The Nejd is crossed by several ridges of which the best known is Jebel Shammar running nearly east and west at an altitude of about 6,000 feet. Jebel Menakib, Jebel Aared, Jebel Toweyk and Jebel Athal are other ranges south of Jebel Shammar and also running in a similar direction toward the southwest and northeast. The Sinai peninsula is a rocky limestone plateau intersected by rugged gorges and highest toward the south in the region of Sinai proper. Next to its wadys and mountains Arabia is characterized chiefly by the so-called _Harrat_ or volcanic tracks already mentioned. These black, gloomy, barren regions occupy a much wider extent of north Arabia than is generally supposed. The largest is _Harrat Khaibar_, north of Medina, the old centre of the Jews in the days of Mohammed. It is over 100 miles in length and in some parts thirty miles wide. A wilderness of lava and lava-stones with many extinct crater heads, craggy, and strewn with rough blocks of basalt and other igneous rocks. In some places the lava beds are 600 feet deep. Signs of volcanic action are still seen at Khaibar, smoke issuing from crevices and steam from the summit of Jebel Ethnan. A volcanic eruption was seen at Medina as late as 1256 A.D.[2] and the hot and sulphur springs of Hasa and Hadramaut seem to indicate present volcanic action. The sandy-tracts of the so-called Arabian deserts are termed by the Arabs themselves _nefud_ (drained, exhausted, spent), the name given on most maps. The general physical features of this “desert” are those of a plain clothed with stunted, aromatic shrubs of many varieties, but their value as pasture is very unequal, some being excellent for camels and sheep, others absolutely worthless. Some nefuds abound in grasses and flowering plants after the early rains, and then the desert “blossoms like the rose.” Others are without rain and barren all year; they are covered with long stretches of drift-sand, carried about by the wind and tossed in billows on the weather side of the rocks and bushes.[3] Palgrave asserts that some of the nefud sands are 600 feet deep. They prevail in the vast unexplored region south of Nejd and north of Hadramaut including the so-called “Great Arabian Desert.” Absolute sterility is the dominant feature here, whereas the northern nefuds are the pasture lands for thousands of horses and sheep. [Illustration: PTOLEMAEUS KARTE VON ARABIA FELI] II THE GEOGRAPHICAL DIVISIONS OF ARABIA