﻿102 
  C. 
  L. 
  Baker 
  — 
  Contributions 
  to 
  the 
  

  

  Front 
  Range 
  of 
  the 
  Sangre 
  de 
  Cristo, 
  the 
  south 
  flank 
  of 
  

   which 
  syncline 
  lies 
  in 
  a 
  high 
  Dakota-capped 
  mesa 
  escarp- 
  

   ment 
  extending 
  east-west 
  for 
  40 
  miles 
  a 
  short 
  distance 
  

   south 
  of 
  Las 
  Vegas. 
  Some 
  low 
  folds 
  of 
  small 
  extent 
  lie 
  

   west 
  of 
  the 
  Pecos 
  River 
  and 
  east 
  of 
  the 
  Sacramento 
  and 
  

   Guadalupe 
  mountains. 
  On 
  the 
  whole, 
  the 
  Permian, 
  Tri- 
  

   assic, 
  Cretaceous 
  and 
  Cenozoic 
  deposits 
  of 
  the 
  Great 
  

   Plains 
  have 
  generally 
  a 
  gentle 
  eastward 
  dip. 
  Sink-holes, 
  

   of 
  the 
  same 
  origin 
  as 
  those 
  of 
  the 
  small 
  basins 
  of 
  central 
  

   New 
  Mexico, 
  are 
  abundantly 
  scattered 
  over 
  the 
  plains 
  

   surface. 
  In 
  the 
  great 
  syncline 
  at 
  the 
  north 
  they 
  are 
  

   found 
  also 
  in 
  the 
  Benton 
  Cretaceous, 
  but 
  may 
  have 
  been 
  

   formed 
  through 
  solution 
  of 
  underlying 
  lower 
  Permian 
  

   salt 
  and 
  gypsum. 
  

  

  Igneous 
  and 
  metamorphic 
  rocks 
  make 
  up 
  the 
  cores 
  of 
  

   the 
  mountain 
  ranges. 
  Paleozoic 
  and 
  Mesozoic 
  sedimen- 
  

   tary 
  rocks 
  of 
  relatively 
  few 
  formations 
  occur 
  on 
  a 
  large 
  

   scale 
  and 
  cover 
  most 
  of 
  the 
  area 
  ; 
  post-Cretaceous 
  igneous 
  

   rocks 
  of 
  acidic 
  types, 
  mainly 
  intrusive 
  but 
  in 
  small 
  part 
  

   volcanic, 
  outcrop 
  in 
  many 
  localities 
  in 
  east-central, 
  cen- 
  

   tral-northern, 
  and 
  central-southern 
  New 
  Mexico; 
  and 
  

   unconsolidated 
  deposits 
  of 
  the 
  later 
  Cenozoic 
  cover 
  inter- 
  

   montane 
  and 
  solution 
  basins, 
  long 
  piedmont 
  alluvial 
  

   slopes, 
  and 
  valley 
  areas. 
  Early 
  Tertiary 
  sediments 
  were 
  

   noted 
  only 
  in 
  the 
  upper 
  Rio 
  Grande 
  Basin. 
  

  

  The 
  oldest 
  rocks 
  of 
  the 
  region 
  form 
  a 
  greatly 
  varied 
  

   complex 
  of 
  metamorphosed 
  sedimentary 
  and 
  igneous 
  

   rocks, 
  cut 
  by 
  large 
  masses 
  of 
  later 
  plutonics. 
  This 
  an- 
  

   cient 
  complex 
  forms 
  the 
  basement 
  rocks 
  of 
  the 
  Sacra- 
  

   mento, 
  San 
  Andreas, 
  Manzano, 
  Sandia, 
  Sangre 
  de 
  Cristo, 
  

   Los 
  Caballos, 
  Fra 
  Cristobal, 
  Oscura, 
  and 
  Los 
  Pinos 
  

   ranges 
  ; 
  the 
  quartzites 
  of 
  the 
  Pedernal 
  Hills 
  and 
  isolated 
  

   knobs 
  of 
  granite 
  west 
  of 
  Pinos 
  Wells 
  and 
  east 
  of 
  Tor- 
  

   rance 
  in 
  central 
  New 
  Mexico 
  are 
  directly 
  overlain 
  by 
  the 
  

   Yeso 
  formation 
  of 
  the 
  early 
  Permian. 
  The 
  younger 
  

   intrusive 
  s 
  of 
  this 
  complex 
  are 
  granites 
  and 
  quartz 
  por- 
  

   phyries 
  in 
  large 
  masses 
  and 
  dikes 
  of 
  pegmatite, 
  aplite, 
  

   quartz 
  and 
  diabase. 
  The 
  older 
  rocks 
  are 
  gneisses, 
  

   schists, 
  quartzites, 
  slates 
  and 
  greenstones. 
  In 
  the 
  

   southern 
  portions 
  of 
  the 
  San 
  Andreas 
  and 
  Sacramento 
  

   mountains 
  they 
  are 
  overlain 
  by 
  upper 
  Cambrian 
  sedi- 
  

   ments; 
  in 
  most 
  of 
  the 
  region 
  they 
  are 
  overlain 
  directly 
  

   by 
  the 
  Magdalena 
  group 
  of 
  the 
  Pennsylvanian. 
  In 
  the 
  

   low 
  isolated 
  hills 
  of 
  central 
  New 
  Mexico, 
  the 
  Yeso 
  forma- 
  

  

  