1876.] of the Great Indian Desert. 97 



Except near Balmir, where there ai'e some craggy hills of ancient formations, 

 and where the sandstones of Mesozoic age resting upon the older rocks dip at 

 high angles, the sedimentary heels found preserve almost perfect horizon- 

 tally. The low cliffs of sandstone near Jodhpur, and those of sandstone 

 and limestone near Jaysalmir, are palpably scarps of subaerial denudation, 

 for they correspond precisely, over miles of country, to the outcrop of the 

 harder beds ; nowhere is a characteristic marine cliff, cutting through differ- 

 ent strata, to be met with, nor is there any evidence of marine action, so 

 far as I can see, around the isolated hills of Balmir. Whilst therefore 

 there is a probability that the sea did extend up the Indus valley and a 

 possibility that it may have stretched up the Liini basin, and from one side 

 or the other have reached the Sarnbhar salt lake, there is no evidence that 

 it covered in recent times the central area of the desert about Balmir and 

 Jaysalmir. 



§ 11. Nature and Origin of the Sand-hills. — I have already described 

 the general distribution of the sand-hills, and I have said that I am unable 

 to coincide with Sir Bartle Frere's views as to their origin. He compares 

 them to the ridges of rock found in Sind, and suggests that they may be due 

 to earthquake-action. He points out that the Allah Bund, which is known 

 to have been caused by an earthquake, is " a perfect outlying specimen of a 

 typical Thar sand billow of moderate height", and he discusses the mode of 

 formation of sand-ridges by the wind and gives his reasons for believing 

 that the ridges of the Thar are not due to wind-action. To some of these 

 reasons I shall revert presently. Meantime, I think Sir B. Frere has over- 

 looked some phenomena of sand-hill formation. At the same time none 

 of the works I have been able to consult throw any light upon the parallel 

 sand-ridges of the Thar, of which I confess I am unable to offer a satisfac- 

 tory explanation. I think, however, that there can be no doubt that all are 

 due to wind-action alone, and I will give my reasons after describing the 

 peculiarities presented. 



The sand consists chiefly of small grains of quartz, mixed with felspar 

 and hornblend in smaller proportions, other minerals only occasionally oc- 

 curring. The grains are mostly rounded, precisely as in the sand of rivers 

 or of the coast, and they are tolerably uniform in size. 



I have already mentioned that the sand-hills form long ridges, with a 

 very uniform general direction, along the edge of the Indus alluvium, where 

 they are highest, and where the country is completely covered by sand, and 

 that they are less regular in their direction more to the eastward. But 

 there is one character which they preserve in both localities, though it is 

 much more strongly marked to the eastward, and this is a tendency to ter- 

 minate abruptly with a steep face towards the north-east. The long north- 

 east to south-west ridges have as nearly as possible the same slope on both 



