BRIEF COMMUNICATIONS 359the obsidian found in Upper Egypt came from mines situated less than 250 km from Porc Epic, in the Ethiopian Rift Valley. The provenance of the obsidian as supported by this study together with chemical data from Eritrean obsidian permits to conclude that overland exchange routes through the Gash Delta are more likely than maritime routes involving the Red Sea and the coast of Eritrea and the Arabian Peninsula. Exchange would thus follow a 'down-the-line' model, whose links would include the Gash Delta and the Nubian A-Group, although the number of obsidian samples excavated between Ethiopia and Egypt is currently too low to arrive at reliable conclusions.