114 NEW YORK STATE MUSEUM 



activity of some mctamorphic agency sufficient to change tlie orig- 

 inal hematite or pyrite to magnetite. Its appHcation could hardly 

 be extended to the other occurrences, which are inclosed by a single 

 rock mass, a condition that is quite general in the magnetites of the 

 Archean. 



The visit to Kiruna and Gellivare was interesting furthermore 

 for the insight it afforded in regard to the changes wrought by 

 regional metamorphism. There can be no doubt of the fundamental 

 similarity between the two localities as has been emphasized by 

 Lundbohm.^ At Kiruna, however, the ores and wall rocks have 

 remained undisturbed since their formation ; while at Gellivare the 

 rocks have been so compressed and crushed that they have lost 

 largely their original structures, and the magnetites with their in- 

 cluded minerals have assumed a coarsely crystallized phase. To 

 extend the comparison even further it may be said that our Adiron- 

 dack magnetites illustrate the extreme effects of metamorphism, a 

 more advanced stage than is evidenced by the conditions at Gelli- 

 vare. Here, the rocks only seldom show anything in the way of 

 structures that can be taken as original, they are interfolded in the 

 most intricate manner, and the ore bodies are of the most varied 

 and complex shape. Yet in these features they appear not more 

 removed from the Gellivare occurrences than the latter are from the 

 Kiruna deposits. 



The excursion through central Sweden, which followed the close 

 of the sessions in Stockholm, afforded opportunity for a brief visit 

 to the Dannemora, Norberg, Flogberget, Grangesberg and Langban 

 iron mines. The writer did not continue with the party to Persberg 

 and Taberg, but instead made a trip to the mines at Striberg and 

 vicinity which were off the route of the regular excursion. 



The magnetites of this district present a great variety of char- 

 acters and modes of occurrence, and it is impracticable in this place 

 to do more than call attention to some features that have a com- 

 parative interest. Their investigation is attended with extraordinary 

 difficulties, as will be appreciated by anyone familiar with the occur- 

 rences or with the painstaking work that has been done by the 

 Swedish geologists in this field. * 



The Precambric complex that contains the magnetites is an in- 

 tricately involved assemblage of gneissoid and massive igneous 



1 Sketch of the Geology of the Kiruna District. Guide to the Excursions 

 of the International Geological Congress. Stockholm, 1910. 



