86 SOILS. 



Rock Pozvder; Sand, Silt and Dust. 



The powdery (sandy and silty) constituents of soils usually 

 constitute the greater part of their mass; and the proportions 

 present of the several grades of fineness exert a most decisive 

 influence upon their cultural qualities, and very commonly 

 upon their agricultural value also. It is needless to add that 

 the kind of mineral of which they consist or from which they 

 \vere formed, is also of great importance in determining the 

 quality of soils from the standpoint of the chemist, with respect 

 to their content of mineral plant- food. 



WEATHERING IN HUMID AND ARID REGIONS. 



Sands of the Humid Regions. As has already been stated, 

 " sand " is usually understood to be, in the main, quartz more 

 or less finely pulverized, generally intermingled with a few 

 grains of other minerals. With this understanding, since 

 quartz is practically inert with respect to plant nutrition, it 

 follows that soils consisting mainly of this substance contain 

 but little plant-food ; hence the common expression " poor, 

 sandy land," the outcome of the experience had in Europe and 

 in the Eastern United States, and which until recently has been 

 held to be of general application. The " sands of the desert " 

 have, both in ordinary life and in poetry, always stood as the 

 symbol of sterility. 



Thus the sandy lands ( " sand hammocks " ) of Florida, the (long- 

 leaf) pine lands of the Gulf States, the " pine barrens " of New Jersey 

 and of Michigan, are noted both for their sandy soils and their sterility 

 after brief cultivation ; necessitating fertilization within a. few years 

 from the time of occupation. In Europe, the " Heide " (heather) 

 soils of northeastern Germany are of the same cultural character. 



Sands of the Arid Regions. The experience of arid coun- 

 tries however, has long ago shown that some very sandy lands 

 c. g., such as form the oases of the north African deserts- 

 may be extremely productive when irrigated, and also of con- 

 siderable durability. Actual experience and close investiga- 

 tion given this subject in the arid regions of the United States 

 has fully demonstrated that lands appearing to the casual ob- 



