In the progress of geology the influence of climate has been one of the last great subjects to receive attention. During a residence of four years in the dry eastern part of Asiatic Turkey, from 1897 to 1901, the importance of climatic influences was impressed on me by the contrast between the topography and superficial deposits of that semi-arid region and those of the moister, glaciated portion of the United States. The impression was strengthened in 1902, when, as a member of a party under the leadership of Professor Davis, of Harvard University, I visited the arid region of Utah and Arizona. There, not only do the superficial deposits and topography bear the impress of prolonged aridity, but the wonderful cross-bedding of the white Colob sandstone and the red color of the underlying Kanab formation apparently point to the existence of still more arid conditions during the Mesozoic era. . . .