ELISHA MITCHELL SCIENTIFIC SOCIETY. 87 



and denudation. They are among the very oldest roeks of this 

 continent, and probably have not been .submerged since the Cam- 

 brian period. We have in them the unmoved remains of the 

 old crystalline rocks, and what is now exposed to our view was 

 formerly overlaid by rocks of the sanieage. When this plateau 

 was elevated, with its border of high mountains on every side, 

 the fissures now filled with the mica veins were opened. The 

 fissures mot naturally followed the line of least resistance. 

 Where this coincided with the line of bedding, a true bedded 

 vein resulted. Where, on the contrary, ; t ran somewhat trans- 

 verse to this line after having followed it for some distance, the 

 vein assumed more of the character of a lode. This seems to 

 me the true explanation of an occurrence sometimes met with, 

 as at the Pizzle mine, where the vein, after coinciding in strike 

 and dip with the inclosing schists, suddenly breaks across the 

 stratification and changes its dip. 



The mica veins in North Carolina are true fissure veins, dif- 

 fering in this respect from the mica veins of New Hampshire, 

 which, according to X. S. Shaler,* "appear to be obscure beds 

 closely following the general run of the apparent bedding that 

 characterizes the granites in this part of the country." 



Hitchcockf ranks the Grafton mica veins in the gneissic series, 

 and savs that valuable deposits are found only within the fibro- 

 lite area (mica schist \Vith fibrolite, one of the supposed divisions 

 of the Montalban Group). This fibrolite area lies in between 

 the two great areas of porphyritie gneiss, very well developed 

 between Rumney and Hebron. 



Of the influence of the walling on the quantity and quality 

 of the mica but little is known. My own investigations on this 

 subject have not yet led to any definite conclusions. Some of 

 the more experienced miners in Mitchell county say that both 

 the quantity and the quality of the mica depend upon the char- 

 acter of the walling and of the vein, but the lack of careful and 



*Tenlh U. S. Census, Vol. XV, p. 833. 



fGeol. of New Hampshire, Vol! I, 1874, p. 26, and Vol. Ill, part V, p. '.hi. 



