GEOLOGY IN EVERYDAY LIFE MANSFIELD 267 



mineral resources as coal, oil, natural gas, phosphate, and salines on 

 public lands, and the interest of the Nation as a whole in their proper 

 conservation and use was aroused. Congress passed legislation re- 

 serving mineral rights to the Government, setting up reserves for 

 special purposes, and providing for the lease and exploitation of 

 public mineral lands. A necessary corollary was the acquirement 

 of more precise information regarding such lands. The Geological 

 Survey thus began and has since continued systematic surveys to 

 show accurately the distribution of these minerals with respect to the 

 established subdivisions of the public land and to measure and sample 

 the deposits for purposes of computing reserves. The acreage with- 

 drawn from or restored to entry and the estimates of reserves have 

 been modified from time to time as new information has become 

 available. They have formed the basis of national planning and 

 legislation. Besides this, land classification data are extensively used 

 by the General Land Office in administering public lands. 



Water supplies. — In the better-watered parts of the United States 

 and other countries, questions of water supply have not, on the whole, 

 seemed serious until recent years. The situation is different in more 

 arid regions where water is the crux of the question, whether a given 

 area can be used agriculturally or industrially, or perhaps at all. 

 With the rapid expansion of cities in the more thickly settled areas 

 and the increased demands for water in some western States, questions 

 of water supply have assumed national importance. Investigations 

 and measurements must be made both of the available surface water 

 and of water in the ground. These are long-continuing projects 

 because rainfall, which controls both the surface and the ground sup- 

 ply, fluctuates so that investigations, covering only short periods, 

 are likely to be deceptive and undependable. 



The problems of proper development and utilization of water involve 

 the cooperation of the engineer, the geologist, and the chemist. The 

 engineer is concerned with its production or accumulation, its trans- 

 portation and handling as a commodity; the geologist with the 

 character (thickness, porosity, etc.) and position of the water-bearing 

 beds, their recharge from available rainfall and their possible con- 

 tamination by salt water or other undesirable substances. With the 

 engineer, he is concerned with the character and stability of rocks 

 affected by tunnels, aqueducts, dams, and other structures. The 

 chemist determines the quality of water as regards mineral and organic 

 content. Mineral water, through clogging or staining, may be injuri- 

 ous for industrial use. Mineral substances in solution may also affect 

 health. For example, fluorine detected in the waters of some of the 

 southwestern States has proved injurious to the enamel of human 

 teeth. Organic matter is deleterious to health. 



