I didn't know Thomas is such a remarkable designer, I considered him as a leading beads collector only!

I wonder whether there is some additional info on these very interesting discoidal beads.
They seem to be made of carnelian and jasper, and I guess they are excavated, because the beads on one of the strands I own are encrusted with rusty iron to the point of some of them being glued together -- but how old?, belonging to which culture?, of African manufacture?