114 THE GEOLOGY OP MINNESOTA. 



[Aporhyolyte. Diabase Porphyryte. 



or of the masses, since there are several nuclei, is sometimes seen to be a knot of 

 finely granular or cherty quartz. The elongated fibres are quartzine, being positive. 



N. H. w. 

 No. 13. APORHYOLYTE. 



Duluth. Near midway between Minnesota point and Chester creek, at the lake shore.* Extends fifty- 

 four paces. 



Ref. Annual Report, ix, pages 13, 14. 



Meg. A fine grained brownish rock, in which the only identifiable mineral is a 

 minute lath-shaped plagioclase whose cleavage affords a reflecting surface visible 

 under the loop. The rock breaks with a conchoidal fracture, and outwardly, in the 

 field, it weathers into a laminated or slaty structure which dips east 15. In other 

 places it is a lumpy amygdaloid with epidotic spots and veinings. A little pyrite 

 also is visible in the mass of the rock. 



Mic. The lath-shaped feldspars are usually gray, but some of them are reddened 

 by iron. In reflected light fine metallic particles are visible, both of magnetite and 

 of pyrite. If the rock ever contained pyroxene, it is wholly changed, for the matrix 

 of the feldspars consists of a fine mass of chlor/ti-. in>i//t//'f/fc. </>uiz and apparently of 

 a little calcite. 



One section examined. 



Age. Cabotian. 



Remarks. This seems to be one of a series of rocks, of which several have 

 already been described, viz.: the porphyrytes and diabase porphyrytes, Nos. 7BC, 8, 

 9, 10. No. 13A is also similar. They may all be considered Cabotian lavas that fol- 

 lowed soon after the Beaver Bay diabase. N. H. w. 



No. 13A. DIABASE POHPHYRYTE (?) 



Duluth. Overlies No. 13, being apparently a layer of No. 13. 

 Ref. Annual Report, ix, pages 13, 14. 



Meg. Slightly amygdaloidal and porphyritic, having a brown color and close 

 texture. Except in its disseminated red feldspars, which appear more on one side 

 of the specimen than on the other, this rock is like No. 13. 



Mic. The feldspars are fine and tubular, striated, much decayed. The inter- 

 vening groundmass consists of >/n/ni,:, clcit<\ /irtiitiiit'. nxit/ttHitc, and an isotropic 

 substance whose nature is unknown. E/iiilotc is not abundant, but occurs sparingly. 



One section examined. 



Age. Cabotian. 



* The lake shore east from Minnesota point was formerly rock bound. It was examined carefully, and these specimens 

 were collected when tin- alternations could easily be note 1. Since then buildings have been erected, which, with street grading, 

 have effectually hid all these outcrops. It can only be said that from No. 7D up to No . 3tt. from the mouth of Kinichigaquag (now 

 Chester) creek, the descriptions apply to rocks occurring between Minnesota point and that creek, all situated within the limits 

 of Duluth. There will probably never be an opportunity to verify the succession. In general these numbers represent the 

 "porphyry-like melaphyr" mentioned by Mr. Kloos. 



