1066 A TREATISE ON METAMORPHISM. 



ground water. But the water of meteoric origin is held to be dominant. It 

 has already been noted that the great iron-ore deposits have been concen- 

 trated by waters of meteoric origin. It is further believed that the waters 

 from which were deposited many other ores, the association of which show 

 they were precipitated from aqueous solutions, are also dominantly of 

 meteoric origin. It has been shown already that in order to produce 

 aqueous ore deposits the amount of water required was probably many 

 thousands of times the volume of the minerals deposited. If this be so, 

 even if all the water exuded from magmas at their time of crystallization 

 could be supposed to be converged into the trunk channels holding the 

 ore deposits, this would be but a fraction of that required for the segregation 

 of the ores. 



It is impossible to make an exact quantitative estimate of the relative 

 proportions of the waters of meteoric origin and igneous origin concerned in 

 the production of aqueous deposits. But I have no doubt whatever that 

 water of meteoric origin forms more than 95 per cent of such waters, and I 

 think it probable that it constitutes more than 99 per cent, if all ore deposits 

 produced by underground water are taken into account. Mistaken concep- 

 tions upon this point frequently have been due to the fact that authors in 

 considering this matter often take into account only ores of a part of the 

 metals, such as those of gold or silver, whereas a general statement with 

 reference to the proportion of water of meteoric origin should take into 

 consideration deposits of iron ore and of the other base metals. Even in 

 the case of ore deposits closely associated with igneous rocks, it is believed 

 that the water is dominantly of meteoric origin. For instance, at the 

 present time, ore deposits are known to be in the course of formation at 

 Steamboat Springs, Sulphur Bank, the Comstock lode and Boulder Hot 

 Springs, Mont., described by Weed." The same is probably also true of 

 the numerous hot springs of Yellowstone Park. The quantity of water 

 which issues from these hot springs is enormous. These springs, in vol- 

 ume of water and in their relation to the topography and precipitation, 

 are in all respects like the vastly more numerous and more important 

 springs which have ordinary temperatures. The study of underground 

 circulation with reference to artesian waters has shown beyond question 

 that the waters discharged from the great majority of springs is of meteoric 



a Twenty-first Ann. Rept U. S. Geol. Survey, pt. 2, 1900, p. 227-255. 



