. Discovery. Science. DISCOVERY 269 The stream-washing is much more simple and methodical. The stream-bed consists wholly of well water-worn granite, and of boulders and pebbles of gneiss and garnetiferous granite ; below the surface- layer the boulders and pebbles are embedded in latterite, much decomposed and with a considerable quantity of kaoline ; it is in this that the gems are found. The process of recovery is by washing in a conical-shaped basket made of cane, about 2 ft. in diameter at the top and 12 in. deep to the apex of the cone. A curious feature of these baskets is that they are
. Discovery. Science. DISCOVERY 269 The stream-washing is much more simple and methodical. The stream-bed consists wholly of well water-worn granite, and of boulders and pebbles of gneiss and garnetiferous granite ; below the surface- layer the boulders and pebbles are embedded in latterite, much decomposed and with a considerable quantity of kaoline ; it is in this that the gems are found. The process of recovery is by washing in a conical-shaped basket made of cane, about 2 ft. in diameter at the top and 12 in. deep to the apex of the cone. A curious feature of these baskets is that they are water-tight. They hold about 30 lb. of wash- gravel : the gravel is placed in the basket, which is then filled with water by submersion ; a rotary and at the same time a tilting motion is applied, which causes the lighter particles to come to the surface and pass out over the basket edge. This process is repeated until only a small quantity of the wash-gravel con- centrates are left in the cone of the basket. This is then dumped on to a mat and hand-picked for any gems it may contain. All natives in the gem-districts are expert gemmers in their own crude way. The men and boys generally do the digging ; the women are certainly the best washers I have ever seen ; in fact, they can get a perfect concentrate either by washing with water or by dry-vanning. In dry-vanning they use a basket made like a housemaid's dusting-pan, and by dexterously throwing up the gravel repeatedly in the air and with a jerk, they pass all material of light specific gravity on to the ground and collect the heavy concentrates at the base of the basket. Impressed with the expertness of the vanning, I made a test of gems from three separate minerals, thorianite, and ordinary gravel. The vanner never lost a single gem or thorianite crystal, and then, to show how expert she was at her job, separated the gems from the thorianite. Fig. 2 shows this woman at work on this actual vanning test. I have just said th
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