812  PBE-CAMBBIAN    GEOLOGY   OF    NOBTH    AMEBIC  A. 
along  Cripple  Creek  in  the  vicinity  of  Mound.  Another  granite, 
called  the  Spring  Creek  granitic  mass,  is  of  comparatively  small 
superficial  extent,  and  its  age  with  reference  to  the  other  granites  is 
unknown.     All  are  pre- Cambrian. 
In  the  northwestern  part  of  the  district  there  has  been  found  and 
mapped  an  area  of  a  rock  which  is  mainly  an  olivine  syenite,  though 
the  mass  exhibits  remarkable  range  and  variability  in  mineralogical 
composition.  The  olivine  syenite  is  younger  than  the  Pikes  Peak 
granite,  but  is  pre-Tertiaiy,  for  numerous  diabase  dikes  genetically 
related  to  the  syenite  are  covered  or  intruded  by  Tertiary  eruptive 
rocks.  A  dike  of  anorthosite  cuts  the  olivine  syenite  and  is  genetic- 
ally related  to  it  in  a  manner  similar  to  pegmatite  dikes  in  granite. 
The  schist,  gneiss,  Spring  Creek  granite,  Cripple  Creek  granite, 
and  olivine  syenite  together  constitute  a  wedge-shaped  area  project- 
ing into  the  Pikes  Peak  granite  from  the  west.  The  center  of  vol- 
canic disturbance  is  near  the  point  of  this  wedge. 
WET   AND    SANGRE    DE    CRISTO    MOUNTAINS. 
Schiel,55  in  1855,  describes  the  predominating  rocks  of  the  Sangre 
de  Cristo  Valley  as  a  feldspathic  granite,  passing  gradually  into  a 
gneiss  on  the  right  bank  of  the  creek,  the  gneiss  supporting  a  hard, 
shaly  sandstone  and  a  bluish  brittle  limestone. 
Endlich,64  in  18747  describes  the  region  south  of  the  Arkansas  as 
consisting  chiefly  of  granite.  That  forming  the  Sangre  de  Cristo 
Mountains  differs  in  character  and  appearance  from  that  of  the 
Front  Range.  The  Wet  Mountains  are  regarded  as  eruptive. 
Gneiss  occurs  in  this  range  at  Hunts  Peak  and  from  there  6  or  7  miles 
to  the  northwest,  and  is  regarded  as  metamorphic,  although  it  weath- 
ers more  like  granite  than  a  stratified  rock.  From  the  granite  axis 
of  the  Sangre  de  Cristo  the  sedimentary  rocks  dip  away  both  to  the 
east  and  to  the  west.  The  eruptive  granite  of  the  Sangre  de  Cristo 
is  the  youngest  of  the  region.  Although  the  Sangre  de  Cristo  Range 
is  spoken  of  as  eruptive,  this  is  not  considered  to  be  so  in  the  same 
sense  that  basalt  is  eruptive,  but  to  imply  that  the  granite  by  some 
vertically  acting  force  has  been  thrown  upward  and  may  now  be  in 
contact  with  strata  which  were  once  above  it. 
Cope,™  in  1875,  states  that  in  the  Sangre  de  Cristo  Mountains  is 
stratified  granite,  which  is  either  heavily  bedded  feldspathic  por- 
phyry or  finely  bedded  hornblende  gneiss. 
Endltch,80  in  1877,  states  that  metamorphics  compose  the  main 
bulk  of  the  interior  portion  of  the  lower  Sangre  de  Cristo  Range, 
though  at  many  places  sedimentary  beds  and  volcanic  flows  have 
obscured  the  relations.  The  highest  peaks  of  the  range  are  as  a  rule 
metamorphics,  among  which  granites  and  gneisses  are  predominant. 
