284  PRE-CAMBRTAN    ROCKS    OF    NORTH    AMERICA.  [bull. 86. 
limestones.  The;  whole  is  Relieved  to  be  an  overturn.  Between  Red 
Rock  lake  and  Henry  lake  is  an  exposure  of  quartz-schist  flipping  to 
the  southwest  at  an  angle  of  20°,  estimated  to  be  2,000  feet  in  thick- 
ness, which  is  believed  to  rest  directly  npon  the  granite.  On  Cherry 
creek  the  gneissic  rocks  are  succeeded  by  beds  of  massive  quartzite, 
shale,  limestones,  etc.,  resting  un conformably  upon  them,  the  latter 
being  probably  Lower  Silurian. 
Hayden,23  in  1876,  describes  some  geological  sections  about  the 
headwaters  of  the  Missouri  and  Yellowstone  rivers.  There  is  an  anti- 
clinal axis  between  the  Madison  and  Jefferson  which  has  a  granitic 
nucleus,  and  on  the  east  side  of  the  Gallatin  the  Silurian  rocks  rest 
upon  granitic  hills. 
Holmes,24  in  1883,  describes  the  Silurian  strata  as  resting  npon  the 
metamorphic  rocks  at  Cinnabar  mountains.  The  butte  at  Bear  gulch 
is  composed  of  vertical  shales,  and  these  are  underlain  by  metamorphic 
quartzites.  Between  the  butte  and  Junction  valley  are  hard  meta- 
morphic quartzites  and  qnartzitic  schists  which  not  improbably 
consist  chiefly  of  altered  and  distorted  Paleozoic  or  Mesozoic  strata, 
but  there  is  bnt  slight  resemblance  to  these  formations.  The  ridge 
near  the  canyon  of  Bear  creek  is  composed  of  schists  that  have  a 
decided  qnartzitic  character.  The  East  Gallatin  range  is  largely  of 
granite.  At  different  places  the  Archean  granites  are  unconformably 
overlain  by  the  Silurian. 
Davis,25  in  1880,  describes  Archean  rocks  as  occurring  in  the  neigh- 
borhood of  Neihart,  about  the  headwaters  of  Belt  creek  in  the  LiUle 
Belt  mountains.  They  are  dark  reddish  and  gray  gneisses  with  the 
folia  generally  at  steep  angles,  cut  by  granitic?  eruptions  that  were  not 
found  to  extend  into  the  overlying  bedded  rocks.  The  Paleozoic  series 
begins  with  a  vast  series  of  Lower  Cambrian  barren  slates,  at  least  10,000 
or  15,000  feet  thick  at  many  places.  The  slates  are  capped  by  hard  sand- 
stone or  quartzite,  100  or  150  feet  thick,  persistent  throughout  the  area 
examined,  which  is  overlain  by  an  equally  persistent  trilobitie  lime- 
stone 100  to  300  feet  thick  clearly  of  Potsdam  date.  With  the  upper 
members  of  these  slates  are  found  diabasic  eruptions.  These  lower 
Cambrian  slates  are  found  in  the  main  range  at  Cadottes  pass,  in  the 
Big  Belt  mountains,  and  in  the  Little  Belt  range.  In  the  sections  the 
Archean  rocks  at  Little  belt  are  represented  as  resting  unconformably 
below  the  Lower  Cambrian  slates,  while  on  the  Bridger  range  they  are 
placed  in  conformity  with  the  slates. 
Peale,26  since  1884,  has  been  working  on  the  "Three  Porks  Sheet" 
of  Montana  (the  square  degree  included  between  111°  and  112°  of  lon- 
gitude and  15°  and  46°  of  latitude).  In  the  northern  part,  in  the 
Bridger  range,  of  this  area  is  found  Archean  gneisses. 
Other  Archean  areas  are  the  one  extending  north  of  Virginia  city 
some  28  miles,  in  which  a  body  of  eruptive  granite  occurs,  and  the  one 
bordering  the  canyon  of  the  Madison.     The  gneiss  of  the  Madison  can- 
