PRINCIPLES CONTROLLING ORE DEPOSITS 737 



into the sandstone below you know that great quantities of 

 water issue. The water falls upon the ground far to the north- 

 west in central Wisconsin, where the sandstone reaches the 

 surface. It follows this pervious formation below impervious 

 strata, and when the impervious strata are punctured at Chicago 

 rises to the surface through the opening. So it is with artesian 

 wells everywhere. I repeat, The waters which we know to be vig- 

 orously circulating are of meteoric origin, a?id these are the waters 

 which have deposited the ores. 



We are now ready to pass to the fourth of my premises, viz., 

 The movemerit of underground water is mainly due to gravitative 

 stress. This is perhaps so plain to you as engineers that it will 

 hardly need proving; but certainly many men who have written 

 about ore deposits have given other explanations. Why does 

 the water rise in the artesian wells in Chicago ? Simply because 

 the level of underground water at the northwest where the sand- 

 stone is fed is at a higher elevation. The difference in eleva- 

 tion is only a few hundred feet ; and yet the difference in the 

 weight of the columns, or the force of gravity, is sufficient to 

 drive the water underground through the sandstone for a hun- 

 dred or more miles to Chicago and make it rise considerably 

 above the level of Lake Michigan. If the deformation had been 

 such that the porous formation had somewhere been depressed 

 nearly to the bottom of the zone of fracture, and the openings 

 did not thereby become smaller, this in no way would have les- 

 sened the speed of circulation. It is therefore clear from our 

 knowledge of artesian wells that a very moderate head is entirely 

 adequate to account for an underground lateral circulation of 

 great length and for a vertical circulation of great depth — 

 entirely adequate to account for it. If this be true, why should 

 we appeal to subterranean heat or to the unknown mysterious 

 forces at the depths as a main cause for underground circula- 

 tion ? 



I do not deny that in some cases water is squeezed out of 

 the rocks by orogenic movements, nor do I deny that heat pro- 

 duces an effect in underground circulation. We may suppose, 



