278  PRE-CAMBRIAN   ROCKS    OF    NORTH    AMERICA.  [bull. 88. 
Hayden,11  in  1868,  states  that  the  unconformity  between  the  crys- 
talline and  unmetamorphosed  strata  at  the  Big-  Horn  mountains  is 
very  apparent, 
Carpenter,12  in  1878,  describes  the  Big  Horn  range  as  composed  at 
the  base  of  thick  masses  of  Primordial  sandstone  resembling  the  Pots- 
dam sandstone  of  the  Black  hills,  although  the  heat  coeval  with  the 
upheaval  of  the  mountains  has  probably  obliterated  the  fossils  which 
are  so  abundant  in  that  region.  The  sandstone  rests  un  conform  ably 
against  the  Archean,  is  inclined  from  the  flanks,  is  folded,  and  in  many 
places  is  upturned  as  in  the  Black  hills  and  Colorado  mountains.  Above 
the  sandstone  is  a  limestone  containing  numerous  easts  of  tipirifer  cam- 
eratus.  The  crystalline  rocks  appear  at  an  elevation  of  about  9,000 
feet  and  compose  the  higher  parts  of  the  range.  Near  the  summit 
fine  grained,  grayish  granite  predominates,  occasionally  varied  by 
various  patches  of  mica-schist.  The  Owl  creek  mountains  are  com- 
posed of  porphyritie  granite  rich  in  feldspar,  which  give  place  at  higher 
elevations  to  a  gneissoid  granite.  They  connect  the  southern  end  of 
the  Big  Horn  mountains  with  the  northern  part  of  the  Wind  river 
range. 
LITERATURE   OF   THE   RATTLESNAKE   MOUNTAINS. 
Engelmann,5  iii  1876,|states  that  granites  and  granitic  syenites  which 
are  regarded  as  igneous  rocks  form  a  large  part  of  the  Rattlesnake 
mountains. 
LITERATURE   OF   THE   SWEETWATER  AND  ADJACENT  MOUNTAINS. 
Ball,13  in  1835,  notes  granitic  rocks  along  the  Sweetwater. 
Hayden,11  in  18G8,  mentions  granites  and  syenites  as  occurring  in 
the  Sweetwater  mountains. 
Engelmann,5  in  187G,  places  the  crystalline  schists  between  the  three 
crossings  of  the  Sweetwater  and  South  pass,  and  those  on  the  eastern 
slope  of  South  pass  as  metamorphics.  They  include  gneiss,  mica  schist, 
argillaceous  and  siliceous  schist,  and  hornblendic  rocks. 
Endlich,8  in  1879,  describes  in  the  Sweetwater  valley  and  in  ad- 
jacent regions  Prozoic  and  metamorphic  rocks.  In  the  Sweetwater 
hills  are  Prozoic  rocks,  coarse  grained,  structureless  granite,  like  those 
west  of  the  Wind  river  mountains  which  are  cut  by  basaltic  dikes,  but 
which  never  penetrate  the  overlying  younger  rocks.  The  metamorphic 
granite  of  the  Sweetwater  and  Seminole  hills  is  regarded  as  a  con- 
tinuation of  the  youngest  granite  of  the  eastern  slope  of  the  Wind 
river  range.  East  of  Elkhorn  gap  is  found  a  series  of  folded  sedimen- 
tary beds,  upon  both  sides  of  which  is  granite  apparently  of  the  same 
character.  The  northern  and  northwestern  portions  of  the  granite 
hills,  instead  of  being  composed  of  Prozoic  granite,  are  formed  of  strati- 
lied  granites  with  hornblende-schists.  Toward  the  eastern  termination 
the  stratification  is  so  apparent  that  from  a  short  distance  the  rocks 
