THEORIES OF ORE DISPOSITION HISTORICALLY CONSIDERED. 335 



yet been studied in America. The term " contact deposits." which 

 liad hitherto l)een hu)seTy apj^lied to all deposits, without regard to 

 origin, which happen(\dto tie near the contact of any two l)odies of 

 rock, Avas restricted hy ids definition to those occurring near the con- 

 tact of igneous intrusives with calcareous l>eds. They are character- 

 ized by irregularity of form, the association of iron oxide and 

 sulphides of the metals with various lime silicates, generally called 

 " contact " nnnerals because they are found to be the residt of contact 

 metamorphism. Typical developments of these contact minerals 

 near Christiania in Norway, in the Banat in Servia, in Tyrol, Italy, 

 and elsewhere had been the subject of repeated study and discussion 

 among European geologists since the middle of the century, but the 

 metallic deposits connected with them being generally of sulwrdinate 

 economic importance had, up to the time of Vogt, not been considered 

 worthy of a distinct place in the classification of ore deposits. 



The importance of pneumatolysis in forming ore deposits was em- 

 phasized by the discovery on this continent, soon after the publication 

 of Lindgren's paper, of a number of economically important deposits, 

 especially of copper, which would come within his definition of con- 

 tact deposits. 



From a more theoretical point of view the contemporaneous paper 

 of Kemp, " The role of igneous rocks in the formation of veins." pre- 

 sented a more decided op]:)osition to the view so emphatically voiced 

 by Van Hise, that the majority of our ore deposits have been formed 

 by precipitation from circulating waters of original meteoric origin. 

 In this Kemp maintains that ground-water circulation is not sufficient 

 to account for the nuijority of ore deposits, but that igneous rocks 

 must have furnished not only their metallic contents. l)ut a large, if 

 not predominating, proportion of the waters which brought them ]nto 

 their present position. 



The controversy which had thus arisen as to the relative importance 

 in the formation of ore deposits of waters of meteoric or of igneous 

 origin has more recently received a further impulse in the discussions 

 provoked by the presentation of proposed genetic classifications of ore 

 deposits by "W. H. AA^eed and J. E. Spurr. These geologists took an 

 even more advanced position than Vogt in regard to the direct influ- 

 ence of igneous agencies in the formation of ore deposits, adding 

 siliceous segregations to his class of magmatic differentiation products 

 and very greath^ enlarging the scope of his pneumatolytic class. The 

 influence of these new vieAvs is already seen in the current literature 

 on ore deposits, especially in articles where the author, though not in 

 possession of full data, still feels it incumbent upon him to present 

 some tentative hypothesis of origin for the deposits which he is 

 describing. 



