New York: Whittlesey House, 1930.
First Edition. Hardcover. Very good. xv, 320 pp, with color frontispiece, index, illustrations (from photos and drawings by the author), maps (one folding). Short tear in cloth along rear joint at head of spine, paper cracked over front hinge, occasional penciled lines in the margine; else sound and clean. No dust jacket. Willis was a mining engineer who worked for the U.S. Geological Survey. "In 1929, after attending an IGC conference in South Africa, Willis traveled the length of Africa, accompanied by his wife and supported by the Carnegie Institution of Washington, to study the geologic structure of the deep rift valleys that bisect the East African plateau. His study convinced him that the valleys had not developed because of separation, as most geologists thought, but were the result of "ramping" caused by compression and vertical movement" (ANB).