IIIKOHIKS OK OHK l)ISI'( )SITI()N 1 1 ISTOHICALLV CONSIDERED. 835 



yet Ihvii studied in America. Tlic tcrni " contiU'l (l('i)()sii,s," wliicli 

 had hitherto hccii loosely appiiiMl to ail deposits, without rej^ard to 

 ori<rin. which happened to lie near the contact of any two l)odi(s of 

 rock, was restricted l)V Ids defiintion to those occiin-in*; near the con- 

 tact of iiiiH'ous intrnsi\('s witli calcai'eous beds. They are chai-acter- 

 ized by iri-e<>idarity of form, the association of iron oxide and 

 suli)hides of the metals ^vith various lime silicates, <renerally called 

 '• contact " minerals because they are found to l>e the result of contact 

 metamor|)hism. 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 

 amon<i- European «:;e()logists since the middle of the century, but the 

 metallic deposits coiniected with them being generally of subordinate 

 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 numl)er of economically impoi'tant deposits, 

 especially of copper, which wovdd 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 opposition to the view so emphatically voiced 

 l\v Van Hise. that the majority of our ore deposits have been formed 

 by precipitation from circulating w^aters of original meteoric origin. 

 In this Kemp maintains that ground-w ater circulation is not sufficient 

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

 must have furnished not only their metallic contents, but a large, if 

 not predominating, proportion of the w^aters which brought them into 

 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 AY. H. AVeed 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 greatly enlarging the scope of his pneunuitolytic class. The 

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

 on ore deposits, especially in articles Avhere 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 wdiich he is 

 describing. 



