630 PKOCEEDIXGS OF THE KEAV YORK MEETING 



6. Confined air and gas. 



7. Fresh water. 



8. Salt water. 



B. Lower confining agents. 



1. Impervious beds. 



2. Stratification. 



3. Friction. 



4. Mineral crusts. 



5. FrOst zones. 



6. Confined air and gas. 



7. Fresh water. 

 .8. Salt water. 



9. Cementation. 



10. Heat. 



11. Pressure. 



II. Jointed and fractured roclis. 



A. Upper confining agents. 



1. Impervious hanging wall. 



2. Impervioiis surface coverings. 



3. Frost fillings. 



4. Vein fillings. 



5. Weathering products. 



6. Converging walls. 



7. Interrupted joints. 



8. Sea water. 



B. Lower confining agents. 



1. Impervious footwalls. 



2. Vein fillings and cementation. 



3. Converging walls. 



4. Interrupted joints. 



5. Fresh water. 



6. Sea water. 



7. Heat. 



8. Pressure. 



Nature of Artesian Circulation 



Artesian circulation takes place by virtue of the variations of pressure to 

 which the water is subjected in different parts of its reservoirs.- By definition 

 of the artesian principle, all but hydrostatic pi'essure is excluded as a deter- 

 mining cause of circulation. There are, nevertheless, a number of modifying 

 agencies which in cases exert a powerful influence on the water-head and 

 movements. The more important of the controlling factors may be summarized 

 as follows: 



Factors in Artesian Circulation 



Primary factors. 



Gravity (hydrostatic pressure). 



J 



