96  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         T  bull.  260. 
have  carried  down  a  part  of  the  auriferous  contents  of  those  portions 
of  the  lodes  now  removed  by  erosion  and  have  enriched  originally 
lean  pyritic  ores  by  the  secondary  deposition  of  gold  and  silver 
tellurides  and  argentiferous  tetrahedrite,  with  associated  gangue 
minerals. 
Careful  study  of  the  Cripple  Creek  ore  deposits  has  failed  to  dis- 
cover that  the  hypothesis  of  secondary  enrichment  is  supported  by 
crucial  evidence.  The  minerals  are  not  arranged  in  any  discoverable 
definite  sequence,  nor  does  the  present  investigation  find  much  to  sup- 
port the  view  that  the  rich  telluride  ores,  as  a- rule,  pass  with  increas- 
ing depth  into  low-grade  pyritic  ores.  Frequently  such  ore  as  occurs 
below  a  depth  of  1,000  feet  is  precisely  the  same  in  character  as  ore 
found  within  100  feet  of  the  surface.  Tetrahedrite,  which  has  been 
regarded  by  some,  without  definite  proof,  as  a  secondary  mineral, 
occurs  sporadically  throughout  the  district  and  at  all  depths  reached 
by  present  workings.  The  richest  ore  does  not  uniformly  occur  imme- 
diately below  the  oxidized  ore.  There  is,  in  fact,  little  indication  of 
enrichment  in  the  oxidized  zone  such  as  is  so  often  found  in  gold- 
quartz  veins  of  the  normal  type.  Frequently  the  fresh  telluride  ore 
is  extremely  rich,  and  high-grade  pockets  occur  impartially  in  oxi- 
dized and  fresh  portions  of  the  veins.  Neither  would  it  be  correct  tc 
say  that  there  is  a  gradual  decrease  in  the  value  of  ore  in  depth.  Il 
is  quantity,  not  value,  which  decreases. 
While  it  is  certain  that  pyrite,  and  possibly  other  minerals,  ha: 
formed  at  more  than  one  period  during  the  mineralization  of  the  dis 
met,  and  while  it  is  equally  clear  that  in  general  the  rich  telluride 
were  the  last  of  the  ore  minerals  to  be  deposited,  there  is  apparent]; 
no  evidence  that  any  one  of  these  minerals  has  been  formed  by  enrich 
ing  solutions  at  the  expense  of  primary  minerals.  So  far  as  definite 
conclusion  is  warranted  in  an  investigation  as  yet  incomplete,  i 
appears  that  the  unoxidized  ore  deposits  of  the  Cripple  Creek  distric 
represent  the  product  of  one  general  period  of  mineralization  and  tha 
they  have  not  been  appreciably  modified  by  secondary  enrichmer 
during  the  subsequent  erosion  of  the  region. 
UNDERGROUND    WATER. 
The  conditions  of  underground  waters  are  unusual.  A  dry  climal 
and  a  heavy  percentage  of  run-oft'  minimize  the  annual  additions  1 
the  underground  supply.  Nevertheless,  the  ground-water  level  is  n< 
unusually  deep,  and  large  quantities  of  water  are  encountered  in  a 
the  mines  below  that  level.  The  original  water  surface  of  the  distri 
in  the  volcanic  rocks  stood  at  elevations  of  9,J:00  to  9,700  feet,  or  1( 
to  GOO  feet  below  the  surface  of  the  ground.  At  first  pumping  w; 
commenced  by  individual  mines,  but  it  was  soon  found  that  the  radii 
