PRINCIPLES CONTROLLING ORE DEPOSITS 



739 



It is now necessary to consider in some detail the manner in 

 which underground water moves. For a long time I have real- 

 ized that if underground water had a difference in head that it 

 might penetrate to a great depth and rise again to the surface ; 



Fig. i. 

 but I did not realize that it was not necessary to assume excep- 

 tional openings for such a circulation. I assumed that where 

 such a circulation took place exceptionally favorable chan- 

 nels were available; but a recent paper by Professor Slichter 1 



1 Theoretical Investigation of the Motion of Groundwaters, by C. S. Slichter, 

 Nineteenth Ann. Rept. U. S. Geol. Surv., 1899, Pt. II, pp. 295-384. 



