SOILS — FEKTILIZERS. 517 



that the temperature of the soil is constantly and generally higher than that 

 of the air during the growing period, and thus warms the lower layers of the 

 air in which the plants grow, is considered to be of greater Importance than is 

 generally recognized. This heating of the lower layers of the air by the soil 

 amounted to from 0.1 to 5° C. in the shade to 8° in the smi. During the 

 winter, however, the conditions were reversed. In summer the temperature of 

 the surface soil subjected to sunlight was from 12 to 19° higher than that of 

 the air. At a depth of 0.1 meter this difference did not exceed from 3 to 5°. 

 As a mean of 65 observations of the temperature of the soil at a depth of 0.03 

 meter, the southern exiK)sures showed a temperature of 12.4° and the northern 

 exposures 7.9°. The difference in winter was very small, rarely exceeding 2°. 

 In summer it may be as much as 20°. Variations in soil temperature were some- 

 what smaller on a northern exix)sure than on a southern exiiosure. As between 

 southwestern and northeastei'n exposures there was very little difference. At 

 2 stations near together, one in the shade and the other in the sun, the 

 difference in temperature was 12.4° in June and 6° in March. At a depth of 0.1 

 meter the differences were insignificant. In bare soil the temperature was from 

 2 to 7° higher than in soil covered with trees or other vegetation. A certain 

 increase of temi^erature ascribed to the physiological activity of plants was 

 observed. In one case in which the general air temperature was 18.1°, temi>era- 

 tures of 18.2° over grass land at a height of from 2 to 3 cm., and 23.7° in air 

 surrounding cultivated plants in the flowering stage were observed. In some 

 cases the wind reversed the differences in temperature resulting from the nature 

 of the soil, the plant cover, and exposiire as a result of its effect on evaporation. 



Among the more general conclusions, therefore, of these investigations is that 

 each six>t of soil area has a distinct and independent set of conditions and 

 activities, which are determined primarily by the physical properties, especially 

 the structure of the soil. In other words, the moisture and temperature condi- 

 tions and to a large extent the plant growth of a given area are, especially in 

 case of wild soils, a function of the soil structure, although, as already indicated, 

 the wind may become an important factor in reversing conditions brought about 

 by the soil structure. 



An appendix to the reiwrt gives a blooming calendar, detailed observations 

 on humidity of the air and wind movement, and a short bibliography of the 

 subject. 



The data of geochemistry, F. W. Clarke (U. 8. Geol. Survey Bui. 491, 

 pp. 782). — This is a revised and enlarged second edition of a bulletin which 

 appeared first in 1908 (E. S. R., 20, p. 609). It is described as "a manual of 

 geologic chemistry, including chapters on the nature, distribution, and relative 

 abundance of the chemical elements, the composition of the atmosphere and of 

 volcanic gases and sublimates, the mineral content of surface and underground 

 waters, the nature of saline residues, the molten magma of the earth's interior, 

 the rock-forming minerals, the composition of igneous, sedimentary, and meta- 

 morphic rocks, rock metamorphism and decomposition, metallic ores, natural 

 hydrocarbons, coal, lignite, and peat." Numerous references are given to the 

 literature from which the data are drawn. 



Soils of the Eastern United States and their use, XXVI-XXVIII, J. A. 

 BoNSTEEL {U. S. Dept. Agr., Bur. Soils Circs. 49, pp. 11; 50, pp. 14; 51, pp. 11). — 

 These circulars deal respectively with the following soil types, as surveyed and 

 mapped by the Bureau of Soils: 



Circular Ifi. — The Houston clay, of which a total of 763,688 acres in 21 areas 

 in 4 States has been surveyed and mapped by the Bureau of Soils. 



" The surface soil to a variable depth is a brown or black granular clay loam 

 or clay. This is underlain by a lighter brown or yellow plastic clay snbsoil 



