THE   CORDILLERAS.  789 
eruptive  rocks  of  the  Oquirrh  Mountains,  and  the  extrusive  andesitic 
lavas  and  tuffs  of  the  Aqui  Mountains  may  be  related. 
Boutwell,53  in  1907,  presents  the  detailed  evidence  observed  by 
him  in  1900,  which  proved  the  intrusive  origin  of  the  Little  Cotton- 
Avood  and  Alta  igneous  masses.  This  includes  apophyses,  dikes,  and 
sills  extending  upward  from  the  parent  igneous  masses  across  the 
bedding  of  overlying  sediments,  the  truncation  of  hundreds  of  feet 
of  sediments,  intense  contact  metamorphism,  etc.  This  was  the  first 
positive,  conclusive,  concrete  proof  of  the  nature  of  these  bodies.  He 
concludes  that  the  igneous  rocks,  considered  by  the  Fortieth  Parallel 
Survey  to  be  Archean,  are  intrusive ;  that  the  main  masses  constitute 
a  series  of  three  or  four  distinct  bodies,  and  that  the  Little  Cotton- 
wood granite  is  post-Cambrian,  the  Alta  body  is  post-Carboniferous, 
and  the  Clayton  Peak  mass  and  the  dikes  of  the  Park  City  district 
are  post-Permian. 
PROMONTORY    RIDGE,    FREMONT    ISLAM).    AM)    ANTELOPE    ISLAM)    RANGES. 
Stansbury,54  in  1853,  states  that  granite,  gneiss,  mica  schist,  slate, 
and  hornblende  rock  occur  at  Antelope  and  Fremont  islands.  On  the 
west  side  of  Fremont  Island  is  a  bold  escarpment  100  feet  high  of  tal- 
cose  slate,  overlain  by  granite  and  gneiss.  On  Promontory  Point  mica 
slate  and  limestone  were  seen. 
Hague,35  in  1877,  finds  the  promontory  of  Great  Salt  Lake  to  con- 
sist of  quartzites  and  mica-bearing  schists  in  a  conformable  series, 
dipping  to  the  west  about  38°,  and  estimated  to  be  3,800  feet  thick. 
In  the  middle  of  the  series  is  a  zone  of  calcareous  sandstone,  within 
which  are  several  beds  of  limestone.  In  the  vicinity  of  Promontory 
station  the  Archean  schists  are  overlain  by  limestones.  On  Fremont 
and  Antelope  islands  are  outcrops  of  Archean  rocks.  The  outcrop  on 
Fremont  Island  consists  of  hornblendic  and  micaceous  gneisses,  dip- 
ping to  the  west,  while  that  of  Antelope  Island  is  mostly  gneisses, 
with  some  quartzites  and  mica  slates,  one  of  these  beds  becoming  cal- 
careous and  approaching  a  limestone. 
RAFT    RIVER    RANGE. 
Hague,35   in    1877,  describes  a  considerable  body  of  structureless 
idium-g: 
tral  mass. 
medium-grained  granite  in  the  Raft  River  Range,  forming  the  cen 
SUMMARY   OF  PRESENT  KNOWLEDGE. 
Pre-Cambrian  rocks  appeal-  in  the  Uinta  and  Wasatch  mountains 
and  in  certain  of  the  Basin  ranges — -Promontory  Ridge,  Fremont 
Island,  Antelope  Island,  and  Raft  River  Mountains. 
Uinta  Mountains. — Occupying  a  large  part  of  the  area  of  the  east- 
west  Uinta  anticline  is  a  great  series  of  sedimentary  rocks,  estimated 
