SALT,  GYPSUM,  BORAX,  AND  SODA. 
The  mineral  products  grouped  under  the  above  heading,  though 
applied  to  widely  different  uses,  form  a  somewhat  natural  group  so 
far  as  origin  is  concerned.  Their  close  connection  becomes  obvious 
when  their  study  in  the  held  is  attempted,  for  two  or  more  of  these 
salts  will  often  be  found  in  adjacent  and  closely  related  deposits.  This 
is  due  to  the  mode  of  origin  of  such  deposits.  The  materials  here 
grouped  include  certain  sulphates,  chlorides,  carbonates,  or  borates  of 
lime,  magnesium,  sodium,  or  potassium;  and  deposits  of  commercial 
value  are  due  in  almost  every  case  to  the  deposition  of  these  salts,  by 
evaporation,  from  the  sea  or  lake  water  in  which  they  were  contained 
in  solution. 
The  most  important  and  fortunately  the  most  widely  diffused  of 
these  materials  is  common  salt,  whose  uses,  both  in  the  preparation  and 
preservation  of  food  and  in  the  chemical  industries,  are  rapidly  increas- 
ing. For  a  report  on  field  work  by  the  Survey,  during  1903,  on  the 
Utah  and  California  salt  industry,  see  pages  488-495.  Appended  to 
this  report  are  tables  of  analyses  of  rock  salts,  brines,  and  commercial 
salts  from  various  United  States  and  foreign  localities.  Several  of 
the  important  districts  were  examined  during  1903,  while  the  remain- 
ing districts  will  be  visited  in  1904.  A  survey  bulletin  on  the  saline 
deposits  of  the  United  States  will  then  be  published. 
The  next  in  importance  of  these  materials  is  gypsum.  In  addition 
to  the  report  on  Utah  gypsum,  presented  in  this  bulletin,  all  the  com- 
mercially important  gypsum  deposits  of  the  United  States  are  described 
in  Bulletin  No.  223,  of  the  United  States  Geological  Survey,  now  in 
press. 
A  report  on  the  California  borax  deposits  has  recently  been  issued 
by  the  Survey.     This,  together  with  other  Survey  publications  on  the 
materials  of  this  group,  will  be  found  listed  on  page  496. 
482 
