70 Proceedings of Indiana Academy of Science 



world. About the same time an independent start was being made in 

 this country where the recognized pioneer is Prof. Milton Whitney, 

 Chief of the U. S. Bureau of Soils. 



Russian soil survey progressed until interrupted by the war and has 

 since been resumed. In the United States it has grown continuously, 

 largely through work of the U. S. Bureau of Soils, with or without 

 the co-operation of various state agencies. Some states have carried 

 on independent work, and naturally there has been great divergence in 

 the methods and products of the various surveys, but all have classified 

 lands upon some basis and have shown the location of the classes on a 

 map. That is the essence of soil survey. It is primarily field work 

 designed to identify, describe, classify, correlate and map soils. In 

 recent years the tendency is to enlist the aid of all branches of science 

 which have any contact with the soil and to consider correlative labora- 

 tory work, experiments and extension as integral parts of a complete 

 survey. 



What, then is the true soil? Marbut defines it as the weathered 

 surface horizon of the earth's crust, which forms a natural body, de- 

 veloped by natural forces acting through natural processes upon natural 

 materials. The soil embraces that layer of the earth's surface having 

 the most abundant and complex flora and fauna. It is the meeting 

 ground of the organic and inorganic materials. Soil is dynamic and 

 everchanging. It passes through youth, maturity, old age, rejuvenation 

 and transmigration. The one-sided observation of soils, chiefly from 

 the top, contributed to general ignorance of their nature. Cultivation 

 mutilated the true soil. Soil survey workers went a little deeper with 

 soil augers and learned something from the mixed and displaced ma- 

 terial they brought up, but made the mistake of limiting the study to 

 three feet or some other arbitrary depth. Even today this idea persists 

 in the form of analyses of the surface three feet divided into arbitrary 

 layers. Yet who would attempt to study corn by cutting three feet 

 off of the tassel end of stalks standing from two to ten feet high, then 

 subdividing these lengths into segments for analysis? 



A scientific classification of soils must be on the basis of features 

 of the soils themselves, rather than on the growth they support or the 

 way the materials accumulated. The characteristic features by which 

 a soil type or species is recognized and identified and classified are 

 embodied in the natural soil section extending from the surface to 

 the unweathered parent materials, whether it be one or twenty feet 

 below. This soil section is made up of natui'al horizontal layers which 

 are different from each other but relatively unifoim within each, as to 

 color, texture, structure, thickness and chemical composition. Each 

 soil type has a definite number of layers in the same relative arrange- 

 ment, and is derived from geologic parent materials of a certain 

 character. 



A soil series or genus includes soil types which are practically 

 alike save in the texture of the upper layers. Formerly, soil series 

 were grouped into provinces which corresponded to certain geological 

 features of the country, but a more scientific classification results from 

 grouping the series into families according to features of the soil sec- 



