410         CONTRIBUTIONS   TO    ECONOMIC    GEOLOGY,  1906,  PART    I. 
for  only  about  100  feet.  The  pegmatite  is  fairly  regular  in 
thickness  and  would  probably  average  8  feel  through  a  large  part 
of  the  mine.  In  certain  places  where  the  full  width  of  the  "vein" 
had  been  removed  rooms  12  to  15  feet  high  were  left.  The  greater 
part  of  the  pegmatite  has  a  coarse  granitic  texture.  A  peculiar 
graphic-granite  texture  has  been  observed,  in  smaller  portions  of  the 
pegmatite,  caused  by  a  parallel  orientation  of  biotite  plates  in  a  feld- 
spar-quartz matrix.  A  thin  section  cut  from  a  piece  of  this  nature 
showed,  under  the  microscope,  a  semimicrographic  arrangement  of 
quartz  in  feldspar  crystals.  The  feldspar  is  largely  albite.  A  large 
amount  of  biotite,  probably  amounting  to  one-fourth  or  one-third 
of  all  the  mica  contained  in  the  "vein,"  is  found  with  the  clear  mica. 
In  places  the  two  form  intergrowths  with  one  another.  Apatite, 
hornblende,  and  garnet  are  found  as  accessory  minerals.  The  mica 
is  of  clear,  lighl  "rum"  color  and  excellent  quality.  The  mine  has 
been  worked  for  many  years  and  has  been  a  good  producer.  It  is 
often  closed  during  part  of  the  winter,  as  it  is  found  difficult  to  keep 
up  sufficienl  steam  to  run  the  air  compressor  at  such  an  elevation 
during  the  cold  weather. 
CATTAIL    BRANCH    MINE. 
The  Cattail  Branch  mine  is  near  the  head  of  Cattail  Branch,  in 
Yancey  County,  about  5,500  feet  above  sea  level  and  nearly  a  mile" 
southwest  of  Celo  Mountain,  the  north  end  of  the  Black  Mountains. 
It  was  discovered  about  2  years  ago  by  Silvers  &  Son  and  B.  Holland, 
all  ^\'  Yancey  County.  The  developments  consist  of  open  cuts  at 
three  different  points  on  the  outcrop.  The  country  rock  is  biotite 
gneiss.  Near  the  pegmatite  it  is  much  Hexed  and  folded,  striking 
northeastward  with  uearly  vertical  folds.  The  pegmatite  is  in  the 
form  of  an  inclined  trough  with  a  horseshoe  or  U-shaped  cross  sec- 
tion. The  hot  torn  of  the  trough  pitches  about  55°  SAY.  and  cuts 
directly  across  the  country  rock.  The  sides  are  nearly  vertical  and, 
at  a  linlc  distance  from  the  bottom  of  the  trough,  conform  in  a  gen- 
eral way  with  the  strike  of  the  country  rock.  The  thickness  of  the 
pegmatite  varies  from  3  feel  in  the  curve  of  the  horseshoe  to  20  feet 
or  more  some  distance  out  from  the  curve.  This  includes  horses  or 
tongues  of  wall  rock  around  which  the  pegmatite  has  forked.  About 
30  feet  southwest  of  the  curve  the  northwest  arm  is  nearly  25  feet 
thick,  the  greatest  thickness  exposed.  The  "vein"  must  have 
bulged  out  abruptly  to  attain  such  a  thickness  at  this  point.  It  con- 
tains mica-gneiss  bands  or  horses,  from  a  few  inches  up  to  a  maximum 
in  one  place  of  several  feet  in  thickness,  and  oriented  parallel  to  the 
walls.  The  southeast  arm  shows  a  similar  bulging,  being  about  12 
feet  thick  at  a  distance  of  25  feet  from  the  curve. 
