THE VERIFICATION PERIOD 27 



In his article " On metasomatic processes in fissure veins," Lindgren 

 placed this theory for the first time on a scientific basis of chemical and 

 microscopical study, and by a classification of veins according to the 

 predominant metasomatic mineral or process involved, he made its ap- 

 plication much clearer to the student and observer. In his closing 

 remarks he suggested that of late sufficient attention had not been given 

 to the French theory of emanations from eruptive magmas, and that in 

 the case of metals with low critical temperature they may have first 

 been carried up under pneumatolytic conditions and with the aid of 

 mineralizers while still above the critical temperature, until they reached 

 the zone of circulating atmospheric waters. 



His paper " On contact deposits " (1901), following out this suggestion, 

 served a useful genetic purpose by calling attention to and clearly defining 

 a group of deposits for which a pneumatolytic origin would readily be 

 admitted, but of which no important examples had yet been studied in 

 America. The term " contact deposits," which had hitherto been loosely 

 applied to all deposits, withoutregard to origin, which happened to lie near 

 the contact of any two bodies of rock, was restricted by his definition to 

 those occurring near the contact of igneous intrusives with calcareous beds. 

 They are characterized by irregularity of form, the association of iron 

 oxide and sulphides of the metals with various lime silicates, generally 

 called " contact " minerals because they are found to be the result of con- 

 tact 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 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 empha- 

 sized by the discovery on this continent,soon after the publication of Lind- 

 gren's paper, of a number of economically important deposits, especially 

 of copper, which would come within his definition of contact deposits. 



From a more theoretical point of view the contemporaneous paper of 

 Kemp, " The role of igneous rocks in the formation of veins," presented 

 a more decided opposition to the view so emphatically voiced by Van 

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

 tation from circulating waters of original meteoric origin. In this Kemp 

 maintains that groundwater 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, pro- 

 portion of the waters which brought them into their present position. 



The controversy which had thus arisen as to the relative importance 



