WEATHERING 43 



by glaciation, and (2) transported soil. Transported soils may be 

 further classified as (a) alluvial, those which have been carried and 

 deposited by streams, and which vary greatly in composition from the 

 finest clay to coarse gravel ; (b) glacial soils which in any place may 

 vary greatly, both in the character and the size of their constituents 

 (p. 663) ; (c) soils of sand and clay deposited by the winds, such as the 

 fertile loess of China (p. 53) and of the western part of the United 

 States, and (d) talus soils of mountain regions. 



Removal of Soil. — When, by deforestation, overgrazing by 

 animals, or other causes, the vegetation which prevented the washing 

 of the soil is removed, the soil may be carried away rapidly, and a 

 fertile region may become almost a desert. This appears to have been 

 true of portions of China and Greece. When the fertile soil is once 

 removed, it is difficult for plants ever again to gain a foothold, and the 

 region may be permanently desolated. It is stated that a single 

 lumberman may in fifty years deprive the human race of soil that 

 required tens of thousands of years to form. 



REFERENCES FOR WEATHERING 



Buckley, E. R., — Building and Ornamental Stones : Bull. Wis. Geol. and Nat. Hist. 



Surv. No. 4, 1899, pp. 11-34. 

 Dana, J. D., — Manual of Geology, pp. 1 18-129; 158-159. 

 De Martonne, E., — Geographie Physique, 1909, pp. 404-411. 

 Geikie, A., — Textbook of Geology, 4th ed., Vol. 1, pp. 447-465. 

 Haug, E., — Traite'de Geologie, 1911, pp. 371-401. 

 Merrill, G. P., — Rocks, Rock-Weathering and Soils, pp. 173-285. 

 Shaler, N. S., — Aspects of the Earth, pp. 300-339. 



