ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 169 



situated above ; we may speak of it as "infiltration from above," 

 and if it deposits anything in the fissure, it can only be material 

 derived from the superficial strata, such as could be dissolved 

 without any particular elevation of temperature or pressure. 

 In the same way waters coming in at deeper points and having 

 higher temperatures due to their greater depths of origin may 

 be expected to dissolve, and afterwards to deposit in the fissure 

 some additional material, and such deposits may fairly be called 

 ''lateral secretions." Similarly the waters reaching the fissure 

 at still greater depths, having traversed greatly heated rocks, 

 and having had greater opportunities of meeting with active re- 

 agents will be still better solvents, and may therefore be expected 

 to deposit in the fissure, as they rise up through it, still other 

 and different constituents, affording thus examples of deposit 

 by "ascension." This part of the subject will be more fully 

 dealt with in Sec. 1 0. 



The solvent powers of water, especially when heated and 

 under pressure, are so great and general that it has been called 

 with almost literal exactness, the universal solvent. And the 

 springs however charged rarely deposit the whole of their 

 dissolved contents on the sides of their channels, consequently 

 natural springs afford on analysis a great variety of chemical 

 substances. It is indeed remarkable how many of the substances 

 known to us as components of the air or of the solid earth are 

 found to exist in greater or lesser proportions in natural thermal 

 waters. Thanks to the labours of Forchhammer, Bischoff, 

 Daubree, and a host of other writers, the fifth axiom of my 

 introduction* may be regarded as fully established. 



Daubreef gives the following list of substances that have 

 been found by analysis in such waters. 



Gases. Oxygen, hydrogen, nitrogen, carbonic acid, car- 

 buretted hydrogen, sulphuretted hydrogen. 



Metalloids. Sulphur, selenium, phosphorus, carbon. 



* "All rocks and mineral substances are more or less soluble in pure water, 

 and still more so in water containing carbonic acid, or other active chemical 

 substances in solution ; such waters in fact as are found to circulate in sub- 

 terranean channels and fissures." 



t Les eaux souterraines. 



