484  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1903.  [bull. 225. 
and  forms  the  entire  mass  of  a  prominent  spur  at  the  entrance  to  Salt 
(reek  Valley,  and  outcrops  from  the  level  of  the  creek  up  the  slope 
in  a  southeasterly  direction  in  the  form  of  a  vertical  bed  or  lens.  The 
dimensions  of  the  exposed  portions  of  this  body  are  275-300  feet  in 
thickness,  500  feet  in  height  along  the  bedding,  and  at  least  700  feet 
in  length  along  the  strike.  The  length  depends  upon  whether  the 
deposit  thins  out  along  the  strike,  is  faulted,  or  continues  unbroken. 
Owing  to  a  thick  blanket  of  snow,  which  covered  the  upper  portion 
of  the  gypsum  croppings  to  a  depth  of  2i  to  3  feet  at  time  of  visit, 
this  could  not  be  observed.  The  croppings  are  reported,  however,  to 
have  been  traced  southeastward  for  several  hundred  feet  to  the  main 
divide. 
Although  the  entire  thickness  of  the  deposit  is  made  up  of  gypsum, 
the  character  of  the  rock  varies  somewhat  in  different  beds.  This  is 
shown  in  the  following  section  from  foot  to  hanging  wall: 
General  section  of  the  Nephi  gypsum  deposit 
Feet. 
Interbedded  shale  and  gypsum,  marl  and  gypsum  dirt 30 
Rock  gypsum,  ' '  first-class  " 1 65 
Rock  gypsum,  fractured,  occasional  bands  of  disseminated  calcare- 
ous particles,  etc 75 
Rock  gypsum,  "first-class" 55 
Gypsum  and  shale,  transition  to  shale 50 
The  second  member  affords  all  of  the  present  output;  the  third, 
though  gypsum  and  easily  quarried  owning  to  its  fractured  state,  is  not 
quite  so  pure;  while  the  fourth  is  of  excellent  grade,  and  will  probably 
be  excavated  in  conjunction  with  the  second  by  the  open-cat  method 
in  the  near  future. 
The  first-class  rock  is  massive,  dense,  lusterless,  and  light  grayish 
brown  in  color.  The  chief  variations  are  a  mottled,  whiter,  harder 
phase,  which  occurs  at  the  top  of  the  main  bed  exploited,  and 
"shaly"  bands.  The  bands  are  zones  in  which  small  brown  angular 
fragments  are  included  in  white  and  brown  rock  gypsum.  These 
fragments  prove  on  analysis  to  be  more  calcareous  than  the  remainder 
of  the  rock. 
An  analysis  by  Dr.  E.  T.  Allen,  of  the  U.  S.  Geological  Survey,  of 
first-class  gypsum  from  the  second  member,  and  also  an  analysis  of 
shaly  portions  in  waste  rock  from  the  third  member,  afford  valuable 
data.  From  these  analyses  Doctor  Allen  determines  that  the  first  sam- 
ple is  made  up  of  76  per  cent  gypsum,  22.5  per  cent  anhydrite,  and  1.5 
per  cent  calcium  carbonate  (limestone  ?) ;  and  that  the  second  is  com- 
posed of  60.5  per  cent  gypsum,  22  per  cent  anhydrite,  17  per  cent 
calcium  carbonate  (limestone?),  and  0.5  per  cent  magnesium  carbonate 
(dolomite?). 
Perhaps  the  most  important  feature  brought  out  b}^  these  results, 
next  to  showing  a  high  gypsum  content,  is  that  the  first-class  rock,  as 
