erosion in one of its forms, water supplies have decreased either in moisture in the 

 upper layers of the soil owing to the lowering of the water table, thereby, affecting 

 wells; or decrease in, or cessation of, springs ; or disappearance of the water in 

 streams during the dry months of the year and lowering of the water level during the 

 same period in the smaller and larger rivers. The rainfall has also decreased in annual 

 amounts, though the amounts of such decrease may be slower in making their appear- 

 ance; but, more alarming, this rainfall has become capriciously intermittent in its sup- 

 plies — no man being able to forecast the amounts which will be obtained within the 

 year; or often, within limits, at what periods. 



This is not 'drought' in the ordinary accepted sense of that word. I would term it 

 the 'Intermittent Stage' in rainfall supplies. It may be suggested that if the fact of the 

 intermittency of the rainfall, developing at a certain stage in the degradation of the soil 

 and its covering, be accepted as a factor of importance in this decrease in fertility, we 

 can start from a point at which we all are voicing the same position of affairs and can 

 commence, according to the different types of erosion, the business of combating the 

 danger. Lavauden (Les Forets du Sahara) "wrote'ln the middle of the Quaternary period, an 

 epoch which it is impossible to date precisely, the Sahara was a very humid region, 

 the fluvial system was of a particularly powerful type, allied without doubt to very 

 abundant precipitations. Today all these river beds are dry, and only the largest retain 

 underground water of which the amounts constantly diminish — slowly perhaps but in- 

 evitably — owing to the equilibrium existing between the precipitation and evaporation. 

 An important question is to determine at what epoch the dis- equilibrium between the 

 two commenced to make itself felt; in other words at what period desiccation commen- 

 ced to become seriously apparent.' This represents exactly what I term 'Intermittent 

 Rainfall '. 



It may be asked 'How can this stage be recognised on the ground?' Examples are 

 only too plentiful. If we examine the regions bordering the southern edge of the Wes- 

 tern Sahara (British and French colonies) it will be found that a stage is reached in the 

 rainfall conditions where dependence upon them for crop production can no longer be 

 placed with ordinary confidence. For certain localities in Northern Nigeria and the 

 French Niger Colony the local population complain of violent winds which, blowing at 

 the beginning of the rainy season about May or June, bring blown sand on to their 

 fields. The millet crop is sown during the first rains. Should the previously normal 

 second rains arrive up to time, when the seedlings have shown above ground the roots 

 of the latter fix the sandy soil (it will be noted that there is already a sandy covering 

 blown from the adjacent Sahara Desert covering the normal soil surface) and the growth 

 of the crop proceeds successfully. Should the second and main rains not come up to 

 time, however, sand carried by the strong winds covers the seedlings and kills them. 

 The operation of sowing has then to be undertaken a second time and, maybe, a third or 

 fourth. Indeed cases are on record when the seed has been sown as many as ten times! 

 This example would appear to be a strong argument in favour of the postulate here ad- 

 vocated that a time arrives when the rainfall becomes intermittent and man can count no 

 further on its reliability. 



It has become apparent that in some quarters opinions are held that there can be 

 no analogies between, say, the desiccation being produced in parts of Africa and the 



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