602  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
whose  snow-covered  peaks  rise  to  heights  of  11,000  feet  at  a  distance 
of  only  10  miles  to  the  north. 
The  country  in  the  immediate  vicinity  of  the  springs  is  relatively 
gently  rolling,  there  being  a  succession  of  hills  and  long  ridges,  with 
intervening  swales,  carrying  intermittent  streams.  The  Sheep  Cliffs, 
or  Sheep  Mountain,  an  abrupt  sandstone  cliff  capped  by  intrusive 
trap  sheet,  lies  about  4  miles  to  the  Avest.  The  gentle  foothill  region 
of  the  Crazy  Mountains  is,  in  this  vicinity,  somewhat  barren  in 
aspect,  having  a  scanty  growth  of  grass,  with  occasional  low  sage- 
brush. At  the  immediate  vicinity  of  the  springs  the  main  drainage 
channel  carries  flowing  water,  and  a  fine  growth  of  cottonwoods 
forms  a  pleasant  park.  With  the  exception  of  the  alluvial-filled 
stream  bottoms,  the  country  has  too  scanty  a  soil  to  be  useful  for 
agriculture. 
The  rocks  in  this  neighborhood  are  all  part  of  the  Livingston  for- 
mation, which  is  composed  of  dark-colored,  poorly  assorted  sandstone- 
like rocks  made  up  mainly  of  volcanic  debris,  and  represents  the 
finer  material  ejected  from  the  volcanoes  of  the  region  to  the  south, 
which  were  active  in  early  Eocene  time.  These  rocks  have  been 
folded,  and  the  hot-spring  fissures  are  on  the  summit  of  an  anticlinal 
fold  with  a  northeast  axis,  while  the  igneous  masses  of  the  Crazy 
Mountains  send  out  innumerable  dikes,  some  of  which  reach  almost 
to  the  vicinity  of  the  springs.  These  dikes  are  radial  from  the 
mountains,  and  if  extended  to  the  springs  would  cut  across  the  folded 
rocks  at  an  acute  angle  with  the  axis  of  the  main  anticline,  In  fact, 
a  fault  observed  in  the  canyon  of  the  Yellowstone  appears  to  extend 
northward,  passing  almost  through  the  location  of  the  springs. 
These  hot  springs  are  connected  with  reefs  or  veins  composed  of 
gypsum,  with  stilbite,  The  more  prominent  of  these  reefs  are  seen  in 
the  ridges  to  the  northwest  of  the  springs,  which  are  now  dry,  but  the 
existing  hot  waters  come  from  a  similar  vein,  and  their  complete 
resemblance  and  connection  with  the  older  and  now  dry  veins  is 
quite  apparent.  These  veins  occupy  fractures  traversing  upturned 
beds  of  arkose,  grits,  sandstones,  and  shales,  all  of  them  dark-colored 
rocks  which,  as  already  noted,  are  composed  of  volcanic,  andesitic 
debris,  forming  a  part  of  the  Livingston  series,  a  post-Laramie  fresh- 
water formation.  The  veins  outcrop  in  white  reefs,  which  form  a 
conspicuous  feature  of  the  grassy  slopes,  and  are  in  strong  contrast 
to  the  dark-colored  rocks  of  the  ridges.  There  are  three  of  these  reefs. 
The  two  westernmost  are  about  a  quarter  of  a  mile  apart,  and 
approach  each  other  to  the  north.  The  middle  vein,  which  is  the 
largest,  has  a  course  of  N.  60°  W.  The  vein  to  the  west  of  it  runs 
nearly  northwest,  while  the  eastern  vein  is  parallel  to  the  middle  one. 
As  just  noted,  the  rocks  are  upturned,  the  dip  varying  from  5°  to  20°  7 
