604  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
mation.  The  crevice  is  in  part  filled  by  a  deposit  of  gypsum,  which 
varies  from  2  to  3  inches  in  width  and  resembles  the  veins  already 
noticed.  The  flow  from  these  lower  springs  is  copious,  has  a  sul- 
phurous taste,  is  remarkably  soft,  and,  as  far  as  observed,  does  not 
form  a  surface  deposit  outside  of  the  fissure,  not  even  in  the  channels 
lined  with  brown  and  red  algse,  a  growth  which  is  abundant  in  the 
overflow  and  forms  silk-like  skeins  in  the  easternmost  spring.  The 
water  is  palatable  and  is  largely  drunk  by  the  guests  at  the  hotel. 
It  is  probable  that  the  rock  walls  of  the  fissures  from  which  the 
waters  of  the  Hunters  Hot  Springs  now  issue  have  long  since  been 
leached  of  the  more  readily  soluble  material.  The  rocks  are  com- 
posed of  small  fragments  of  andesite,  the  fine  dust  of  a  volcanic 
eruption  washed  into  the  waters  of  a  great  lake  which  at  one  time 
covered  this  region  and  extended  westward  to  the  flanks  of  the 
Bridger  Mountains.  As  the  hot  waters  come  up  through  these  rocks, 
it  would  be  expected  that  the  older  deposit  would  contain  an  abun- 
dance of  silica,  but  no  such  deposit  has  been  found.  The  material 
consists  mainly  of  sulphate  of  lime.  The  stilbite,  which  is  a  mono- 
clinal  zeolite,  though  a  contemporaneous  deposit,  is  mainly  the  prod- 
uct of  the  later  or  dying  stages  of  hot-spring  action.  The  tempera- 
ture of  the  water  is  148°  F.  No  official  analysis  has  been  made,  but 
the  accompanying  analysis,  made  for  the  owners  of  the  springs  by  Mr. 
Harry  Snyder  and  published  on  their  letter  heads,  is  given  herewith : 
Analysis  of  water  from  Hunters  Hot  Springs,  Montana. 
Temperature °   F__       148 
Mineral  matter grains—  16.  28 
Silica per  cent—  17.  03 
Alumina do 2.82 
Lime do .75 
Magnesia  do .  75 
Chlorine : do 3.  62 
Potash    do 1.60 
Soda   do 44.02 
Combined  carbon  dioxide do 15.51 
Combined  water do 10.  25 
Sulphates do .  88 
Lithium Trace. 
Gases  in  solution : 
Free  carbon  dioxide per  cent—  49 
Dissolved  oxygen grams  per  liter—       .0416 
As  stilbite  contains  57.4  per  cent  silica,  16.3  per  cent  alumina,  7.7 
per  cent  lime,  and  1.4  per  cent  soda,  with  17.2  per  cent  water,  it  is 
probable  that  the  spring  water  is  now  depositing  this  mineral,  and 
not  gypsum,  but  this  could  not  be  verified. 
