86 JOURNAL OF THE 



especially if fragments of the walling were included in the vein. 

 That such fragments are thus included in mica veins will appear 

 from the discussion in Article II of this series. 



The inclosing rocks, whether micaceous schists, slaty gneisses 

 or gneissoid micaceous schists, have a general strike toward the 

 north-east, and a general dip toward the south-east, at angles vary- 

 ing from 40 to 90 degrees. The mica veins share these charac- 

 teristics more or less completely, and are hence bedded veins. 



So far as known the walling is the same on both sides of the 

 vein. Contact deposits do not occur in this region as they do at 

 the junction of sandstones and schists near Mts. Lincoln and 

 Bross, in Colorado.* When the Silvers or Sink Hole mine was 

 first opened in 1868-'69, the upper part of the vein was a decom- 

 posed feldspar; at 20 feet depth this passed into granite, and at 

 60 feet the vein narrowed so that work was suspended for a 

 while. f The vein was afterwards found to widen again, while 

 still in granite. 



Good crystals of mica, sometimes of several inches in dimen- 

 sion, have been observed in Prozoic granites of the Sweetwater 

 Districts, Idaho,! as also iu the granite of the Black Hills.§ 



At this latter locality they form about 5 per cent, of the granite, 

 this proportion, as will hereafter appear, being somewhat below 

 the average yield of "cut" mica from North Carolina "block' 

 mica. It is interesting to note, also, that the crystals of mica in 

 the granite occur in bunches or segregations, a phenomenon 

 likewise characteristic of some Mitchell countv mines. 



The inclosing rocks in North Carolina have suffered many and 

 great dislocations; they are bent, curved and twisted in a variety 

 of ways without, however, giving rise to faults in the vein. The 

 irregularities of the veins, therefore are those of form, size, 

 strike and dip, rather than of position. It must not be forgot- 

 ten that the rocks of this district have suffered enormous erosion 



*U. S. Geol. and Geogr. Survey of Colorado, 1873, p. 269. 

 f D. A. Bowman, Mitchell county, priv. com., Nov. 5, 1887. 

 JU. S. Geol. and Survey of Idaho and Wyoming, 1877, p. 158. 

 §U. S. Geol. Survey, Black Hills, 1880, p. 70. 



