GYPSUM,  PLASTERS,  ETC 
GYPSUM  IN  NORTHWESTERN  NEW  MEXICO. 
I'.\    Mii.i.\i;i>    K.   SlIALER. 
INTRODUCTION. 
The  field  work  on  which  the  following  notes  are  based  was  carried 
on  in  connection  with  a  reconnaissance  survey  of  the  Durango-Gallud 
coal  field  during  the  fall  of  1905. 
Extensive  deposits  of  gypsum  occur  at  many  places  in  New  Mexico, 
particularly  in  the  southeastern  and  northwestern  parts  of  the  Terri- 
tory, "but  they  are  developed  only  at  Audio,  on  the  line  of  the  Rock 
Island  Railroad,  where  a  plaster  mill  has  been  in  operation  for  several 
years.6 
The  gypsum  along  the  western  base  of  the  Sierra  Nacimiento  was 
known  at  leas!  as  early  a-  1849,  when  Simpson0  mentioned  its  occurs 
rence  in  his  journal.  In  1859  New  berry (/  saw  these  deposits  and 
described  them  as  'immense  masses  of  snowy  gypsum."  Copee  in 
1875  also  refers  to  extensive  deposits  of  gypsum  along  the  western 
baseofSierra  Nacimiento.  Coperegarded  these  deposits  as  Jurassic, 
but  Newberry  was  inclined  to  the  belief  that  they  are  of  Triassic  age. 
It  is  highly  probable  t  hat  these  beds  were  formed  by  precipita- 
tion of  salts  from  sea  water  evaporated  in  a  partly  or  entirely  inclosed 
basin.     This  seems  to  have  been  the  opinion  of  Cope,  who  says : ' 
In  the  badland  trad  I  obtained  -at  isfactory  evidence  of  the  lacustrine  character  of 
the  formation,  a  point  of  much  importance,  inasmuch  a.-  the  nature  of  these  beds  has 
remained  very  obscure  up  t<>  the  presenl  time.  The  evidence  consists  of  numerous 
specimens  "i  bones  and  teeth  of  two  or  throe  species  of  saurians,  one  of  which  at  least 
was  of  terrestrial  habits,  according  to  our  presenl  knowledge. 
a  Herrick,  H.  N.,  Gypsum  deposits  in  New  Mexico;  Bull.  U.  S.  Geol.  Survey  No.  223,  pp.  89-99. 
i>  Eckel,  E.  C,  Gypsum  and  gypsum  products  in  1905:  M  ineral  Resources  U.  S.  for  1905,  pp.  1105-1115. 
c  Simpson,  James  EL,  Journal  of  a  military  reconnaissance  from  Santa  Fe,  N.  Mex.,  to  the  Navajo 
count  ry,  pp.  25-26. 
d  Newberry,  J.  S.,  Exploring  expedition  from  Santa  Fe  to  junction  of  Grand  and  Green  rivers,  1859, 
p. 177. 
e  Cope,  E.  D.,  U.  S.  Geog.  Survey  W.  100th  Mer.,  vol.  4,  pp.  1-13. 
/  Loc.cit.,p.9. 
260 
