100  CONTRIBUTIONS    TO   ECONOMIC    GEOLOGY,  1904.        [bull.  2<l< 
well  as  a  silver  camp.     The  high  average  value  of  the  silver  ores  ii 
the  vicinity  of  Silver  Plume  and  Georgetown  also  caused  the  resumf 
tion  of  mining  in  these  localities.     The  average  value  per  ton  for  a 
the  silver  ore  shipments  from  the  Silver  Plume  region  from  1891  t 
1902  is  reported  to  be  $96.° 
The  Georgetown  district  is  one  of  the  oldest  mining  districts  ( 
Colorado  and  has  been  almost  constantly  worked  since  the  first  di 
covery  of  precious  metal   in  it;   consequently  it  is  one  of  the  be 
exploited  mining  camps  in  the  country.  .  The  writers  have  not  bee 
able  to  ascertain  even  approximately  the  total  yield  of  the  distric 
for  official  reports  have  usually  been  made  on  the  Avhole  of  Cle; 
Creels  County,  or  even  on  Clear  Creek  and  Gilpin  counties  combine 
Clear  Creek  County  includes,  besides  the  region  treated  in  this  papt 
the  Idaho  Springs  district,  as  well  as  a  number  of  smaller  ares 
Although  there  are  no  reliable  records  to  be  obtained  from  most 
the  mines,  the  total  production  has  certainly  been  many  millions 
dollars. 
Prospecting  and  mining  are  chiefly  prosecuted  through  tunne< 
This  is  because  the  steepness  of  the  mountains  makes  the  situati 
ideal  for  the  employment  of  this  economic  method  of  extraction  a 
drainage. 
The  value  in  the  ores  are  in  silver,  gold,  lead,  zinc,  and  copp 
These  metals  occur  in  different  localities  in  an  infinite  variety  of  p 
centage  combinations.  The  result  is  numerous  chemically  distil 
but  intergrading  groups  of  veins.  The  gold,  although  occasiona 
occurring  native,  is  usually  associated  with  chalcopyrite  or  cop} 
bearing  pyrites.  The  occasional  occurrence  of  gold-bearing  teliuri 
as  in  the  Griffith  mine  at  Georgetown,  is  exceptional.  The  silvei 
often  associated  with  tetrahedrite  ("gray  copper").  It  also  of1 
occurs  in  independent  silver  compounds,  such  as  polybasite,  arg 
tite,  and  ruby  silver,  though  the  last  two  are  not  very  common, 
galena  of  the  district  is  typically  argentiferous  to  a  greater  or  I 
extent,  as  is  also  to  a  less  degree  the  blende.  Of  the  precious  met  I 
silver  occurs  predominantly  betwTeen  Silver  Plume  and  Georgeto  I 
and  gold  between  Georgetown  and  Empire.  At  Silver  Plume  I 
values  are  silver  with  practically  no  gold;  at  Empire  gold  with  p  | 
tically  no  silver. 
TOPOGRAPHY. 
The  lofty,  rugged  mountains  around  Georgetown  are  spurs  of  |< 
main  ridge  forming  the  Continental  Divide,  which  runs  along  I 
western  boundary  of  Clear  Creek  County.  The  mountains  ris  I 
heights  ranging  between  11,000  and  14,000  feet.    Grays  Peak,  in  |< 
"By  Mr.  J.  II.  Eaton,  Silver  Plume. 
