600  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
The  deposits  of  the  Boulder  Hot  Springs  have  been  described  in 
detail  by  the  writer  and  appear  identical  in  character  with  the  silver 
and  gold  bearing  quartz  veins  so  abundant  throughout  the  region 
between  Butte  and  Helena,  Mont." 
In  the  rhyolite  about  the  Monarch  Geyser,  Norris  basin,  Yellow- 
stone Park,  veins  of  gold-bearing  pyrite  are  formed  by  hot  waters. 
Indeed,  the  Yellowstone  Park  otters  a  most  inviting  field  for  the 
study  of  the  relations  between  hot  springs  and  ore  deposition.  Sev- 
eral springs  at  the  Hot  Lake  group,  Lower  basin,  are  depositing  con- 
siderable amounts  of  manganese  oxide,  and  at  the  Ocher  Springs 
deposits  of  limonite  (red  oxide  of  iron)  are  being  formed,  while  the 
deposition  of  realgar  and  orpiment  (the  red  and  yellow  sulphides  of 
arsenic)  at  the  Norris  basin,  has  already  been  described.^ 
THE  LIMONITE  AND  TRAVERTINE  DEPOSITS  OF  THE  ANACONDA 
HOT  SPRINGS,  MONTANA. 
For  a  number  of  years  the  limonite  deposits  found  on  the  foot- 
hills between  Mill  Creek  and  the  city  of  Anaconda  were  quarried 
and  the  ore  shipped  to  the  East  Helena  smelter.  In  1902  the  prop- 
erty was  investigated  by  Mr.  H.  V.  Winchell,  chief  geologist  of  the 
Anaconda  Copper  Company.  He  kindly  took  the  writer  over  to 
see  the  property,  and  called  attention  to  its  unique  character.  It  is 
now  owned  by  and  forms  an  important  source  of  flux  for  the  Washoe 
copper  smelter,  which  lies  but  a  half  mile  or  so  to  the  north. 
The  Anaconda  Hot  Springs  are  3  miles  from  Anaconda,  on  the 
hillside  south  of  the  great  Washoe  smelting  plant  and  west  of  the  Deer 
Lodge  Valle}7.'  The  area  of  former  and  existing  hot-spring  action 
covers  the  slope  north  of  Mill  Creek  and  west  of  the  main  valley, 
the  old  travertine  terraces  of  this  place  being  formerly  as  extensive 
as  the  famous  ones  of  the  Mammoth  Hot  Springs  of  the  Yellowstone 
Park.  Prolonged  degradation  has  removed  the  larger  part  of  the 
Anaconda  deposit  and  destroyed  all  the  terracing.  The  underlying 
rocks  are  tilted  Mesozoic  limestones,  which  are  probably  of  Jurassic 
age,  but  which  have  not  been  identified  by  fossils.  Their  eroded  sur- 
face is  covered  by  rhyolitic  tuffs,  on  which  the  travertine  cap  was 
laid  down. 
The  existing  waters  are  tepid,  inert,  and  feebly  charged,  and  are 
incapable  of  adding  to  the  great  deposit  of  travertine  that  once  cov- 
ered the  slopes.  Several  old  cones  still  exist,  and  from  an  isolated 
one  to  the  northwest  of  the  main  area  a  small  quantity  of  warm 
water  overflows.     There  is  another  cone  to  the  extreme  southwest, 
"  Weed,  W.  H.,  the  Boulder  Hot  Springs,  Mont.  :  Twenty-first  Ann.  Kept.  U.  S.  Geol. 
Survey,  pt.  2,  1900,  p.  227. 
b  Weed  and  Pirsson,  Am.  Jour.  Sci.,  3d  series,  vol.  42,  1895,  p.  401. 
