OUR WATER SUPPLY 



By Oscar E. Meinzer 

 United States Geological Survey 



GENERAL CONSIDERATIONS 



Water in relation to physical processes. — In the physical and bio- 

 logical evolution that has taken place on the face of the earth, water 

 has had a unique function as the principal vehicle for the transfer of 

 matter and energy. It appears that all evolution, whether physical or 

 biological, requires, on the one hand, sufficient rigidity to supply a 

 degree of stability and permanence, and on the other hand, sufficient 

 fluidity or plasticity to permit more or less gradual change in response 

 to applied energy. In the physical evolution of the earth there have 

 been two major complementary processes. One has been the repeated 

 raising of parts of the solid exterior of the earth to considerable eleva- 

 tions above sea level through deformation and the intrusion or 

 extrusion of fluid or plastic rock material; the other has been the 

 reduction and modification of the raised parts, chiefly, though not 

 exclusively, through the agency of the water acting in its role as the 

 transporter of matter and energy. Thus the development of the geo- 

 logic structure of the outer part of the earth and the creation and 

 re-creation of the land areas in all their characteristic detail, have been 

 accompUshed chiefly because the earth is surficiaUy rigid but funda- 

 mentally plastic, and because there is a supply of water which has 

 served as the principal agent in mechanical weathering, as the carrier 

 of oxygen and other elements that are active in chemical weathering, 

 and as the transporter of the weathered materials in suspension or 

 solution with subsequent deposition of these materials and forming 

 of the sedimentary deposits. 



Although the poet may regard mountains as the symbol of eternal 

 permanence, the geologist knows that they are ephemeral features 

 which stand majestically for but a brief period, only to disappear 

 under the erosive work of the water. To the geologist the work of the 

 water is almost everywhere in evidence — in the sculpture of the land, 

 in the character of the soil and subsoil, in the vast succession of sedi- 



• Address of the retiring president of the Washington Academy of Sciences delivered January 21, 1937. 

 Keprinted by permission from the Journal of the Washington Academy of Sciences, vol. 27, no. 3, March 

 15, 1937. 



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