818  PRE-CAMBRIAN    GEOLOGY   OF    NORTH    AMERICA. 
pre-Cambrian  quartzite  associated  with  the  volcanics  is  really 
Paleozoic. 
Van  Hise  visited  the  Sedalia  mine,  about  5  miles  north  of  Salida, 
on  Arkansas  River.  It  is  located  in  micaceous  and  quartzose  schists 
cut  by  granite  dikes.  Near  the  dikes  large  porphyritic  garnets  have 
developed  in  some  places,  and  in  other  places  actinolite,  which  may  be 
seen  altering  into  asbestos.  The  schist  is  broken  into  a  massive  brec- 
cia in  the  mine  proper.  Intrusive  diorite  is  also  seen.  In  returning 
to  Salida  along  the  cliffs  he  observed  that  the  dioritic  material  be- 
comes much  more  abundant,  and  is  indeed  more  abundant  than  the 
schists,  although  the  quartzitic  schist  was  found  at  intervals  as  far 
as  the  section  was  followed — that  is,  about  2  miles  southeast  of  the 
mine— where  a  reentrant  carries  the  exposures  back  to  the  east  a  mile 
or  more.  The  diorites  all  seem  massive  and  are  probably  all  intru- 
sive, like  the  diorite  dikes  seen  at  the  mine.  The  dioritic  material 
sometimes  becomes  schistose.  Where  least  metamorphosed  the  schist 
approaches  a  novaculite  in  nature. 
See  further  notes  of  Van  Hise  and  Leith  on  adjacent  parts  of  the 
Sangre  de  Cristo  Mountains,  this  chapter,  page  814. 
GRAND    AND    GUNNISON    RIVERS. 
Schiel,53  in  1855,  states  that  along  Coochetopa  Creek  and  Grand 
River  valleys  are  granite,  gneiss,  shale,  and  mica  slate. 
Peale,63  in  1874,  states  that  adjacent  to  the  Gunnison  a  section  has 
at  its  base  rust-colored  granite,  above  which  is  mica  schist,  and  over 
this  quartzite  and  sandstone. 
Stevenson,65  in  1875,  states  that  at  several  localities  along  the 
Grand  and  Gunnison  is  a  peculiar,  regularly  laminated  gneiss  which 
resembles  a  micaceous  sandstone.  It  always  occurs  directly  under  the 
sedimentary  rocks  and  no  similar  formation  occurs  lower  down.  It  is 
clearly  unconformable  to  the  great  mass  of  schist  and  gneiss,  though 
precisely  like  them  in  its  changes.  In  consideration  of  all  the  circum- 
stances, one  can  not  resist  the  temptation  of  regarding  it  as  belonging 
to  a  later  series. 
Peale,95  in  1876,  describes  Archean  rocks  as  occurring  along  and- 
near  the  gorges  of  Eagle  and  Gunnison  rivers.  The  rocks  of  Eagle 
River  are  known  to  be  pre-Potsdam,  because  at  the  head  of  the  stream 
such  rocks  rest  upon  them.  On  Gunnison  River  the  Archean  rocks 
are  gneisses  and  schists.  The  presence  of  Dakota  beds  here  resting 
upon  the  Archean  is  supposed  to  prove  that  in  pre-Cretaceous  times 
this  area  was  above  sea  level. 
Peale,96  in  1877,  describes  the  Archean  rocks  of  Grand  River. 
These  occur  in  limited  areas  throughout  the  district  between  parallels 
37°  52'  and  39°  15'  and  meridians  107°  and  109°  30'.  They  are 
generally  confined  to  the  courses  of  streams  flowing  in  canyons.     In 
