572 A TREATISE ON METAMORPH1SM. 



enormous — to be measured in tens of thousands, and probably hundreds 

 of thousands of cubic kilometers. The amount of silica which the waters of 

 mineral springs carry is, on the average, less than 2 parts in 100,000. In 

 only a few cases is the amount greater than 10 parts in 100,000, although 

 in one case, that of San Bernardino spring of California, the amount runs 

 as high as 22 parts in 100,000." Supposing the amount of silica deposited 

 by underground waters to be as high, on the average, as 1 part in 100,000 

 (and the amount deposited is invariably less than that in solution), it would 

 be necessary to believe that over 260,000 times as much water must have 

 circulated through the sandstone formations as the enormous amount of 

 quartz which lias been deposited. The amount of silica assumed to be 

 deposited by underground waters may be too great or too small, but it is 

 certain that many thousand times as much water as deposited quartz has 

 circulated through the rocks. 



CHARACTER OF CIRCULATION. 



It has already been explained that the complex movements of ground 

 water may be resolved into two components, horizontal or lateral move- 

 ments and vertical movements. In order to understand the work clone by 

 underground water in its journey, it is first necessary to know the path 

 which it follows. On this point the recent analytical work of Prof. C. S. 

 Slichtef gives the desired information.'' According to Professor Slichter's 

 analysis, the flowage of water from one place to another through a 

 homogeneous medium, say from A to B, is not by a direct path, but by a 

 large number of diverging paths from A during the first part of the journey, 

 and by a large number of converging paths to B during the latter part of 

 the journey. This may be illustrated by supposing the water to be poured 

 into a well, A, and to flow to a well, B. The horizontal course of the water 

 is represented by fig. 7, and the vertical course by fig. 8. These conclusions 

 apply equally well to any porous rock, such as a soil or sandstone in which 

 the spaces are distributed in a somewhat uniform manner. 



It is apparent that Slichter's conclusions have far-reaching consequences 

 as to the flowage of ground water. In the passage of the water from the 



« Peale, A. C, Mineral springs of the United States: Bull. U. S. Geol. Survey No. 32, 1886, pp. 

 '156, 187, 192, 195, 212, 213. 



&Sliehter, C. S., Theoretical investigation of the motion of ground waters: Nineteenth Ann. Rept. 

 U: S. Geol. Survey, pt. 2, 1899, pp. 297-384. 



