THE   CORDILLERAS.  855 
Holmes,140  in  1883,  describes  the  Silurian  strata  as  resting  upon  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  quartzitic  schists,  which  not  improbably 
consist  chiefly  of  altered  and  distorted  Paleozoic  or  Mesozoic  strata, 
though  there  is  but  slight  resemblance  to  these  formations.  The  ridge 
near  the  canyon  of  Bear  Creek  is  composed  of  schists  that  have  a 
decided  quartzitic  character.  The  East  Gallatin  Range  is  largely  of 
granite.  At  different  places  the  Archean  granites  are  unconformably 
overlain  by  the  Silurian. 
Davis,141  in  1880,  describes  Archean  rocks  as  occurring  in  the  neigh- 
borhood of  Neihart,  about  the  headwaters  of  Belt  Creek,  in  the  Little 
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  sandstone  or  quartzite,  100  or  150  feet  thick,  persistent 
throughout  the  area  examined,  which  is  overlain  by  an  equally  per- 
sistent trilobitic  limestone,  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  repre- 
sented as  resting  unconformably  below  the  Lower  Cambrian  slates, 
while  on  the  Bridger  Range  they  are  placed  in  conformity  with  the 
slates. 
Peale,142  in  1803  and  189G,  maps  and  describes  the  geology  of  the 
Three  Forks  quadrangle  in  Montana.  Archean  gneisses  and  Algon- 
kian  sediments  occupy  large  areas.  The  Archean  gneisses  occur  prin- 
cipally in  the  foothills  of  the  Bridger  Range,  the  mountain  masses 
at  the  northern  and  southern  ends  of  the  Madison  Range,  west  of  the 
Madison  Valley  and  north  of  Virginia  City,  the  southern  part  of  the 
Jefferson  Range,  the  foothills  of  the  Gallatin  Range,  south  of  the 
Gallatin  Valley,  and  beneath  the  Bozeman  lake  beds  at  the  southern 
end  of  the  plateau,  between  the  Gallatin  and  Madison  valleys.  The 
rocks  referred  to  the  Archean  may  possibly  include  some  that  eventu- 
ally may  be  referred  to  the  Algonkian.  The  contacts  of  the  Archean 
with  the  overlying  sediment aries  are,  in  all  cases,  unconformable. 
The  Algonkian  series  comprises  two  divisions — the  Cherry  Creek 
beds  and  the  Belt  formation. 
The  Cherry  Creek-  beds  occupy  an  area  of  30  to  10  square  miles  in 
the  foothills  immediately  west  of  Madison  River  and  a  few  miles 
north  of  the  southern  boundary  of  the  quadrangle,  and  also  a  small 
