The countries of the Middle East (Fig. 1.1), the region reviewed in this book, cover parts of the lands of the eastern Mediterranean and the greater part of Arabia (Arabian Shield, Arabian Platform and Arabian Gulf), and the western Zagros Thrust Zone, an area enclosed between 13 ° and 38 ° N and 35 ° and 60 ° E (Figs. 1.2 and 1.3). Topographically, the higher elevations generally lie to the west in the Arabian Shield and pass eastward into the lower-lying areas occupied by the Arabian (Persian) Gulf and the Tigris-Euphrates Valley.