GABBEO AND NOEITE INTRUSIVES. 



Analyses of norites. 



245 



SBC. 29, T. 42 N., R. 31 w., 1,200 N., 200 w. 



On the east bank of the Michigamme River at 1,200 paces N., 200 W., 

 sec. 29, T. 42 N., R. 31 W., there is an outcrop which shows even better 

 than the occurrence just described the variation in mineralogical character 

 and the relative ages of these varieties. At this place there is a knob com- 

 posed of hornblende-gabbro essentially like the general type described as 

 typical for this district. This knob is cut by a rock which is coarser in 

 grain and a trifle darker than the variety which it intrudes. Examined 

 under the microscope, it is seen to differ from the normal phase also in min- 

 eralogical composition, and resembles rather closely in this respect the 

 porphyritic variety described on p 240. Like that, the hornblende is reddish- 

 brown, containing a large number of inclusions and grading over into the 

 green hornblende. This hornblende includes rounded grains of a white to 

 pinkish monoclinic pyroxene in suificient quantity to be characteristic. The 

 pyroxene is never automorphic, as one would perhaps expect to find it, 

 though it was evidently one of the first minerals to crystallize. Contained in 

 the pyroxene individuals are rounded areas of yellowish-green serpentine. 

 These areas are sharply outlined from the pyroxene and do not ajipear to be 

 the result of its alteration; consequently the conclusion is reached that the 



