INTRODUCTION. 212 



easily recognised, both by the abundance of reeds and by the presence 

 of crocodile, which can be seen in swarms. 



In this Nara belt the brackish dhands of Khairpur are alkaline ; 

 those of Khipro are saline, while those of the Sanghar taluqa are 

 of an intermediate type. The alkaline dhands can be distinguished 

 even at a distance from the saline. Round the shores of the alkaline 

 dhands and some little way into the dhand, there is abundant soft 

 "reen iirass, and abundant trees. The saline dhands are barren 

 of grass, and except for a few halophytes such as tamarisk and 

 saltworts, are very bare of trees. Small tamarisk bushes are 

 however very common round the saline dhands, and their presence 

 accounts for the very curious shapes of the hillocks of gypsum 

 (chiroli) seen all round the shores of these dhands. It is well known 

 that the tamarisk grows in places which are liable to be submerged 

 in time of flood. Those which now grow on the shore of the dhands, 

 were in former days liable to be completely submerged by floods, 

 or may have been continually partially under water. The saline 

 dhands have deposited great quantities of gypsum as well as salt, 

 and it is clear that amongst other constituents of the salts washed 

 into these dhands sulphate of calcium was abundant. The gypsum 

 crystallises around the stems of the tamarisk. I have collected 

 specimens of gypsum growing round branches of dead tamarisk 

 from some of these dhands. The crystals are disposed radially 

 around the branches of the tamarisk, so that the stems become 

 thickened with a casing of white crystals of gypsum. The tree 

 now looks like a tree covered with hoar-frost and frozen hard. 

 The process of deposition of gypsum goes on, until the resemblance 

 to a tree is lost, instead of a tree there is a small round hillock with 

 innumerable rounded knobs. The cylinders of gypsum which 

 surrounded the branches have broadened and coalesced until this 

 curious shape is arrived at. If one of the knobs is broken off the 

 remains of the decayed tamarisk stem will be found in the middle, 

 and the crystals will be observed to radiate out from this central 

 stem. Both stages of development are shown in Plate 13. 



These mounds of chiroli (gypsum) are characteristic only of 

 saline dhands. It is easy to see that in the presence of sodium 

 carbonate, any calcium sulphate present would be precipitated as 

 carbonate ; hence no gypsum is found near the alkaline dhands. 



It has been said that the alkaline dhands support a more luxuriant 

 vegetation than the saline ; they have other distinct characteristics. 



