stones, gold and silver, lead and copper, lapis lazuli and carnelian. From them also, thrust up in the wake of the volcanic activity of late Pliocene times, came diorite and obsidian, both highly prized in antiquity. Finally, the rivers of Iran, racing swiftly through tremendous defiles from the heights to level land, brought fertility to many thousand square miles of barren soil, and desolation to other thousands. Silt carried by these streams during the glacial or pluvial periods was deposited in an inner basin and covered with water which evaporated as the winds swept together the sandy gravel. Thus, what was once a mighty sea became only sandy wastes and salt deserts. By far the greater portion of Iran is desert throughout the year, while, as summer advances, large tracts which in the spring were green are burned up and the whole plateau becomes dry and parched.
Judged on this basis, the land might truly be thought forbidding and uninviting to foreigners. Nevertheless, it is the connecting link between the Far East and the Near East. Migratory movements and warriors' campaigns have frequently swept across its borders in historic times, and these surely began in the dark past of prehistory. Consequently, the routes which lead without great difficulty into the land are worthy of special consideration.
Two passes across the Caucasus lead through Armenia into Anatolia, but a third permits entry to the coastal region south of the Caspian or to the
