CLASSIFICATION OF SPRINGS 553 



springs (Fig. 18 c). Though rare, springs of this class occur in till, 

 and doubtless examples may be found in other t3rpes of rock. 



The springs of the three classes just described depend on the 

 outcrop of the saturated porous bed in its lower portion. Springs 

 occurring where the porous bed does not crop out, but the water 

 escapes from it by an opening leading to the surface, may be 

 termed fracture artesian springs (Fig. 18 J). Many of these 

 springs have been classed with fissure springs, but it seems essential 

 to distinguish between springs that tap artesian basins and yield 

 water under hydrostatic head, and those that depend on the deeper 

 waters of the crust. This name is chosen because it seems probable 

 that all such openings are primarily fractures in the rocks. Although 

 it is true that great pressure is exerted by the water in deep artesian 

 basins, it seems improbable that pressure could force water to rise 

 through overlying material in sufficiently definite channels to 

 supply springs unless it moved along pre-existing faults or other 

 fractures. Water pressure may assist in keeping the fracture open, 

 and the flow of water tends to plaster up caving walls with mud, 

 as in the hydraulic systems of drilling wells, or to solidify them with 

 precipitated minerals. Many of the springs of this class have a 

 high temperature, a steady flow, and an alignment that causes 

 them to be confused with true fault springs. However, a dis- 

 tinction should be made. If definite artesian structure can be 

 demonstrated, most of the water is probably meteoric in origin — 

 that is, it is derived from rain or melted snow absorbed at the out- 

 crop; if artesian structure cannot be demonstrated, there is a 

 strong presumption that much of the water arising along great 

 faults and deep fractures in the crust is of juvenile origin — -that is, 

 it issues from deep within the earth and now sees the light of day 

 for the first time. At any rate, there is a sufficiently distinct 

 difference in structure to justify separate classification of the 

 springs. 



In Antelope Valley, California, porous sand and gravel under- 

 lying clay contain water under artesian pressure. Numerous wells 

 have been sunk to obtain this water, and its chemical character 

 and temperature are known. Buckhorn, Indian, Willow, and 

 other springs having water similar in character and temperature 



