[96 ECONOMIC GEOLOGY 
that soil investigation is the most fundamental of all forms 
of agricultural research.” The interpretation of chemical 
analyses requires allowance for climate, economic position, 
and biological factors. 
Climate may be especially important. If, e.g. the rainfall 
belts trend N. and S. and the rocks E. and W. the variations 
in rainfall may be the most influential factor (cf. Alway and 
Rost, Soil Science, i, 1915, p. 406). 
The most extensive soil surveys have been made in the 
United States, where by the end of 1912 they covered 
over 520,000 square miles, or 330,000,000 acres (** Soils 
of the United States,” U.S. Bur. Agric., 1913). The soils 
are classified primarily according to texture, into clay, sand, 
sandy loam, and loam, and divided inte over 1700 soil types 
based largely on climatic factors. The objects of a soil survey 
are to show the agricultural resources of a district, to pro- 
vide a basis for the scientific investigation of soil, to lead 
to its improvement and most suitable employment, and to 
enable local agricultural advisers to give cultivators reliable 
advice. Mosier and Gustafson (Soil Physics and Management 
1917, pp. 117-18) conclude, ** If the work cease with the map- 
ping of the soils, very little of real value is accomplished, as 
the soil survey is only preliminary to a more complete in- 
vestigation. If, however, the soils are analysed, field ex- 
periments carried on, reports published giving the results 
of the work, and recommendations for improved manage- 
ment made, the farmer may avail himself of all this infor- 
mation for improving his soil and his farm management 
generally.” 
Soil survey of transported soils has been undervalued owing 
to their irregularity. But sedentary soils have as sudden 
variations. Rocks composed of thin bands or lenticles of 
clay and sandstone give equally patchy soils. Some drift areas 
have a remarkably uniform soil over hundreds of square 
miles. Whether the soils are too irregular for a survey to 
be useful has to be decided independently in each case. The 
soil mapping of drift areas should not be debarred by a general 
rule.