510 U. s. GRANT— CONTACT Nf ETAMORPHISM OF HASH' IGNEOUS ROCK 



in the granulitic gabbros. Moreover, in the metamorphosed greenstones 

 there is usually much hornblende and sometimes a little quartz, and it 

 is only in close proximity to the gabbro that augite and hypersthene 

 are found in any considerable amounts. Olivine has not been noted, 

 and quite frequently the hornblende and hypersthene are in poikilitic 

 plates. 



Summary 



In conclusion, it may be stated that the great mass of gabbro at the 

 base of the Keweenawan in Minnesota has features which indicate its 

 intrusive rather than its extrusive nature; that one of the most impor- 

 tant of these features is the marked contact zone along the lower or 

 northern side of this mass ; that in this zone a complete recry stall ization 

 of the strata has been effected, at times for a distance of a few hundred 

 feet from the igneous rock, with less pronounced effects extending for a 

 quarter of a mile or more ; that the rocks resulting from the contact 

 metamorphism of the iron-bearing member of the Animikie are pecu- 

 liarly rich in minerals of the basic rocks — that is, in augite, h} T persthene, 

 and olivine; that the materials for these minerals were present in the 

 (juartz-magnetite-amphibole slates of the Animikie, and consequently 

 that it is not necessary to consider these minerals as derived from the 

 gabbro ; and that the contact effects on some altered basic igneous rocks 

 have been to reproduce the original mineral characters of these rocks and 

 to produce textures partially similar to true igneous rocks. 



