578  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         r bull.  260. 
erings  of  the  basin  are  of  recent  age,  being  now  in  process  of 
formation.  A  considerable  part  of  the  basin  deposits  doubtless  is 
Pleistocene,  but  whether  some  of  the  basal  material  is  of  Tertiary 
age  is  unkown. 
SALT. 
The  presence  of  salt  in  the  Salt  basin  has  long  been  known  to  Mexi- 
cans, who,  in  the  early  days  of  the  occupation  of  the  country,  are  said 
to  have  traveled  for  it  from  distant  parts  of  Chihuahua.  The  first 
wagon  road  to  the  deposit,  hoAvever,  was  not  built  until  1863.  Noti 
long  after  its  construction  the  salt  was  "  located  "  and  claimed,  andi 
an  effort  was  made  to  collect  a  charge  for  the  salt,  which  formerly 
was  free  to  all.  This  provoked  trouble,  which  was  made  an  issue  in  a^ 
personal  fued  between  two  politicians,  and  finally,  in  1877,  resulted 
in  riot  and  bloodshed  at  San  Elizario.  Quiet  was  restored  only  by 
the  intervention  of  the  United  States  Army.0 
This  deposit  of  salt  is  situated  on  the  west  side  of  the  Salt  basin,, 
about  15  miles  southwest  of  El  Capitan  Peak  and  a  little  more  thani 
50  miles  north  of  Vanhorn.  The  deposit  is  locally  known  as  the  saltt 
lake.  It  occupies  a  slight  depression,  and  is  one  of  several  so-calledl 
lakes  similarly  situated  in  this  part  of  the  Salt  basin. 
Unconsolidated,  earthy  gypsum  forms  the  floor  of  most  of  these'' 
lakes  and  surrounds  and  connects  them.    Borax  and  potash  have  beem 
found  in  one  of  the  dry  lakes.     Strontium  occurs  in  the  gypsum  thajj 
surrounds  the  Salt  lake,  and  there  are  traces  of  lithium  in  the  deposits, . 
Outside  the  area  occupied  by  these  depressions  the  materials  of  the 
Salt  basin  generally  are  clay  and  fine  sand,  and  toward  the  margir 
the  surface  is  strewn  with  coarser  debris  from  the  contiguous  high- 
lands. 
Although  some  salt  occurs  in  a  few  of  the  other  "  lakes,"  only  oik 
is  known  to  contain  it  in  important  quantities.  This  is  roughly  ellip 
deal  in  outline  and  has  an  area  of  about  45  acres.  Viewed  from  i 
distance  it  presents  the  appearance  of  a  pond  covered  with  ice  oi 
snow,  so  white  is  the  layer  of  salt  on  its  surface. 
During  the  dusty,  dry  season  the  salt  becomes  impure,  but  after  i 
rain,  and  especially  in  localities  where  the  surface  salt  has  been  latej 
removed,  beautiful  hopper-shaped  crystals  are  formed.  An  analysj 
of  some  of  these,  hy  S.  H.  Worrell,  of  the  University  of  Texas  Minera 
Survey,  gave  the  following  results  : 
°  House  Ex.  Doc.  No.  93,  45th  Cong.,  2d  sess.,  El  Paso  Troubles  in  Texas,  1878. 
