THE SOIL SURVEY 733 



collected on one or more squares of oilcloth, or it may be 

 placed directly in the appropriate bags. The worm of the 

 auger having been cleaned, it is inserted into the same 

 hole and advanced until it is again full, when it is with- 

 drawn and cleaned as before. This operation is repeated 

 until the desired depth is reached. Where the soil is a 

 very heavy clay,, it may be advisable to only partially 

 fill the worm with soil. Where the soil is very dry and 

 pulverizes to a dust, it may slip off the worm, in which 

 case water may be added to make it adhere. The upper 

 part of the hole should be cleaned, and it may be slightly 

 enlarged so as to prevent contamination with the material 

 from the lower part of the section. Where there is rubbish 

 on the surface, this should be removed previous to begin- 

 ning the collection of the sample. 



In very stony soil the auger is not suited to taking a 

 sample, either for examination or for record. In such 

 soil a shovel may be used, or the sample may be taken in 

 a road or some other cut by means of a geologist's hammer. 



The face of the section should be removed to a depth 

 of several inches, in order to eliminate weathered or con- 

 taminated material which may not be typical of the soil 

 section. Usually a difference in color and physical 

 properties of the soil indicates a modification of the typi- 

 cal material. 



629. The accuracy and detail of the soil survey. The 

 accuracy and detail of the soil survey depend on many 

 things. Assuming an adequate preparation on the part 

 of the field man, there are limitations in accuracy imposed 

 by the scale on which the map is made and the nature of 

 the soil. The smaller the scale of the map used in the 

 field, the less is the detail that may be represented. The 

 commonest scale employed is one inch to a mile. Some 



