PRINCIPLES CONTROLLING ORE DEPOSITS 75 I 



have been derived to fill the cracks and crevices of the entire 

 belt of cementation below, although this belt may be thousands 

 of meters thick. This process of filling cracks and crevices by 

 deposition is the general law for the great belt qI cementation 

 below the level of groundwater, just as certainly as solution is the 

 general law for the belt of weathering above the level of ground- 

 water. These are the dominant processes. However, I by no 

 means assert that deposition does not occur in the belt of 

 weathering, and that solution does not occur in the belt of 

 cementation. Indeed, the solution of material in various places, 

 in both the belts of weathering and cementation, and the deposi- 

 tion of this same material or a part of it in the same belts at 

 other places are very important processes. 



We therefore conclude that the solution of material in the 

 belt of weathering and the deposition of material in the belt of 

 cementation, and the solution and deposition of material within 

 the same belts, fills the openings in the rocks below the level of 

 groundwater. These processes are gradually changing the soft 

 sandstones, such as exist below the surface limestone of Chicago, 

 into quartzite. By the same processes fractures — small and 

 great, from minute joints to great fissures — are filled by deposi- 

 tion of material from underground waters. The formation of ore 

 deposits is largely an incident of this process. The volume of 

 material transported from the belt of weathering and deposited 

 below in the openings of the belt of cementation, and trans- 

 ferred from place to place within these belts, is many million 

 times greater than the ore deposits. The development of ores is 

 merely an exceptional case of a widespread and most important 

 geological process, the deposition of ores involving only a con- 

 sideration of the particular materials which are of value to man. 

 This evening I propose very briefly to discuss the source of 

 such materials : how they are carried ; why and where they are 

 deposited. The particular case is under the general laws which 

 control the general process of solution and deposition. 



There are a great many chemical laws which affect the 

 process of ore deposition, and a few of them I am obliged to 



