abstracts: hydrology 197 



point the Paleozoic formations seem to dip from the east, north, and 

 west. According to the interpretations that are made, the Pennsyl- 

 vanian series is 1400 feet thick in the southwestern part of the State and 

 extends more than 300 feet below sea level. 



The underground waters in the northeastern part of the State, where 

 older Paleozoic formations outcrop, have low mineralization, the total 

 solids generally being less than 500 parts per miflion, whereas in the 

 other parts of the State, where Pennsylvanian and Upper Cretaceous 

 rocks occur, the underground waters are generally highly mineralized. 



0. E. M. 



HYDROLOGY. — Geology and water resources of Sulphur Spring Valley, 

 Arizona. 0. E. Meinzer and F. C. Kelton. With a section 

 on agriculture by R. H. Forbes. U. S. Geological Survey Water- 

 Supply Paper No. 320. Pp. 231, with maps, views, and other 

 illustrations. 1913. (Also pubHshed as a bulletin of the Arizona 

 Agricultural Experiment Station.) 

 Sulphur Spring Valley is bordered by ranges in which are found pre- 

 Cambrian schist Paleozoic quartzites and limestones, Cretaceous sedi- 

 mentary rocks, and large masses of igneous and pyrociastic rocks, 

 chiefly acidic lavas of Tertiary age. The valley is underlain by Quater- 

 nary sediments correlated with the Gila conglomerate and shown by 

 well sections to be more than 1000 feet thick. Interbedded with the 

 Quaternary stream deposits is a clay bed at least 200 feet thick, cor- 

 related with similar stratified beds in other valleys of southeastern 

 Arizona, indicating a lake stage or general submergence probably early 

 in the Pleistocene epoch. Later in the Pleistocene the valley contained 

 a lake of 120 square miles, as is shown by 33 miles of well-developed 

 beach ridges. Beds of basalt interbedded with stream deposits indicate 

 two epochs of volcanic eruption during the Pleistocene. 



The valley sediments contain a main body of ground water and 

 smaller bodies of perched water. The ground water is derived from the 

 drainage of adjacent mountains and is returned to the atmosphere 

 through capillary rise over extensive alkali flats. 



As shown by maps with lines of equal minerahzation, the mineral 

 content of the ground water is related to the character of the rocks in 

 the adjacent mountains. Sodium carbonate waters having less than 200 

 parts per milHon of total solids are found adjacent to mountains com- 

 posed of igneous rocks. The soluble salts tend to become concentrated 

 near the surface by capillary rise and evaporation, but salt accumu- 

 lations have in some places been buried under clastic sediments. 



