ihvinc,.]  OURAY    DISTRICT,   COLORADO.  57 
of  the  Uncompahgre  Valley  about  4  miles  north  of  Ouray,  the  chief 
mines  being  the  Newsboy  and  Black  Girl.  A  few  minor  develop- 
ments, as  yet  only  of  prospective  value,  occur  on  the  uplands  lying 
west  of  the  river,  among  which  the  Gem  and  Teller  mines  might  be 
mentioned  as  the  most  important. 
The  veins  are  fissures  in  the  country  rock  filled  with  high-grade 
ores  of  silver  and  the  gangue  minerals  which  accompany  them.  The 
strike  of  the  fissures  is  in  general  quite  uniform,  approximating  an 
east-west  direction.  Thus  in  the  Bachelor  mine  the  strike  is  N.  83° 
E.;  in  the  Black  Girl  it  is  N.  85°  E.,  and  in  the  Calliope  N.  83°  E. 
The  dip  of  the  fissures  varies  from  a  vertical  position  to  about  60°. 
Instances  of  a  dip  of  45°  are  known,  but  are  rather  uncommon.  The 
fissures  usually  show  a  slight  displacement,  rarely  reaching  as  much 
as  7  feet  and  generally  so  small  as  to  be  distinguished  only  by  close 
observation.  The  width  varies  from  a  few  inches  to  as  much  as  8 
feet,  a  fair  average  being  about  3  feet.  Most  of  the  veins  are  rather 
uniform  and  retain  their  width  for  the  larger  portion  of  their  course 
without  marked  variation  although  pinches  and  swells  are  to  be 
observed  in  many  parts  of  the  mines. 
The  country  rock  in  which  the  veins  occur  is  the  varied  series  of 
sedimentary  rocks  lying  below  the  andesite  breccia  cap  and  compris- 
ing from  above  downward : 
1.  Mancos  black  shale. 
2.  Dakota  qnartzite  and  sandstones  alternating  with  black  shale. 
3.  A  highly  varied  series  of  clay  shales,  sandstones,  sandy  shales,  calcareous 
shales  and  limestones,  belonging  to  the  McElmo  group  of  the  Jurassic. 
4.  Red  sandstones  and  conglomerates  with  some  reddish  shales. 
These  sediments  have  as  a  whole  a  gradual  downward  inclination 
toward  the  north  by  east,  which  eventually  brings  them  down  across 
the  bed  of  the  Uncompahgre  River  along  its  northward  course.  The 
dip  in  undisturbed  localities  is  about  10°.  Local  disturbances  have 
sometimes  increased  or  reversed  these  dips,  as  in  the  Bachelor  mine, 
where  the  strata  dip  southeastward  at  an  angle  of  about  10°.  Steeply 
inclined  beds  occur  only  in  a  few  of  the  mines.  The  beds  at  the 
Calliope  and  Iowa  Chief  mines  dip  southeastward  at  an  angle  of  about 
25°,  but  this  inclination  holds  good  for  only  a  limited  area.  In  some 
places  the  ore  is  contained  within  two  fairly  well-defined  walls;  in 
others  the  fissure  is  divided  into  branches  that  separate  from  and 
unite  with  one  another  many  times.  Cross  fractures  further  unite 
the  divided  branches,  so  that  the  resulting  network  often  passes  into 
a  more  or  less  breccia  ted  structure. 
Relation  of  the  fissures  to  the  wall  rock. — The  relation  of  the  ore 
in  the  fissures  to  the  wall  rock  is  peculiar.  The  ore  is  much  more 
abundant  and  of  very  much  higher  grade  when  included  between 
walls  of  quartzite,  and  is  either  absent  or  of  a  low  grade  when  the 
