CONTROLLING FACTORS OF ARTESIAN FLOWS 627 



Page 



Requisites of artesian flows » 631 



Objections to common requisites • • 631 



Chamberlin's requisite conditions of artesian flows 631 



Pervious stratum 632 



Impervious bed below 632 



Impervious bed above • 632 



Inclination of beds 632 



Outcrop of porous stratum 633 



Adequate rainfall 633 



Points of escape 633 



Essentials of artesian flows 633 



Modifying factors 634 



Secondary factors of artesian flows 634 



Introduction 



It is uow more than twenty years since the publication of the admirable 

 paper by Professor T. C. Chamberlin on the "Requisite and qualifying condi- 

 tions of artesian wells,"t during which period it has remained the standard 

 in this country. It deals, however, almost entirely with the porous bedded 

 rocks, such as sandstones, taking little account of the drift or limestones, 

 and practically none at all of the crystalline rocks. Late investigations, 

 especially in the East, and the growing demand for ground water for industrial 

 and public purposes or for summer resort supplies have led to a very ex- 

 tensive development of wells in each of the classes of material mentioned, and 

 have shown their great economic as well as scientific importance, emphasizing 

 the need of a reexamination into the requisites of artesian flow and a dis- 

 cussion of their controlling and modifying factors. 



In view of the number of different ways in which the term artesian has 

 been used in the past, it will not be out of place to state that in the present 

 paper the term is applied in the sense adopted by the United States Geological 

 Survey after consultation with leading geologists of the country, namely, 

 to designate the hydrostatic principle by which confined waters tend to rise 

 in virtue of the pressure of the overlying water column, irrespective of whether 

 or not this pressure is sufficient to lift the water to the surface and produce 

 a flow.* 



Artesian flows may be said to depend upon the nature of the reservoirs, 

 the conditions of confinement, and tlie sources of the water. An enumeration 

 of the factors are given below. 



Undekgkound Water Reservoirs 



By an underground water reservoir is meant the opening or system of 

 openings within the rocks in which the water is contained. The more im- 

 portant types may be summarized as follows : 



Types of Water Reservoirs 

 I. Original forms. 



1. Original pores. 



t Fifth Annual Report U. S. Geological Survey, 1S85, pp. 125-173. 



* M. L. Fuller : Significance of tlie term "Artesian." Water supply and irrigation 

 paper no. IGO, 1900, pp. 9-15. 



