CONSOLIDATION OF UNSTABLE HILLSIDES. 233 



roots about a foot long are buried in pits from 4 to 5 feet deep and 

 watered every fourth day during the dry season. At the end of 

 their fourth year the suckers that come up are 12 to 20 feet 

 high. Prosopis gpieigera, being a desert species and also able 

 to throw up root suckers, will probably succeed better than sissu. 



In more extensive areas than those at Jeypur it may be found 

 necessary, at the same time that planting is begun on the wind- 

 struck edge of the desert to stop inroads of the sand beyond the 

 opposite edge by forming a special barrier similar to the littoral 

 dune in operations on the sea-coast. In connection with the lor- 

 mation of such barriers it is necessary to mention a most remark- 

 able fact observed in the second or Motidongri tract at Jeypur. 

 The sand does not only drift along the surface of the ground, but 

 is also blown through the air in large quantities, even over 

 obstacles (such as a ridge) more than 300 feet high. If there is 

 another similar obstruction parallel to the first and not more than a 

 few hundred yards off, most of the sand that comes over this first 

 barrier is deposited between both, especially on the reverse face 

 of the former ; otherwise the sand is carried away to great 

 distances and is distributed over so large an area as not to visibly 

 affect its surface in any way. Another remarkable fact deserv- 

 ing to be recorded is that when a very high obstruction, such as 

 a lofty ridge, is encountered, the sand, after striking against it, is 

 thrown back and forms a distinct lower parallel ridge (dune) 

 some distance in front of it. At Jeypur there is such a dune 

 about 300 feet high in front of the great Nahargarh ridge. 



SECTION III. 



Consolidation of unstable slopes. 

 Very little has yet been done in India to rewood bare slopes 

 prone to erosion and landslips, and the little that has been attempt- 

 ed has been confined to areas where denudation is a compara- 

 tively gradual process. Hence here also we have hardly any local 

 experience to guide us in dealing with cases of a serious character. 

 In the absence of such experience, the following observations, 

 based chiefly on the knowledge gained in the execution of the 

 reboisement works carried on with such marvellous success in the 

 French Alps, may prove useful as suggestions. 



ARTICLE 1. 

 Causes of benudation of hillsides. 

 Slopes may become unstable owing to the action of several or 

 all of the following causes ; — 



