THE   CORDILLERAS.  843 
TETON,  ABSAROKA,  SNOWY,  AND  GALLATIN  RANGES  SURROUNDING  YELLOW- 
STONE   PARK." 
Bradley,47  in  1873,  describes  the  central  nucleus  of  the  Teton 
Mountains  as  consisting  of  granites,  gneisses,  and  schists,  which  vary 
greatly  in  character.  No  rock  succession  was  ascertained.  The 
granite  is  in  thick  solid  beds  and  the  other  rocks  are  much  broken  and 
tilted  in  various  ways,  and  are  crossed  in  every  direction  by  innumer- 
able large  and  small  veins,  mostly  of  quartz,  but  a  few  of  granite. 
There  is  a  general  strike  in  an  east- west  direction.  Traplike  rocks 
are  interlaminated  with  the  gneiss  and  granite,  which  suggests  that 
they  may  be  dikes,  but  they  are  evidently  conformable  with  the  layers 
and  were  either  contemporaneous  sheets  or  else  subsequent  intrusives. 
St.  John,11*  in  1879,  describes  Archean  rocks  fls  constituting  the 
nucleal  ridge  of  the  Teton  Mountains.  The  major  portion  of  them 
are  metamorphics  of  a  gneissic  or  schistose  variety.  The  Archean 
strata  of  the  Teton,  Wyoming,  and  Gros  Ventre  ranges  are  divided 
into  Huronian  and  Laurentian.  With  the  former  are  placed  the 
quartzites  and  micaceous  and  chloritic  slates,  forming  heavy  deposits 
several  thousand  feet  in  thickness  and  developed  only  in  the  south- 
west, while  with  the  Laurentian  are  the  gneisses,  various  schistose 
rocks,  and  granite.  In  the  southwestern  part  of  the  Teton  district 
is  a  narrow  tongue  of  quartzites  which  are  placed  with  the  Primordial, 
but  may  be  Huronian. 
Hague,  Weed,  and  Iddings,119  in  1890,  map  and  describe  the  geology 
of  the  Yellowstone  National  Park,  Wyoming.  Archean  rock-  are 
found  near  the  borders  of  the  district,  in  the  mountain  ranges  which 
encircle  the  park  plateau.  They  comprise  granites,  gneisses,  and 
schists.  The  granites  and  gneisses  are  for  the  most  part  coarsely 
crystalline,  and  the  entire  series  shows  the  effect  of  metamorphism  by 
pressure. 
Algonkian  rocks  are  recognized  only  in  the  southern  end  of  the 
park,  and  are  best  exposed  on  the  southern  slope  of  Mount  Sheridan, 
from  which  the  formation  has  been  called  the  Sheridan  quartzite. 
The  formation  comprises  sandstones  and  slates,  which  contain  no  fos- 
sils. Unconformably  overlying  the  Sheridan  quartzite  i-  the  Ellis 
(Juratrias)  limestone.  The  assignment  of  the  formation  to  the 
Algonkian  is  based  largely  on  the  fact  that  similar  rock-  arc  unknown 
in  the  Paleozoic  series,  and  on  the  fact  that  no  sedimentary  rock- 
older  than  these  quartzites  are  exposed  in  this  district. 
Hague,120  in  1896,  in  a  discussion  of  the  age  of  the  igneous  rocks  of 
the  Yellowstone  National  Park,  mentions  the  occurrence  of  rocks  of 
Archean  age  in  the  surrounding  mountain  ranges.  The  Teton-,  bor- 
dering the  park  to  the  south,  consist    mainly   of  an    Archean    mass, 
"See  also  summary  of  literature  <>f  southwestern  Montana  and  adjacent  parts  <>i'  Wyo- 
ming, under  section  i),  pp.  853-863. 
