ARTESIAN FLOWS 



55 



Flowing water is not confined to wells penetrating definite 

 porous beds such as are shown in the figures. Bedding planes 

 (Fig. 4) in limestones and other rocks, joint planes in crystalline 

 rocks (Fig. 29), solution passages in limestone (Fig. 30), porous 

 (vesicular) layers of traps (Fig. 31), etc., all afford artesian flows 

 under favorable conditions. 



FIG. 29. Section illustrating artesian conditions in jointed crystalline rocks without 

 surface covering. A, C, flowing wells fed by joints; B, intermediate well between 

 A and C of greater depth, but with no water; D, deep well not encountering joints; 

 E, pump well adjacent to D, obtaining water at shallow depths; S, dry hole ad- 

 jacent to a spring, showing why wells near springs may fail to obtain water. 



FlG. 30. Section illustrating conditions of flow from solution passages in limestone. 

 A, Brecciated zone (due to caving of roof) serving as confining agent to waters 

 reached by well I ; B, silt deposit filling passage and acting as confining agent to 

 waters reached by well 2; C, surface debris clogging channel and confining waters 

 reached by well 3; D, pinching out of solution crevice resulting in confinement of 

 waters reached by well 4. 



Flows from Sands and Sandstones. It is the sands and sand- 

 stones that give rise to our great artesian systems. Often of great 

 thickness and extending without interruption for hundreds and 

 even thousands of miles, they are frequently saturated with 

 water under sufficient head to lift itself to the surface at scores of 

 points. It is such beds that give rise to the numberless flowing 

 wells along the river valleys, lowlands and shores of the Atlantic 

 Coastal Plain, to the great flows from the Dakota and other sand- 

 stones in portions of the High Plains along the east flanks of the 

 Rockies, and to flows in numerous other areas of less extent. 



