x.] MAPPING SOILS 335 



further subdivisions due to the causes enumerated 

 above, or to the local movements of rain-wash or ill- 

 defined drift, that may alter the character of the soil 

 without being of any particular geological importance. 



A soil map will consist of a " drift " map, with some 

 further details showing the superficial formations occupy- 

 ing the surface of the ground, and notes regarding the 

 local variations in the type of soil derived from each 

 particular stratum. The aim of a soil survey is to 

 carry further the work of the geological survey as 

 regards the superficial formations ; the only classifica- 

 tion which can be adapted will be one based upon the 

 physical texture of the soil, and indicated by such 

 conventional terms as clays, clay loams, sandy loams, 

 marls, etc. At the same time, the map must indicate 

 the various origin of the different loams which may 

 be found in the area under survey, and, by reference 

 to the accompanying text, should give those details 

 of physical structure and chemical constitution which 

 characterise the soil, but which cannot be set out 

 except by an over-elaborate classification. 



The field portion of the work of a soil survey con- 

 sists in the exploration of the subsoil by means of 

 an auger, aided by any natural sections which may 

 be displayed. The boundary between two soil types 

 may generally thus be laid down by the aspect of the 

 soil and subsoil ; from time to time, however, samples 

 must be retained for more detailed examination in 

 the laboratory, whenever the look and touch of the 

 material are not sufficient for a decision in situ. An 

 immediate examination with the microscope, the 

 behaviour of the soil with acid, or a rough sifting in 

 a stream of water, will, as a rule, be sufficient to 

 refer a given example of subsoil to one type or another. 

 Complicated cases arise from time to time, especially in 



