60  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.        [bull.  2fi0. 
the  greatest  economic  importance,  and  is  the  most  important  silver 
producer  in  the  district  as  well  as  the  most  productive  of  the  fissure 
veins.  It  possesses  so  many  features  that  can  not  readily  be  presented 
in  a  general  discussion,  and  is  in  some  respects  so  peculiar  that  an 
account  of  the  silver  veins  would  hardly  be  complete  without  a 
detailed  description  of  this  mine.  The  mine  has  been  described  in 
considerable  detail  by  Dr.  F.  L.  Ransome,  of  the  United  States  Geo- 
logical Survey,  in  a  paper  entitled  "A  clastic  dike  and  its  associated 
ore  deposit  near  Ouray,  Colo/' "  The  observations  upon  which  the 
accompanying  description  is  based  were  the  result  of  an  extended 
personal  examination  by  the  writer,  covering  a  considerable  period 
of  time,  and  were  independent  of  Doctor  Ransome's  work. 
The  Bachelor  mine. — The  Bachelor  vein  has  been  opened  in  three 
places:   (1)   At  the   Bachelor   tunnel   in   Dexter   Creek,    (2)   at   the 
Wedge  shaft  on  Gold  Hill,  (3)  at  the  Neodesha  mine,  at  the  base  of  | 
the  cliff  in  Uncompahgre  Canyon.     The  main  openings  are  those  in  i 
Dexter  Creek.     A  tunnel  here  driven  southward  into  the  hill  inter- 
sects the  vein  at  a  distance  of  720  feet.     The  country  rocks  through  i 
which   the  vein   passes   are  sediments   of  the  Mancos   and   Dakota 
Cretaceous  and  the  McElmo  series  of  the  Jurassic.     (See  columnar 
section,   fig.    1,   p.    56.)      Beginning   with   the   highest   level   of   the 
mine,  they  consist  of  (1)  a  series  of  very  fine  black  shales,  in  places 
highly  bituminous  and  often  containing  thin  beds  of  blackish  sand- 
stone;  (2)   layers  of  quartzite  varying  from  2  to  30  feet  in  thick-  • 
ness,   separated    from   one   another   by    varying    intervals   of   black 
and  clay  shales.     The  overlying  black  shales  belong  to  the  Mancos  I 
group  and  the  upper  quartzites  and  the  black  shale  layers  in  them  | 
belong  to  the  Dakota  group.     The  clay  shales  and  other  interbedded 
rocks  belong  to  the  McElmo  series.     The  latter  shales  are  usually  i 
greenish  in  color,  and  at  times  nearly  white,  but  are  so  much  altered 
by  the  action  of  near-by  eruptive  rocks  that  they  break  with  con-  j 
choidal  fracture  into  large,  angular  masses.     Weathering  will  some- 
times  disintegrate  them  so  that  they  do  not  show  much  difference 
from  ordinary  greenish  shale  unaffected  by  metamorphism,  but  in  j 
many  cases  they  retain  their  porcelain-like  character  even  after  pro-  i 
longed  exposure. 
The  black  shales  Avhich  occur  in  the  upper  levels  of  the  mine  are 
repeated  at  various  depths,  but  in  thinner  layers,  and  finally  give  j 
way  entirely  to  the  greenish  variety. 
Prior  to  the  formation  of  the  ore  body  the  fissures  were  filled  with  i 
a  peculiar  material,  now  consolidated  and  locally  termed  a  "  dike.'  i 
It  consists  of  a  dense,  homogeneous  rock  containing  an  immense  j 
number  of  angular  fragments  of  black  shale  and  other  country  rock  j 
"Trans.  Am.  Inst.  Min.  TOng.,  vol.  30,  1901,  pp.  227-236. 
