814  PRE-CAMBRIAN   GEOLOGY   OF    NORTH   AMERICA. 
Mountains  consists  of  coarse  and  fine  grained  granites  and  gneisses ; 
hornblende,  mica,  and  chlorite  schist,  and  subordinate  masses  of  gar- 
net and  epidote  schist  and  occasional  veinlike  bodies  of  coarse  pegma- 
tite. The  schistose  rocks  are  more  prominent  at  the  southern  extrem- 
ity of  the  mountains  than  elsewhere,  while  the  granite  and  gneissic 
rocks  are  more  prominent  in  the  main  mass  toward  the  culminating 
point.  Their  origin  probably  dates  back  to  the  Archean  period.  No 
further  correlation  is  attempted. 
Van  Hise  and  Leith,85  in  1905,  give  notes  on  the  section  along 
Arkansas  River  below  Salida  and  the  adjacent  parts  of  the  Sangre  de 
Cristo  Mountains.  In  going  up  the  gulches  toward  the  Sangre  de 
Cristo  Range  to  the  south,  bowlders  of  granite,  greenstone,  quartzite, 
and  marble  are  abundantly  seen,  indicating  the  probable  existence  of 
a  pre-Cambrian  series  of  some  variety  and  magnitude  in  this  area. 
One  of  the  gulches  directty  south  of  Salida  was  followed  up  to  the 
Silver  Lead  mine.  Well  up  on  the  slope,  to  the  west  of  the  road, 
quartzite,  apparently  dipping  northeasterly  along  the  slope,  was 
found  in  place.  Massive  diorite  forms  most  of  the  area  south  of  the 
road,  and  many  dikes  are  found  in  the  quartzite.  In  going  south — 
that  is,  up  the  mountain — the  quartzite  changes  from  a  reddish  feld- 
spathic  quartzite  to  a  white  vitreous  one. 
For  further  notes  relating  to  the  section  along  Arkansas  River  see 
pages  815-818. 
PARK    RANGE. 
Marvine,62  in  1874,  describes  the  northern  part  of  the  Park  Range 
as  composed  of  a  very  distinctively  and  evenly  bedded  series  of  schists, 
gneisses,  and  granites,  which  have  a  strike  nearly  with  the  ridge,  and 
a  dip  of  40°  or  50°  S. 
Hague,85  in  1877,  describes  the  Park  Range  as  made  up  of  a  sys- 
tem of  highly  crystalline  rocks  of  Archean  age.  The  later  rocks 
form  a  very  subordinate  part  of  the  uplift,  rising  not  more  than  a 
few  hundred  feet  above  the  plain,  where  they  rest  unconformably 
on  the  older  series.  The  rocks  of  the  Park  Range  resemble  more 
closely  those  of  the  Colorado  Front  Range  than  they  do  the  Medi- 
cine Bow,  and  are  referred  to  the  Laurentian.  The  range  contains 
much  structureless  granite  overlain  by  gneisses  and  schists  similar  to 
the  series  of  the  Colorado  Range,  but  carrying  more  hornblende- 
bearing  beds  in  the  upper  members.  On  the  other  hand,  there  are 
not  wanting  rocks  which  are  characteristic  of  the  Medicine  Bow 
series  and  which  were  referred  to  the  Huronian  formation.  The 
range  has  a  monoclinal  structure,  with  the  prevailing  dips  to  the 
west,  while  an  outlying  spur  to  the  east  indicates  the  existence  of  the 
eastern  side  of  the  fold. 
