THE    CORDILLERAS.  815 
King,80  in  1878,  describes  the  Archean  rocks  of  the  Park  Range. 
The  crystalline  body  itself  is  a  single  anticlinal  fold,  of  which  thai 
portion  of  the  range  sonth  of  Pelham  Peak  is  the  westerly  dipping 
half.  The  easterly  dipping  half  shows  only  in  the  extreme  eastern 
foothills  and  in  the  projecting  spur  which  lies  between  Big  Creek 
and  North  Park.  The  main  body,  therefore,  is  the  half  of  an  anti- 
cline, the  other  half  having  suffered  a  deep  downthrow,  which  has 
left  only  traces  of  the  easterly  dip.  The  series  of  Archean  rocks  in- 
volved in  this  fold  are  bedded  granitic  gneisses  of  uniform  constitu- 
tion and  material  but  widely  varied  internal  structure,  hornblendic 
schists,  and  dioritoid  rocks,  besides  limited  quartzites.  Of  Archean 
eruptive  rocks  there  are  none,  unless  some  obscure  dioritic  bodies  are 
intrusive,  and  all  the  evidence  points  the  other  way. 
Emmons  (S.  F.),87  in  1882,  states  that  in  the  Mosquito  Range  are 
found  granites,  gneisses,  and  amphibolites.  The  granites  are  in  most 
cases  stratified  and  are  of  undoubted  sedimentary  origin.  In  other 
cases  the  evidence  is  less  clear  and  they  have  the  characteristics  of 
eruptive  granites.  Within  the  masses  of  the  normal  granite  occur 
large,  irregular,  veinlike  masses,  of  secondary  origin,  corresponding 
to  pegmatite.  The  gneiss  is  mostly  mica  gneiss.  The  amphibolite 
is  less  abundant  than  the  gneiss  and  granite  and  occurs  interstratified 
with  them.  Unconformably  above  these  are  quartzites  which  bear 
Primordial  fossils  belonging  to  the  Potsdam. 
Emmons,88  in  1898,  describes  the  Archean  rocks  of  the  Tenmile 
quadrangle,  in  Colorado.  These  rocks  outcrop  to  the  east  of  Hie 
great  fault — the  Mosquito  fault — running  north  of  Leadville.  They 
consist  of  granites,  granite  gneisses,  mica  schists,  and  amphibolites, 
with  pegmatite  veins  traversing  them  in  every  direction.  Gneisses 
and  schists  are  the  prevailing  types. 
A  small  patch  of  Cambrian  sediment  is  found  resting  unconform- 
ably on  the  Archean  to  the  east  of  the  Mosquito  fault, 
SAWATCH    AND    ELK    RANGES    AND    ADJACENT    PARTS    OE    ARKANSAS    AND 
GUNNISON  VALLEYS. 
TIayden,89  in  1874,  describes  the  Sawatch  Range  as  a  solid  mass  of 
granite,  80  miles  in  length  by  40  in  width,  which  has  acted  as  a  sin- 
gle wedge  thrust  upward,  and  thus  causing  the  sedimentaries  to  in- 
cline from  either  side. 
Peale,63  in  1874,  states  that  on  Massive  Mountain  the  rocks  are 
mainly  gneissic,  with  alternations  of  porphyritic  granite  or  granite 
porphyry,  with  seams  of  quartzite  and  hornblendic  volcanic  rock.  ( )n 
Eagle  River,  at  the  base  of  the  section  is  gneiss,  and  above  tin-  i  - 
white  quartzite. 
