262  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1906,   PART    I. 
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sou  level,  their  summits  lying  3,000  feet  above  the  lowland  area  thai 
extends  westward  from  the  base  of  the  mountains.  The  main  moun- 
tain mass  is  made  up  of  pre-Carboniferous  (p re-Cambrian?)  granites,] 
schists,  and  gneisses,  which  are  overlain  in  patches  by  Carboniferous 
limestone  and  sandstone  and  Permo-Carboniferous  rocks  and  flanked 
on  all  sides  by  Mesozoic  strata.  The  Mesozoic  rocks  are  tilted  at  al 
high  angle  along  the  western  front  of  the  range,  dipping  steeply  west- 
ward away  from  the  mountain  mass  except  where  locally  overturned. 
The  gypsum  deposits  along  the  western  base  of  the  range  lie  near 
the  top  of  the  "Red  Beds7'  series.  They  are  apparently  at  all  place! 
underlain  by  a  bed  of  bright  yellow,  poorly  consolidated  sand,  and  are 
overlain  by  dark  shales  and  yellowish  brown  sandstone  of  Dakota  on 
Jurassic  age,  from  which  they  are  occasionally  separated  by  a  thin 
bed  of  limestone.  The  Mesozoic  rocks  are  tilted  generally  westward 
throughout  the  length  of  the  mountain  range,  but  at  its  extremities] 
at  the  northern  and  southern  ends  of  the  gypsum  outcrop,  as  mapped! 
the  strike  of  the  beds  changes  to  a  northeast-southwest  direction  and 
the  dip  becomes  northwesterly  and  less  steep.  A  fault,  whose  extent 
and  relations  are  not  yet  clearly  understood,  trends  north-south 
between  the  vicinity  of  Cuba  and  a  point  east  of  the  southern  end  of 
the  Nacimiento  Range.  Thisfauli  appears  to  involve  only  the  Creta- 
ceous rocks  overlying  the  Dakota  formation. 
GYPSUM   DEPOSITS. 
During  the  hast  v  examination  of  the  deposits  time  was  not  available 
to  measure  sections  in  the  pre-Cretaceous  rocks  except  at  great  inter- 
vals along  the  outcrop,  and  the  measurements  made  were  not  all 
accurate.  At  ( rallina,  on  Gallina  Creek,  near  the  northern  limit  of  the 
gypsum  outcrop  as  here  mapped,  a  bed  of  massive  white  gypsum 
outcrops  within  the  limits  of  the  village,  where  it  has  been,  to  a  very 
limited  extent,  quarried  and  burned,  the  product  being  used  by  the 
inhabitants  for  plastering  their  adobe  houses.  The  deposit  is  readily 
accessible  and  is  mined  by  open  cut.  The  gypsum  bed  may  be  traced 
eastward  from  Gallina  for  many  miles,  as  it  outcrops  along  Gallina 
Creek  in  the  southward-facing  bluff  of  Mesa  Blanca  Capulin.  The 
rocks  in  this  mesa  lie  almost  flat,  having  a  very  low  northwesterly  dip, 
about  equal  in  grade  to  the  fall  of  the  creek.  A  section  of  the  lower 
Mesozoic  rocks  containing  the  gypsum  deposits  is  given  below. 
Section  of  rocks  in  Mesa  Blanca  (lapulin. 
Feet. 
Dakota  red  sandstone 80 
Red  and  green  shale  (Dakota  or  Jurassic  i 300 
Gypsum 40  + 
Yellow,  poorly  consolidated  sand 50 
Red  sandstone  (Jurassic-Triassic  > 300-1- 
