emmons.]    COPPER  IN  RED  BEDS  OF  COLORADO  PLATEAU.        231 
at  the  same  horizon.  My  own  observations  were  made  at  a  still  lower 
horizon,  however — namely,  the  Red  Wall  or  lower  Carboniferous 
limestone — in  the  so-called  Grand  Canyon  mine,  that  is  being  worked 
by  a  shaft  200  feet  deep  and  by  a  <*rosscut  tunnel  that  connects  with 
ore.  This  mine  is  reached  by  the  Grand  view  trail,  which  descends 
the  canyon  Avails  about  12  miles  east  of  "  Bright  Angel,"  the  point 
reached  by  the  railroad,  and  about  a  mile  west  of  the  Old  Hance 
trail,  by  which  travelers  descended  into  Congress  Canyon  when  the 
approach  was  b/y  coach  or  wagon  from  Flagstaff.  The  mine  is  situ- 
ated at  the  upper  edge  of  the  platform  formed  by  the  Red  Wall  lime- 
stone and  2,500  feet  below  the  rim  of  the  canyon  wall.  It  is  opened 
by  a  shaft  200  feet  deep  and  b/y  a  crosscut  tunnel  that  connects  with 
the  bottom  of  the  shaft.  A  second  tunnel  was  started  200  feet  lower 
down  and  has  been  driven  a  distance  of  500  feet,  but  has  not  yet 
reached  the  ore. 
The  ore  is  mostly  blue  and  green  carbonates  with  chrysocolla,  but 
chalcocite  has  been  found  in  the  center  of  the  larger  masses,  one  of 
which,  to  judge  by  the  opening  left,  must  have  been  8  or  10  feet  in 
diameter.  There  are  no  gangue  minerals,  and  of  other  metallic 
minerals  none  were  seen  except  a  very  little  finely  divided  pyrite. 
One  small  specimen  of  chalcopyrite  was  seen,  which  was  said  to 
have  come  from  the  mine.  The  limestone  country  rock  in  the  neigh- 
borhood of  the  deposit  has  been  bleached  and  partially  marbleized. 
This  limestone  is  very  much  decomposed  along  a  rather  ill-defined 
shear  zone,  which  trends  about  N.  65°  E.  Much  of  the  decomposed 
portion  is  a  wdiite  clay-like  material,  which  the  miners  thought  to 
be  porphyry.  I  could,  however,  find  nothing  in  or  near  the  mine 
which  I  could  consider  as  surely  of  eruptive  origin. 
The  ore  is  very  irregularly  distributed  through  the  shear-zone 
material,  generally  in  the  form  of  strings  and  flakes  of  carbonate 
on  cracks  and  thin  seams.  It  sometimes  occurs  also  in  the  limestone 
at  considerable  distances  from  the  shear  zone.  At  times  it  is  con- 
centrated into  bunches,  which  often  show  a  kernel  of  sulphide,  or 
again  it  forms  the  lining  of  small  caves  or  vugs,  when  it  may  assume 
very  beautiful  crystalline  forms. 
The  deposit  is  situated  in  the  line  of  one  of  the  north-south  mono- 
clinal  folds  which  are  characteristic  of  this  region  and  which  often 
pass  into  faults,  but  the  strike  of  the  shear  zone  is,  as  nearly  as  could  be 
determined,  at  right  angles  to  that  of  the  monocline.  A  winze  had 
gone  down  40  feet  below  the  level  of  the  upper  tunnel  and  was 
still  in  ore,  but  the  lower  tunnel  had  not  reached  ore,  though,  as 
well  as  could  be  determined  without  instrumental  measurement,  it 
should  already  have  cut  the  shear  zone. 
The  nearest  eruptive  rock  is  an  80-foot  bed  of  basalt,  a  mile  or 
two  distant,  near  the  bottom  of  the  canyon,  which  runs  a  few  feet 
