560 
CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904. 
[BULL.  260. 
ferent  localities  varies  somewhat,  but  in  general  is  quite  uniform. 
The  following  table  gives  several  analyses  of  bentonite,  made  at  the 
Wyoming  State  School  of  Mines. 
Analyses  of  bentonite  from  Wyoming. 
Si02 . _ 
Al203-_ 
Fe203--- 
MgO  . 
Ca6_. 
NaOKO 
S(V- 
H20_. 
Sp.  gr  . 
Peach 
Creek. 
59.  78 
15. 10 
2.40 
4.14 
.73 
16.26 
2.180 
Crook  County. 
61.08 
17.12 
3.17 
1.82 
2.69 
.  20  NaO 
Weston 
County. 
63.25 
17.62 
3.70 
3.70 
4.12 
1.53 
132 
Natrona 
County. 
65. 24 
15.88 
3.12 
5.  34  +  CaO 
9.17 
Uses. — This  clay  has  been  used  in  various  ways,  chiefly  in  the 
manufacture  of  some  of  the  higher  grades  of  soap,  the  clay  giving 
to  the  soap  a  certain  weight  and  body  which  is  considered  desirable. 
It  has  also  been  found  valuable  as  a  packing  for  a  special  kind  of 
horseshoe  and  as  a  diluent  for  certain  powerful  drugs  sold  in  pow- 
dered form.  Small  quantities  are  used  as  an  adulterant  in  making 
candy,  after  the  alkali  associated  with  it  has  been  removed.  In  this 
condition  it  closely  resembles  terra  alba,  which  is  generally  used. 
Owing  to  its  high  absorption,  its  use  in  the  manufacture  of  dynamite 
has  been  suggested.  There  are  also  other  uses  suggested,  such  as  for 
loading  paper  and  for  adulterations  of  various  other  kinds. 
Distribution. — Bentonite  has  been  found  extensively  in  Wyoming. 
It  has  been  reported  from  Crook,  Johnson,  Weston,  Converse,  Na- 
trona, Carbon,  Albany,  Laramie,  and  Bighorn  counties.  The  accom- 
panying map  (fig.  25),  compiled  from  various  sources,  will  show 
approximately  the  location  of  the  larger  areas  of  the  Benton  forma- 
tion in  W}^oming. 
Benton  group. — The  rocks  of  the  Benton  group  are  the  most  wide- 
spread and  constant  in  character  of  all  the  sedimentary  deposits  of 
the  Great  Plains  region.  Throughout  Wyoming,  however,  consid- 
erable variation  is  noted  in  passing  from  east  to  west.  In  northeast 
W}^oming,  on  the  west  flank  of  the  Black  Hills,  the  maximum  thick- 
ness is  reached.  Here  the  group  consists  of  three  members — a  basal 
series  of  dark  shales,  comprising  the  Graneros,  in  which  bentonite 
occurs ;  a  medial  limestone,  known  as  the  "  Greenhorn  limestone,'! 
and  an  upper  shaly  series  with  sandy  layers,  known  as  the  "  Carlile 
