What's Bred in the Bone by Grant Allen

Three weeks later, two torn and tattered, half-starved Europeans sat under a burning South African sun by the dry bed of a shrunken summer torrent. It was in the depths of Namaqua land, among the stony Karoo; and the fugitives were straggling, helplessly and hopelessly, seaward, thirsty and weary, through a half-hostile country, making their marches as best they could at dead of night and resting by day where the natives would permit them.

Their commissariat had indeed been a lean and hungry one. Though they carried many thousand pounds' worth of diamonds about their persons, they had nothing negotiable with which to buy food or shelter from the uncivilized Namaquas. Ivory, cloth, and beads were the currency of the country. No native thereabouts would look for a moment at their little round nobs of water-worn pebbles. The fame of the diamond fields hadn't penetrated as yet so far west in the land as to have reached to the huts of the savage Namaquas.