THE SOIL AND WATERCOURSES 45 



and so consolidated, there is no subsoil drainage. 

 One finds therefore that some degree of saltness 

 is characteristic of flat clay or mud deserts. In 

 the parts which lie a little higher than the rest, 

 and from which the salt is washed by the rain, 

 the salinity is slight, and plants, many of them 

 specially adapted to growth in salt places, may be 

 found. In the depressions it is common to find 

 an incrustation of crystals of salts, and an absence 

 of vegetation of any kind whatsoever (Fig. 14), 

 or one may find that the ground is slimy, even in 

 dry weather, owing to the hygroscopic properties of 

 the salts which it contains. Around the margins 

 of these salt patches one finds an intermediate 

 zone inhabited by salt-loving plants, such as grow 

 at home on sea marshes. In Fig. 14 the plants 

 on the right are Suaeda : they are growing on land 

 which is a few inches higher than that on the left, 

 which is covered with white salt-crystals. Fig. 15 

 shows Atriplex halimus and other bushes which 

 love salt, growing on a plain of salt mud. 



The salts found in these positions vary. Common 

 salt (sodium chloride) is, I believe, always present, 

 but in less proportionate amounts than in sea water. 

 In Transcaspia magnesium and sodium sulphate 

 are common, and calcium sulphate (gypsum) occurs. 

 In Mesopotamia different proportions of chlorides 

 and sulphates of sodium, calcium,, and magnesium 

 all occur in relatively large quantities, in the salt 

 and alkaline lands. 



Figs. 16 and 17 show a peculiar type of salt 

 clay desert which is found at the lower end of the 



