394 



THE CRYSTAL FALLS IRON-BEARING DISTRICT. 



amounts in different sections. It incloses quartz, the micas, magnetite, and 

 an older feldspar. These inclosures are usually small; they often lie in par- 

 allel alignment in the same and adjoining microclines, and the lines in which 

 they are disposed sometimes bend, apparently indicating that the oi'iginal 

 rock was minutely puckered. The inclosed quai-tz sometimes incloses 

 smaller flakes of biotite and muscovite, as well as magnetite and rutile 

 needles. The inclosures in the little grains of quartz are frequently con- 

 centrated in the centers, as in the case of some of the quartzes outside the 

 microclines, as described above. The microcline sometimes occurs in a few 

 scattered grains; sometimes with its inclusions it makes up almost the whole 

 rock. In its manner of occurrence, its inclusions, and the way in which 

 these are disposed within it, it is strikingly like the secondary albite of the 

 Hoosac schists of western Massachusetts, described by Prof. J. E. Wolff.^ 



The microclines are distinctly elongated in a direction parallel to the 

 foliation, to which they thus contribute. In a few cases the elongation is 

 parallel to a line, and does not appear in thin sections cut normal to this 

 direction. But in most cases the crystals are flattened parallel to a plane. 

 These forms are those of crystallization; except along the secondary fracture 

 planes the microline is entirely free from breaking or granulation. 



The following is a complete analysis of a representative specimen of 

 the mica-schist: 



Analysis of mica-schist. 



[By J)r. H. S. Stokes, U. S. Geol. Survey.] 



No. 1. Specimen 34822, Lake Superior Division, U. S. Geol. Surv., 1900 N., 1310 W., sec. 35, T. 42 N., 

 R. 29 W., Upper Peninsula of Michigan. 



' Mon. II. S. Geol. Survey, Vol. XXIII, pp. 59-63. 



