was exhibited on the streets of zanzibar , and all said it had come from the interior , where the ruins of a city called zinj may be found , and it is here that such diamonds may be found in profusion , scattered upon the ground and also in rivers in 1334 , another arab , ibn mohammed , stated that `` our number made arrangements to seek out the city of zinj , but quitted our quest upon learning that the city was long since abandoned , and much ruined .