NEW YORK ACADEMY OF SCIENCES 641 



be concentrated in order that they may be objects of mining. 

 The next step is to establish first the agent or solvent which 

 can effect the collection of the sparsely distributed metals, 

 and second the places where the precipitation of them takes 

 place. We may then inquire more particularly into the source 

 of the agent and the methods of its operation. In order to 

 do this in the time at command I must remorselessly focus 

 attention on the larger and essential features, resolutely avoiding 

 every side issue or minor point, however inviting. 



The one solvent which is sufficiently abundant is water, 

 and practically all observers are agreed that for the vast majority 

 of ore deposits it has been the vehicle of concentration. Of 

 course it need not operate alone. On the contrary easily 

 dissolved and ever-present materials, like alkalies, may and 

 undoubtedly do increase its efficiency. It does not operate 

 necessarily as cold water. On the contrary, we all know that the 

 earth grows hotter as we go down, so that descending waters, 

 could not go far without feeling this influence. Volcanoes, 

 too, indicate to us that there are localities where heat is developed 

 in enormous amounts and not far below the surface. There 

 is, therefore, no lack of heat, and we need only be familiar with 

 the Western country to know that there is no lack of hot springs 

 when we take a comprehensive view. As solvents, hot waters 

 are so incomparably superior to cold waters that they appeal 

 to us strongly. We may, therefore, take it as well established 

 that water is the vehicle. The chemical compounds which 

 constitute the ores naturally differ widely in solubility, and no 

 sweeping statements can be made regarding them. Iron, 

 for example, yields very soluble salts and is widely, one might 

 almost say universally, distributed in ordinary waters. Its 

 ores are compounds of the metal with oxygen and in this respect 

 it differs from nearly all others, which are mostly combined 

 with sulphur. Although almost all of them have oxidized 

 compounds, the latter are on the whole very subordinate con- 

 tributors to our furnaces. 



Iron is everywhere present in the rocks, and when exposed 

 to the natural reagents it is one of their most vulnerable elements. 

 It, therefore, presents few difficulties in the way of solution 



