n6 SCIENCE AND SOIL 



715, most of which have been grouped into 86 soil series; and the 

 following extracts from Bureau of Soils Bulletin 55 (1909), de- 

 scriptive of these soils, cannot fail to be of interest and value to 

 the student of American soils. 



CLASSIFICATION OF SOILS 



"The texture of the soil is expressed in the mechanical analysis by a separa- 

 tion into seven grades, the sizes of which are arbitrarily fixed. The results of 

 the analysis show the percentages of sand, silt, and clay. " 



"When, aside from texture, the physical and chemical properties of the 

 soil and its method of formation are alike, we have what we call a soil series, 

 extending from the coarse gravelly or sandy soils on the one side to the finer 

 silt and clay soils on the other, and in such a series the texture of the soil deter- 

 mines the distribution of crops. 



" It would be a comparatively simple matter to compare and classify soils 

 according to the mechanical analysis or texture, but this standard alone is 

 not sufficient, and the problem is in reality a very difficult thing, for in working 

 out the relation of the soils to crops, other factors enter which must be recognized 

 in the correlation. One of the most important of these is the structure or 

 the arrangement of the mineral matter. In some soils the mineral particles 

 have a granular arrangement of flocculated masses, making the soil loose and 

 porous. In others the grains appear to have no such coherency, but exist in 

 a compact form, making the soil hard and compact. We also have the gumbo 

 and adobe soils and others that are exceedingly plastic. Then, again, the 

 amount and character of the organic matter influences not only the productive 

 capacity of the soil, but its adaptation to crops, while the color of the soil has 

 to be considered as indicative of certain obsure chemical or physical relations 

 that influence the adaptation and productivity. The drainage features also 

 come in, often with material influence on the organic constituents, on the aera- 

 tion, and on oxidation processes. " 



"The experienced soil-survey man can judge very accurately of the texture of 

 the soil material, but even his judgment, before being accepted, is always 

 confirmed by mechanical analysis. 



" Where soils have a common origin and differ only in texture and are alike in 

 color and in physical properties other than those affected by texture, they are 

 arranged in what we call a series having the soil generic name with qualifying 

 textural terms. We have, for example, the Miami gravelly loam, the Miami 

 fine sand, the Miami sandy loam, the Miami silt loam, and the Miami clay 

 loam as prominent types in the Miami series. In this particular series we 

 have fourteen types, and possibly two or three other types will be encountered. 

 In the Norfolk series we have twelve types." 



"If the texture and structure of two soils is the same, and one differs in a 

 marked degree from the series color, and that departure is fairly constant and 



