842  PRE-CAMBKTAN    GEOLOGY   OF    NORTH    AMERICA. 
micaceous  and  chloritic  schists,  which  denote  the  original  planes  of 
stratification.  It  is  believed  that  by  a  careful  examination  evidence 
will  be  found  bearing  upon  the  former  condition  of  this  metamorphic 
area.  The  Wind  River  Range  is  regarded  as  a  steep  anticlinal  fold. 
The  rocks  constituting  it  are  regarded  as  representing  siliceous  shales 
(schists)  and  are  more  or  less  argillaceous  sandstones  (granites).  On 
the  eastern  side  of  the  Wind  River  Range  is  found  hard,  red,  quartz- 
itic  sandstone  directly  overlying  the  youngest  metamorphic  granites. 
It  extends  up  the  gently  sloping  ridges  in  a  scalloped  line.  In  direct 
contact  with  the  granites  it  is  difficult  to  determine  where  the  granite 
ends  and  the  quartzite  begins,  so  that  it  may  be  said  that  the  quartzites 
and  granites  blend  into  each  other.  It  appears  that  the  lowest  Silu- 
rian strata  were  deposited  before  the  thorough  metamorphism  of  the 
entire  mass  took  place,  unless  the  change  in  the  sandstone  was  caused 
by  generation  of  heat  during  the  period  of  mountain  elevation. 
The  Archean  rocks  of  the  Wind  River,  Sweetwater,  and  adjacent 
ranees  are  classified  into  the  Huronian,  Laurentian,  and  Prozoic  svs- 
tenis.  The  first  includes  micaceous,  hornblendic,  and  chloritic 
granite,  30,000  feet  thick.  The  Laurentian  includes  metalliferous 
schists  composed  of  quartz,  feldspar,  hornblende,  and  mica,  18,000 
feet  thick.  The  Prozoic  includes  massive  structureless  muscovite 
granite  of  indefinite  thickness. 
Peale,37  in  1879,  states  that  the  western  foothills  of  the  Wind 
River  Mountains  and  a  few  isolated  buttes  are  composed  of  muscovite 
granite,  the  most  prominent  of  the  latter  being  Fremonts  Butte. 
St.  John,117  in  1883,  describes  the  Archean  rocks  of  the  Wind 
River  Range  and  gives  a  number  of  sections  showing  the  unconform- 
able relations  of  these  rocks  to  the  overlying  Potsdam  and  higher 
sedimentaries.  The  Archean  area  is  composed  of  granitic,  gneissic, 
and  various  schistose  rocks,  including  hornblendic,  micaceous,  talcose, 
and  garnetiferous  varieties. 
GROS   VENTRE   AND   WYOMING   RANGES. 
St.  John,118  in  1879,  states  that  the  Gros  Ventre  Range  has  an 
Archean  nucleus,  consisting  chiefly  of  distorted  gneissic  and  schistose 
layers,  and  forms  a  sort  of  transverse  bar  or  truss  connecting  the 
Wind  River  and  Teton  ranges.  The  Primordial  quartzite  was  seen 
lying  in  immediate  contact  unconformably  above  the  Archean  schists, 
from  which  it  is  separated  by  a  rose-colored,  finely  laminated  gneissoid 
layer,  which  may  be  the  metamorphosed  basal  member  of  the  quartzite. 
St.  John,117  in  1883,  further  describes  the  Gros  Ventre  Range  and 
gives  various  sections  through  it.  The  Primordial  quartzite  rests 
directly  upon  the  Archean  rocks.  In  the  Wyoming  Range,  as  in  the 
Gros  Ventre  Range,  the  Archean  is  unconiormably  below  the  strati- 
fied rocks. 
