CIRCULATION OF AQUEOUS SOLUTIONS. 1027 



move continuously downward from the place where it enters the rock to 

 where it issues from it. The form of the curved path is influenced by 

 many factors of which the increase in temperature with depth, limiting 

 formations, the preferential use of large channels, the relative lengths of 

 the vertical and horizontal components are the more important. 



The greater the temperature the less the viscosity of water. At 90° C. 

 the viscosity is only one-fifth as great as at 0° C, and at 300° C. the vis- 

 cosity may not be more than one-twentieth of the amount at 0° C. Since 

 the flowage in capillary openings, which is the prevalent abundant kind in 

 rocks, is inversely as the viscosity, the increase of temperature with depth 

 is plainly favorable to deep penetration. 



The movement of any aqueous circulation is practically stopped by 

 strata in which all or nearly all of the openings are subcapillary. In the 

 most favorable case for depth this would be the bottom of the zone of frac- 

 ture. In many cases, however, limiting strata are found at very moderate 

 depths, and there may be several limiting strata bounding pervious strata. 

 (See fig. 12.) In all such cases a given circulation is stopped by the lim- 

 iting strata, and the lines of flow are thus severely confined. The influence 

 of limiting impervious strata upon the ground-water circulation is well 

 illustrated by many of the artesian systems. Of the various combinations 

 which result in artesian flow a limiting impervious stratum above a per- 

 vious stratum is the most common. 



In general it may be said for a system of circulation that the entire 

 available cross section is utilized, but not uniformly. Other things being 

 equal, the more direct route is used to a greater extent than a less direct 

 one, and therefore the remoter corners of a water system may have rela- 

 tively small circulations. 



Since the vertical movement of ground water is at a maximum confined 

 to the zone of fracture, it can not exceed 10,000 or 12,000 meters, and 

 commonly is much less than this. Indeed, in many systems of circulation 

 the greater part of the water does not reach a depth as great as 1,000 

 meters. 



There is no assignable limit to the extent of the lateral movement, but 

 commonly it is longer than the vertical movement, in many cases hundreds 

 or thousands of times longer. For instance, in the artesian circulation of 

 the Dakota sandstone the horizontal journey of the water is at least from the 



