Note 66 — PART III.

Pebble bands are occasionally met with in the coarser sandstones of the Fluvio-marine series, and it would seem that from them are derived the pebbles of quartz and flint which so invariably strew the desert-surface to the north to beyond the latitude of Cairo. Those flints on the surface are largely broken up and flaked by changes of temperature, but show comparatively little shaping by blown sand; the white quartz pebbles on the other hand, while seldom or never broken or flaked, are invariably more or less facetted, frequently into typical “dreikanter” or pyramid-pebbles; below the surface both varieties are perfectly water-rounded.