THE   CORDILLERAS.  769 
af  which  to  the  Tertiary  are  not  easy  to  make  out.  The  Vermejo 
Mountains  have  a  nucleus  of  massive  metamorphic  rocks. 
Newberry,9  in  1876,  states  that  in  the  Santa  Fe  Mountains  is  found 
coarse  red  granite,  characteristic  of  the  central  portion  of  the  Rocky 
Mountain  system.  The  Carboniferous  strata  rest  directly  upon  the 
granites.  The  central  axis  of  the  Nacimiento  Mountain  is  composed 
of  a.  similar  massive  red  granite,  upon  the  slopes  of  which  rests  the 
Carboniferous  formation,  for  the  most  part  limestone,  in  many  places 
nearly  vertical,  yet  but  slightly  metamorphosed. 
Stevenson,10  in  1879,  describes  a  continuous  Archean  area  on  the 
western  side  of  the  district  running  from  Spanish  Peaks  south.  It 
forms  the  axis  of  the  Culebra  Range,  continues  through  the  Taos  and 
Mora  ranges,  and  passes  into  the  Cimarron  Range.  The  Santa  Fe 
and  United  States  anticlines  show  Archean  rocks  which  are  separated 
from  the  main  area.  The  rocks  show  great  uniformity  in  character, 
including  gneissoid  granite,  gneiss,  and  mica  schist  as  the  predomi- 
nant types. 
Stevenson,11  in  1881,  gives  a  systematic  account  of  the  Archean 
rocks  of  southern  Colorado  and  northern  New  Mexico.  Four  areas 
are  seen  within  the  district.  The  most  western  marks  the  course  of 
the  Santa  Fe  axis;  the  second,  that  of  the  Culebra-Mora  axis,  and 
the  third  and  fourth  that  of  the  Cimarron  axis.  The  rocks  in  the 
Santa  Fe  axis  are  gneiss,  mica  schist,  which  resembles  sandstones,  and 
granite.  South  of  the  Santa  Fe  road  are  numerous  exposures  of  an 
exceedingly  coarse  granite  or  granite  conglomerate.  With  this  are 
many  beds  of  almost  black  gneiss,  holding  beds  of  snow-white  quartz. 
The  Culebra-Mora  axis  varies  in  width  from  5  to  25  miles.  It  in- 
cludes granite,  gneissoid  granite,  micaceous  and  hornblendic  schists, 
and  quartzites.  Compact  gneiss,  quartzite-like  in  character,  is  found 
in  the  main  canyon  of  Costilla  Creek.  Bands  of  quartzites  are  found 
on  Comanche  Creek,  the  north  fork  of  Moreno  Creek,  in  Costilla 
Creek  range  on  Coyote  Creek,  and  in  the  vicinity  of  Santo  Nino  on 
Cebolla  Creek.  These  are  sometimes  found  in  gneissoid  granite  and 
sometimes  in  mica  schist.  The  granite  below  the  junction  of  the 
forks  of  Moreno  Creek  is  very  coarse  and  resembles  conglomerate. 
The  rocks  of  the  Cimarron  axis  include  mica  schist,  coarse  granite. 
and  gneiss  sometimes  resembling  quartzite.  The  dips  of  the  Archean 
rocks  are  much  confused,  and  the  distortion  at  most  localities  is  so 
great  that  neither  the  succession  of  the  strata  nor  the  general  struc- 
ture could  be  made  out  during  the  brief  examinations.  Positive 
proof  of  unconformity  to  the  overlying  Carboniferous  is  not  easily 
obtained,  the  main  obstacle  in  the  way  of  making  the  determination 
being  the  character  of  the  rock.  Usually  the  disturbance  near  the 
junction  of  the  two  series  is  very  violent,  and  the  rah'  of  dip  changes 
greatly  within  a  short   distance,  sometimes  becoming  even  reversed. 
55721— Bull.  360—09 49 
