THE CAMPS ON THE VAAL	149
	This washing machine was practically the same as the Aus­tralian gold placer miner's cradle, or the American rocker, and it had been used for years on the Brazilian diamond fields, though the screening of the Vaal was probably more exact. But the Brazilian negroes had become far more expert by long practice and training than the green workers on the line of the Vaal, and the handling of the concentrate in their bateas was extraordinarily deft. It has been demonstrated over and over again in placer fields that inexperienced washers cannot compete with trained hands in concentrating gold dust, and even expert gold placer workers often failed to handle diamond-bearing gravel efficiently. So it is not surprising that many of the awkward adventurers in the new fields lost heart completely at their failure to extract any diamond from the masses of gravel which they dug and washed so laboriously ; and it is practically certain that the per­centage of gems saved, at first, was below the average winning from the Brazilian sands. The irregularity of the distribution of diamonds in the shore bed was greatly perplexing and disappointing to the groping locaters. The precious stones were strewed in the gravel in a scattering way that defied any calculation. Here and there was a rich patch of ground, while tracts all around it, precisely simi­lar in a surface view, held only a few small diamonds or were