SUPERFICIAL DEPOSITS IN CVTCE. 183 



would be hemmed in by lofty hills into a gradually narrowing valley, so tliat 

 its force would be greatly increased. 



The lamination may, at first sight, seem a difficulty in the way of the 

 proposed explanation, but it is not so. The principal dust-bearing gales 

 are in the hot season, and these will leave a deposit of sand or calcareous 

 dust upon any pre-existing surface. Then the succeeding rains, which are 

 not often so heavy in Cutch as to wash such deposits away, will cement the 

 particles together at once as they do the flood-deposits along the river-sides. 

 Thus each lamina will represent a season's work. That the laminai should 

 dip towards the rock on which the concrete rests, on the side nearest to the 

 rock, is what we should expect in a wind-blown deposit. For when sand is 

 blown against an obstacle it is thrown back again, and the wind has to pass 

 away on either side, so that in such places we always find an intervening 

 valley between the mound and the obstacle, the surface of the mound thus 

 sloping towards the obstacle. 



The loose porous character of the deposits, as already pointed out, is 

 against their aqueous origin, but is what we should expect in an seolian 

 formation only so far subjected to water that it has been rained upon. The 

 uniformity of general character over a wide area, independently of the rock 

 below, is thus fully accounted for. The more calcareous composition of the 

 southern deposits is due to the fact that the materials here are mostly 

 derived from the sea (hence the miliolines,also), while farther north the dust 

 is reinforced by the breaking-up of the Jurassic sandstones. The enclosure 

 of the local rocks and of the local BuUminus is quite natural, the dust finding- 

 its way into the interstices of whatever was lying on the ground. 



{To be continued.) 

 [From the Journal of the Geological Society.'] 



