1072 A TREATISE ON METAMORPHISM. 



greater depths; for, as full)' explained (pp. 1030-1036), magma, carrying 

 various metals with it, does rise from unknown depths into the zone of 

 fracture upon an enormous scale, and there yields its metallic contents to 

 circulating waters. 



My third main conclusion is that the metals for ores deposited by aqueous 

 solutions are derived from rocks within the zone of fracture. 



III. WORK OF AQUEOUS SOLUTIONS IN SEGREGATING ORES. 



The work of aqueous solutions in segregating ores is most complex. 

 The ores produced by aqueous solutions may be divided into three sub- 

 classes — (1) ores precipitated from aqueous solutions by ascending waters, 

 (2) ores precipitated from aqueous solutions by ascending and descending 

 waters combined, and (3) ores produced by precipitation from descending 

 waters. As the processes of segregation of each of these classes of ores are 

 distinctive, each class will be considered in turn. In order to produce any 

 of the ores of all these subclasses three stages of work need to be consid- 

 ered — the solution of the valuable metals, the transportation of them to the 

 places where they are deposited, and their precipitation. 



SUBCLASS 1. ORES PRECIPITATED FROM ASCENDING AQUEOUS SOLUTIONS. 



There have been endless discussions as to whether ore deposits are pro- 

 duced by descending', lateral-secreting, or ascending waters. It is believed 

 to be a corollary from what has gone before that the first concentration of 

 many ore deposits is the result of descending, lateral-moving, and ascending 

 waters. I say first concentration, for it will subsequently appear that many, 

 if not the majority, of the workable ore deposits precipitated from aqueous 

 solutions have undergone a second concentration. If the waters which 

 deposit ores are mainly meteoric, such waters at the outset are descending. 

 In most cases before they again issue at the surface they must ascend. 

 During the journey they have a lateral movement. 



Thus, the larger, more complete idea of the genesis of aqueous ore 

 deposits comprises all of the old ideas, and shows that instead of being 

 contradictory, as supposed by many, they are mutually supporting. Com- 

 bined, they furnish a much more satisfactory theory than any one of them 

 alone. How true these statements are will appear more clearly later. 



