816  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
Endlich,64  in  1874,  states  that  the  granite  of  the  Sa watch  on  the 
west  side  of  the  Arkansas  is  probably  post-Silurian.  This  range  has 
two  kinds  of  granite  that  are  peculiar  to  it  and  an  older  predomina- 
ting one.  Both  of  these  are  newer  than  the  red,  middle,  and  coarse- 
grained rock  found  in  the  Wet  Mountains.  The  first  of  these  varie- 
ties composes  the  main  part  of  the  range  and  constitutes  its  most 
prominent  peak,  Mount  Princeton.  Besides  this,  there  is  protogine 
and  eruptive  granite.  Mount  Ouray  is  composed  in  large  part  of 
hornblende  rock.  On  one  side  the  hornblende  and  granite  are  inter- 
stratified,  the  granite  being  regarded  as  intruded  betAveen  the  strata. 
The  change  from  the  granite  to  the  hornblende  rock  is  always  abrupt. 
Lakes,00  in  1886,  describes  the  Sawatch  Range  as  consisting  of 
gneiss  and  granite  penetrated  by  volcanic  dikes,  with  patches  of 
Silurian,  Carboniferous,  and  more  recent  strata  resting  on  or  uptilted 
against  each  flank.  In  the  Aspen  region  are  two  granites,  one  the 
metamorphic  granite  of  the  Sawatch  and  the  other  a  diorite  and 
eruptive  lava  of  the  Elk  Mountain  system.  On  the  granites  are  un- 
conformably  located  the  Cambrian  strata,  the  base  of  which  is 
quartzite. 
Cross,01  in  1893,  describes  a  series  of  hornblendic,  micaceous,  and 
chloritic  schists  on  the  eastern  side  of  Arkansas  River  near  Salida, 
Colo.  In  places  these  grade  into  massive  rocks.  They  are  cut  by 
granitic  and  pegmatitic  veins,  as  well  as  by  dikes  of  porphyry.  A 
detailed  microscopical  study  leads  to  the  conclusion  that  the  rocks 
are  a  metamorphosed  volcanic  series.  The  whole  constitutes  a  part 
of  a  single  anticline.  The  schists  are  unconformably  below  the  Silu- 
rian, and  as  the  known  Cambrian  in  Colorado  is  a  thin  series  of 
quartzites  and  shales  conformable  with  the  Silurian,  the  Salida 
schists  are  considered  as  pre-Cambrian.  The  relations  of  the  schists 
to  the  Archean  complex  are  not  exposed,  but  they  are  probably  a  con- 
tinuation of  the  hornblende  schists  of  Marshall  Pass.  Greenish 
schists  are  found  at  Tincup  Pass,  and  near  the  town  of  Tincup  are 
a  highly  crystalline  marble  interbedded  with  the  green  schists,  and 
fine-grained  gneissoid  rocks,  showing  that  metamorphosed  sedimen- 
tary rocks  do  exist  among  the  crystalline  schists  of  the  Sawatch 
Range.  Taking  into  account  all  the  facts,  it  is  thought  that  the 
schists  and  massive  rocks  of  the  Salida  section  probably  represent  a 
great  series  of  surface  lavas,  erupted  in  Algonkian  time. 
Eldridge,92  in  1894,  maps  and  describes  the  Crested  Butte  quad- 
rangle, in  the  Elk  Mountains,  Colorado,  and  finds  that  on  the  north- 
east and  southeast  corners  of  the  district  are  Archean  areas.  These 
consist  mainly  of  granite  and  granite  gneiss,  with  local  developments 
of  gneiss  and  schist. 
Lakes,93  in  1897,  sketches  the  geology  of  the  Gunnison  gold  belt,  in 
Gunnison  County,  Colo.,  from  Cebolla  River  on  the  west  to  the  head 
