88 OUTLINES OF FORESTRY. 



out by Geikie, in his " Text-Book of Geology," * 

 on page 456. 



" The protective influence of vegetation is well known. 



" 1. The formation of a stratum of turf protects soil and rocks 

 from being rapidly removed by rain or wind. Hence, the 

 surface of a district so protected is denuded with extreme 

 slowness except along the lines of its water- courses. 



" 2. Many plants, even without forming a layer of turf, serve 

 by their roots or branches to protect the loose sand or soil on 

 which they grow from being removed by wind. The common 

 sand-carex and other arenaceous plants bind littoral sand- 

 dunes and give them a permanence which would at once be 

 destroyed were the sand laid bare again to storms. In North 

 America the sandy tracts of the Western Territories are in 

 many places protected by the sage-brush and grease-wood. 

 The growth of shrubs and brushwood along the course of a 

 stream not only keeps the alluvial banks from being so easily 

 undermined and removed as would otherwise be the case, but 

 serves to arrest the sediment in floods, filtering the water and 

 thereby adding to the height of the flood-plain. On some parts 

 of the west coast of France extensive ranges of sand-hills have 

 been gradually planted with pine woods, which, while prevent- 

 ing the destructive inland march of the sand, also yield a large 

 revenue in timber, and have so influenced the climate as to 

 make these districts a resort for pulmonary invalids. In tropi- 



* Reprinted, by permission, from a " Text-Book of Geology," 

 by Archibald Geikie, LL.D. London : Macmillan & Co., 1882. 

 Pp. 971. 



