40 LA TOUCHE: GEOLOGY OF WESTERN RAJPUTANA. 



from this bed (No. 3'285) a is coloured a bright yellow by iron oxide, 

 and many of the foraminifera found in the sand have a similar colour. 

 Most of these interesting little fossils are flatly coiled shells probably 

 belonging to the genera Rotalia or Pulvinulina, but they have not yet 

 been accurately determined. I think that there can be little doubt that 

 these particles of carbonate of lime have actually been carried by the 

 winds from Cutch and distributed over the desert. The most distant 

 locality to which I have traced them is Khari, 40 miles to the north- 

 east of Bikanir and 500 miles from Cutch. Here they are exceedingly 

 minute and are not recognisable as foraminifera, but that is not to be 

 wondered at, considering that they have travelled so far in com- 

 pany with hard grains of quartz and other minerals. 



I found, on examining samples of the sand from several localities 

 with the microscope, that the great majority of the grains show little 

 or no signs of attrition, and are in fact for the most part as sharp and 

 angular as when they were broken off the parent rock. The contrast 

 between the effects of water and wind action is well brought out in 

 the sample from Teori, referred to above, in which the ordinary dune 

 sand is mingled with grains derived from the plateau of Vindhyan 

 sandstone to the south. The latter are easily recognisable under the 

 microscope by their bright red colour, and are all well rounded, having 

 been derived from an aqueously formed sandstone, whereas the grains 

 of dune sand are mostly quite angular. Such sand as this could never 

 form beds of sandstone with well rounded grains, like the " millet 

 setd" Triassic sandstones in England, which have been attributed to 

 the action of wind. 3 No doubt the fact that the grains of sand, when 

 driven by the wind, are all moving in the same direction with a more 

 or less uniform velocity, coupled with the minuteness of the grains, 

 which must make the effect of any collisions that may take place 



1 This number refers to the entry in the Rock Register of the Indian 

 Museum. 



2 See the discussion on a paper by Mr. Vaughan Cornish. '* On the forma • 

 tion of sand dunes." Geographical Journal, Vol. IX, p. 302. 



( 40 ) 



