RECENT DEPOSITS. 39 



those samples which were collected near the eastern margin of the 

 desert where there are outcrops of micaceous schists and granites. 

 The rocks in the interior of the desert, on the other hand, the Malani 

 lavas and Siwana granite, do not contain mica, and its absence from 

 the sand, contrasted with the presence in abundance of the minerals 

 that are found in these rocks, is almost complete proof that the sand 

 has mainly been derived from local degradation of the rocks, and has 

 not, or at any rate the bulk of it, been transported from outside the 

 desert area. 



At the same time there is very good evidence that the sand is not 

 entirely of local origin, but that some of it has travelled from a con- 

 siderable distance. In all the samples that I have collected, including 

 localities so far apart as those south of Barmer and north-east of 

 Bikanir. there is an appreciable quantity of particles of carbonate of 

 lime which cannot have been derived from any of the local rocks. 

 Their amount varies from less than one per cent, in the sand from 

 Bikanir to as much as ten per cent, by weight in some of the samples 

 from the south-west, or from 251b to over 3 cwt per ton of sand. 

 But the most interesting point about these particles is that many of 

 them are casts of the shells of minute foraminifera, and this fact 

 affords a clue to their origin, I found that they were not the shells 

 of recent foraminifera blown up from the coast, but that they are in a 

 fossilised condition, for when they are immersed in weak acid on a 

 glass slip beneath the microscope, they dissolve away gradually 

 becoming smaller and smaller till at last nothing is left, and it is 

 evident that they are solid all through. I then examined a few speci- 

 mens of Tertiary limestones that had been collected in Cutch by 

 Messrs. Wynne and Fedden, and found similar foraminifera in some 

 of them, especially in a limestone almost entirely made up of frag- 

 ments of nummulites and other foraminifera, labelled as occurring 

 " North of Kannai, north-east of Teyrah, probably on the horizon of 

 the Gaj (Miocene) group of Sind." The specimen in the museum 



( 39 ) 



