[In] the highlands of the central Sahara beyond the Libyan desert,... in the great massifs of the Tibesti and the Hoggar, the mountaintops, today bare rock, were covered at this period with forests of oak and walnut, lime, alder and elm. The lower slopes, together with those of the supporting bastions — the Tassili and the Acacus to the north, Ennedi and Air to the south — carried olive, juniper and Aleppo pine. In the valleys, perennially flowing rivers teemed with fish and were bordered by seed-bearing grasslands.[2]