed. The soil survey of one state, Rhode Island, has 

 been completed. Xearly all of the work that has been done has been 

 in cooperation with the Bureau of Soils, this organization furnishing 

 half the men and their expenses, while the state does an equal 

 amount. In a few cases, as in Kentucky and Illinois, survey work 

 has been done independently of the Bureau of Soils. In the latter 

 state, GO per cent of the entire area has been surveyed. 



1. Objects of a Soil Survey. The objects of a soil survey may 

 be stated as follows: (a) to take an invoice of the agricultural 

 resources of a country, for they depend first of all upon the soils; 

 (b) to provide a scientific basis for consistent soil investigation so 

 that time may be used to the best advantage in studying the various 

 types and problems; (c) to furnish a basis for intelligent recom- 

 mendations for permanent soil improvement; (d) to give the farmer 

 who desires to study and improve his soil the information necessary ; 

 (e) in many counties to give to the county agriculturist a valuable 

 asset to aid in his work ; and (f ) to give a basis for the introduction 

 of new crops or farm practices. If the work ceases with the mapping 



