2 BULLETIN" 122, TJ. S. DEPARTMENT OF AGRICULTURE. 



[ 



based primarily on texture and other obvious physical properties. 

 These qualities serve to divide soils into types which are further 

 grouped into series and provinces. The provinces east of the Missis- 

 sippi are as follows: Piedmont Plateau, Appalachian Mountain and 

 Plateau, Limestone Valley and Uplands, Glacial and Loessial, Atlantic 

 and Gulf Coastal Plains, and River Flood Plains. 1 



In the selection of samples for analysis only important agricultural 

 types were chosen. They were selected to represent various textures, 

 provinces, and conditions of fertility. A comparatively small number 

 of soils were examined. Owing to the time-consuming character 

 of the analysis and the inability to secure samples from places where 

 field parties were not working, the samples do not represent as wide 

 a range as desired. 



DISTRIBUTION OF THE RARER ELEMENTS. 



It would seem that all elements present in the rocks from which a 

 soil is formed would be present in the soil, for the soil has been shown 

 to contain all the more common rock-forming minerals. 2 While 

 there is great change in chemical composition as a rock weathers to a 

 soil, and much of the more soluble constituents are washed away, it 

 is hardly conceivable that any one element should completely dis- 

 appear. Had the mineral which contained this one element com- 

 pletely disintegrated, the weathered products might contain the ele- 

 ment in an insoluble form, other elements might combine with it to 

 form an insoluble compound, or in case none of these things hap- 

 pened, the soil possesses such a marked capacity for physical absorp- 

 tion that it is doubtful if it would yield the last traces of the soluble 

 element to the soil solution. Further, the soil is by no means sta- 

 tionary, but is continually being translocated by wind and water. 8 

 It is evident that such processes add to the chemical complexity of 

 the soil. 



Provided methods of analysis were sufficiently delicate, we would 

 expect to find in the soil every element for which it is examined, and it 

 would seem, judging from the extreme complexity of the soil, that fail- 

 ure to find an element in the soil shows the method of analysis of 

 insufficient delicacy rather than the absence of the element. 



The distribution of the elements in igneous rocks is given by Wash- 

 ington,* special attention being paid to the elements in smaller 

 amounts. From this work and from that of Clarke 8 and Hillebrand, 8 



1 Bui. 96, Bureau of Soils, CJ. S. Dept. Agriculture (1913), upon which descriptions of the types are based. 



a See F. K. Cameron and J. M. Bell, Bui. 30, Bureau of Soils, U. S. Dept. Agriculture (1905). 



Tor a full discussion see E. E. Free, Bui. No. 68, Bureau of Soils, U. S. Dept. Agriculture. 



« Trans. Am. Inst. Min. Eng., 39, 735 (190S). 



'Data of Geochemistry, Bui. 491, U. S. Geol. Survey (1911). 



6 Analysis of Silicate and Carbonate Rocks, Bui. 422, U. S. Geol. Survey (1910). 



