NOMENCLATURE OF KEWEENAW AN IGNEOUS ROCKS 773 



The olivine diabase belongs to the same class as the Birch Lake 

 olivine gabbros, the Lighthouse Point diabase, and several others, 

 that is, to the auvergnose type, which seems to be the dominant 

 type of the Keweenawan, although the hessose type, which differs 

 only in having a greater proportion of salic minerals, is also quite 

 abundant. But the "ashbed" diabase classifies as a camptonose, 

 very near a kilauose. It is therefore related to Irving's melaphyre 

 of Bed 87 of the Eagle River section, and to the more basic phases 

 of the orthoclase gabbro of Duluth. 



It is to be expected that additional analyses of the Keweenawan 

 volcanic rocks would disclose still other types, especially such as 

 would parallel the known plutonic types. The parallelism in com- 

 position already established is quite remarkable, considering the 

 relatively small number of analyses available. Thus, it appears that 

 Lane's porphyrite (No. IV) and ophite (No. VII), as well as Sweet's 

 Douglas County diabase and Wadsworth's diabase granophyrite 

 from the Cleveland mine, are the chemical equivalents among the 

 volcanic and dike rocks of Bayley's olivine gabbro from Pigeon Point 

 and from T. 61 N. R. 12 W., and of A. N. Winchell's olivine gabbro 

 and diabase from Birch Lake among the plutonic rocks. Again, 

 Pumpelly's melaphyre from the middle of Bed 87 and Lane's por- 

 phyrite (Nos. V and VII) from Isle Royale correspond chemically 

 with the coarse hornblende gabbro and orthoclase gabbro from 

 Duluth. Finally, the same chemical type, viz., auvergnose, includes 

 plutonic rocks such as Bayley's gabbro and olivine gabbro from 

 Birch Lake, N. H. Winchell's gabbro from Bashitanaquab Lake, 

 and A. N. Winchell's troctolite, together with volcanic or dike rocks 



