National Geographic : 1952 Aug
channels. Most of our large springs are in northern Flor ida, the Missouri Ozarks, central Texas, the Snake River Plain of Idaho, western Oregon, northern California, and central Montana. Hot springs are formed by ground water that has come in contact with hot subter ranean rocks. Geysers erupt ing periodically, like Old Faithful in Yellowstone Na tional Park, spring from ground water collecting in underground chambers until it grows so hot that steam pressure sends a jet high into the air. Ground water is preferred for many purposes, because it is generally pure and free from sediment and comes out at a uniform tempera ture, an important factor in industrial use. Water from underground is used for drinking by about half the people in the United States. Taking too much water out of the ground may cause more than just a water scar city. Mexico City is built on top of a subterranean reser voir; as wells draw out more and more water, the entire city is slowly sinking.* There are similar spots in the United States where the land has sunk as much as eight feet. Does "Seeding" Make Rain? Many a farmer and rancher, his fields and pas tures parched for lack of rain, has watched with angry frustration as fleecy white clouds drifted overhead but no rain fell. Today most experts agree that it is possible, under the right conditions, to help Na ture make rain. Some scien tists assert they have made clouds give up rain or snow by "seeding" them either with dry-ice particles scat tered from airplanes or with silver iodide smoke generated * See "Mexico's Booming Capi tal," by Mason Sutherland, NATIONAL GEOGRAPHIC MAGAZINE, December, 1951. 279 The Oriental Institute Armageddon of Biblical Fame Drew Water from This Spring Women living near the Old Testament's famous battleground climbed 120 feet up and down the winding stairway at extreme right to get their daily ration. Here men working for the Oriental Institute form a basket brigade to excavate the ruin. This ancient engineering work proved to be the largest of its kind in Palestine.