vanhise.)  ME    CORDILLERAS.  283 
ETayden,21  iii  1873,  gives  many  additional  facts  with  reference  to  the 
occurrence  of  Atelieaii  rocks  in  southwestern  Montana  and  adjacent 
regions.  The  mountain  range  east  of  the  Yellowstone,  supposed  to  be 
mostly  of  igneous  origin,  has  the  characteristic  granitic  nucleus  com- 
mon to  the  mountain  ranges  of  the  region.  In  ascending  the  lower 
canyon  of  the  Yellowstone  the  first  ridge  is  composed  mostly  of  meta- 
morphic  quartzite,  the  second  of  mica-schists  and  granitoid  gneiss.  The 
ribboning  and  banding  of  the  gneiss  is  quite  remarkable  for  its  perfec- 
tion and  regularity.  Granitic  rocks  constitute  the  nucleus  of  the  Yel- 
lowstone range  and  make  up  a  rugged  granite  range  east  of  Olarks 
fork.  At  Henrys  lake  and  Tahgee  pass  the  quartzites  and  gneissic 
rocks  appear  beneath  the  limestones.  The  lower  portion  of  the  un- 
changed rocks  are  pebbly  arenaceous  sandstones  and  limestones  con- 
taining pebbles  which  are  much  worn  and  are  either  quartz  or  micaceous 
gneiss,  showing  that  the  sediments  were  derived  directly  from  the 
metamorphic  rocks.  The  lowest  strata  of  unchanged  rocks  are  here 
regarded  as  Silurian,  and  probably  Potsdam,  although  no  organic 
remains  were  found.  The  Carboniferous  limestones  higher  up  are  filled 
with  characteristic  fossils.  In  the  Middle  canyon  of  the  Madison  the 
stratified  rocks  are  also  believed  to  belong  to  the  Potsdam  epoch, 
although  no  fossils  were  found  lower  than  the  Carboniferous,  and  here 
the  unconformable  relations  of  the  limestones  to  the  met  amor  phic  rocks 
are  clearly  shown.  On  both  sides  of  the  Madison  there  is,  in  restricted 
localities,  an  enormous  development  of  very  hard  gray  quartzitic  sand- 
stone, apparently  partially  metamorphosed,  which  evidently  forms  the 
underlying  rocks  of  the  sedimentary  strata  resting  on  the  strictly  meta- 
morphic  gneiss.  No  organic  life  has  been  found,  yet  it  undoubtedly 
belongs  to  the  oldest  Silurian.  Along  the  valley  of  the  Madison,  be- 
low the  mouth  of  Cherry  creek,  for  several  miles  there  are  successions 
of  gneissic  beds  thousands  of  feet  in  thickness,  Avhich  show  great  vari- 
ety of  composition  and  flexures  in  the  bedding.  In  this  gneiss  are 
layers  of  black  hornblende  gneiss  4  to  6  feet  thick,  which  appear  as 
though  they  were  intrusions  of  trap.  Near  Helena  the  sedimentary 
beds  overlying  the  granite  are  tilted  from  20°  to  45°  past  a  vertical. 
The  Avork  of  reducing  the  metamorphic  strata  which  underlie  the  entire 
country  to  a  system  and  connecting  them  over  extended  areas  has  not 
been  attempted,  and  it  seems  to  the  author  an  almost  hopeless  as  well 
as  a  fruitless  task. 
Peale,22  in  1873,  describes  at  many  localities  crystalline  rocks  in 
southwestern  Montana  and  adjacent  regions.  Gneissic  and  granitic 
rocks  are  mentioned  in  the  Cinnabar  mountains,  in  the  rocks  of  the 
Third  canyon  of  the  Yellowstone,  at  Elk  creek,  at  the  junction  of  the 
two  forks  of  the  Yellowstone,  at  West  Gallatin  canyon,  Bozeman 
creek,  and  other  localities.  Upon  one  of  the  head  waters  of  the  Madison 
are,  found  quartz- schists  and  chlorite-schists,  below  which  in  apparent 
conformity  are  layers  of  limestone.     Still  below  these  are  Carboniferous 
