THE SOIL SURVEY 731 



facts, particularly concerning the geology of the region, 

 should be familiar to the survey man before active field 

 work is begun. It is easier and results in a greater degree 

 of accuracy to first recognize the larger divisions of an 

 area of soil, and later work out the types, than to be con- 

 cerned from the very beginning entirely with these ele- 

 mental subdivisions. 



During the progress of the field observation the rela- 

 tionship of each type of soil to natural and cultivated 

 plants should be studied, and the tillage properties of the 

 soil noted. The farmers also may be interviewed con- 

 cerning their soils, as to tillage properties, crop relations, 

 and response to methods of improvement. In short, all 

 available data concerning the character of the soils of the 

 region should be sought. 



Records are made in the field notebook descriptive of 

 the average character of each type of soil. The descrip- 

 tion of typical borings may be recorded and their location 

 noted on the map. Preliminary samples may be taken 

 and sent to the central laboratory for physical or chemical 

 examination, to check the judgment of the field man. 



628. Collection of soil samples. — Samples of soil for 

 laboratory examination should be taken only after the 

 field man is thoroughly familiar with each type of soil 

 and can select a location that accurately represents the 

 average material of the type. Attention should be given 

 to the slope, drainage, abnormal modifications, and 

 manurial treatment of the soil at that point. Therefore, 

 in survey work samples are collected only in the latter 

 part of the season. One or more samples of each im- 

 portant type of soil are taken. The material, to the 

 amount of a quart, is preserved in cloth bags. Usually 

 each sample is divided into two parts, one representing 



