Development of Soil Survey 71 



tions which are the mature expression of various sets of climatic con- 

 ditions. Mature soils develop vi^here topography favors drainage and 

 aeration and the accumulation of v^^eathered products. On rolling or 

 eroded lands the soil section may be immature, and on flat lands it may 

 have passed through maturity to old age, marked by strongly leached 

 surface and so-called "hardpan" layers. In associated lands with a 

 high water table there is preservation, rather than weathering, of the 

 parent materials, and accumulation of organic remains. Weathering 

 of alternately wet and dry lands proceeds in a complex manner. 



The chief factors of climate affecting soils are conditions of heat 

 and moisture. In this country east of the Rocky Mountains there are 

 two or three temperature zones and three or four zones according to 

 rainfall and humidity, and as the resultant of prevailing climate Marbut 

 has described ten distinct soil families. These families may be grouped 

 into two soil orders — the arid and the humid. The soils of the arid order 

 are marked by a zone of carbonate accumulation in the soil section, while 

 those of the humid order lack this zone, but are leached and often acid. 



At present a soil survey embraces several phases. First is the strictly 

 research work designed to collect enough data to serve as a basis of a 

 natural and sound classification, and provide adequate nomenclature so 

 that all soil science may be related to soil types. A part of the records 

 of soil survey is in the form of maps, and this map making is one of 

 the chief functions of the field workers. A soil survey includes some 

 physical and chemical tests in both field and laboratory. Since the 

 work is supported chiefly by agricultural appropriations it is expected 

 to justify its existence by ultimate benefits to the farming interests. 

 Efforts to be of more immediate benefit take the form of aiding the in- 

 terpretation of results on experimental fields and of showing where these 

 results apply, or of furnishing data to extension workers. However, 

 most soil survey workers feel that an attempt to occupy middle ground 

 between the "practical and scientific" promises little progress in either 

 direction, and believe that sound soil science is a prerequisite to sound 

 advice on practical soil problems. It is hoped to collect and organize 

 soil facts into a science comparable with other branches of knowledge. 

 Just as we receive aid from geologists, botanists, bacteriologists, etc., 

 they should be benefited by a fund of exact knowledge whenever the 

 soil is involved in their problems. 



In Indiana the soil survey has passed through several stages. The 

 U. S. Bureau of Soils mapped ten counties between 1901 and 1908. Be- 

 ginning about 1907 the State Geological Department carried on work 

 under the name of "Soil Survey" which eventually covered most of 

 southern Indiana. In this the classifications were based more on geolog- 

 ical formations than on soil, and the mapping was very general. In 

 1912 the Bureau of Soils resumed work in the state, now in co-operation 

 with the State Geologist. Under this arrangement sixteen counties were 

 mapped in the central and northern part of the state. It includes some 

 very good work needing little revision to bring it up to date. Nothing 

 was done in 1918. 



In 1919 the U. S. Bureau of Soils began co-operation with the 

 Soils and Crops Department of the Purdue University Agricultural 



