The range from the same point of view presents a singularly uniform outline, having the appearance of an unbroken wall; in reality, however, it is traversed by a number of deep ravines (wadis), of which the most important are the Yabis, the Ajlun, the Rajib, the Zerka (Jabbok), the Hesban, and the Zerka Ma`in.
At the period of the Israelite conquest the portion of Gilead northward of the Jabbok (Zerka) belonged to the dominions of Og, king of Bashan, while the southern half was ruled by Sihon, king of the Amorites, having been at an earlier date wrested from Moab (Numb.
They are distributed along both banks of the Kerwan, a brook which flows south through the Wadi-ed-Der to join the Zerka or Jabbok; but all the principal buildings are situated on the level ground to the right of the stream.
Now nothing is known of the occurrence of such in Arabia, but a few specimens of rather small size seem still to exist in Syria, in the Wadi Zerka, an eastern tributary of the Jordan.
Among the perennial streams may be mentioned the Na'aman, south of Acre; the Mukatta` Kishon, at Haifa; the Nahr ez-Zerka, sometimes called the Crocodile River - so named from the crocodiles still occasionally to be seen in it; the Nahr el-Falik; the `Aujeh a few miles north of Jaffa and the Nahr Rubin.
Two great rivers, the Yarmuk (Hieromax) and the Zerka (Jabbok), divide Eastern Palestine into three sections, namely Hauran (Bashan, q.v.) with the Jaulan west of it; Jebel Ajlun (Gilead, q.v.); and the Belk'a (the southern portion of Gilead and the ancient territory of the tribe of Reuben).
South of the Zerka the country culminates in Jebel `Osha, a peak of Jebel Jil`ad (" the mountain of Gilead "), 359 6 ft.
The spring of the Zerka Main (Calirrhoe) has a temperature of 142° F.