170        CONTRIBUTIONS   TO   ECONOMIC   GEOLOGY,   1907,   PART  II. 
Folds— A  small  anticline  in  the  Basin  coal  field  results  in  north- 
easterly dips  for  a  short  distance  in  T.  50  N.,  R.  92  W.  The  coal 
bed  follows  a  devious  S-shaped  course  around  the  anticline  and  the 
adjoining  syncline. 
The  only  other  fold  affecting  workable  coal  beds  is  the  Silvertip 
anticline.  At  Silvertip  the  coal  of  the  Eagle  sandstone  is  exposed 
in  a  broad,  domelike,  unsymmetrical  anticline,  with  dips  of  11°  to 
20°  SW.  on  the  west  limb  and  of  20°  to  45°  NE.  on  the  east  limb. 
As  shown  by  the  geologic  map  (PI.  X),  the  nonworkable  parts  of 
the  coal  beds  are  involved  in  a  number  of  small  anticlinal  and  syn- 
clinal folds  near  Garland  and  Lovell,  Wyo. 
Faults. — Small  dip  faults,  trending  nearly  at  right  angles  to  the 
strike,  occur  in  all  parts  of  the  field.  They  are  especially  common 
on  the  anticlines.  As  a  rule,  these  faults  will  not  interfere  with  min- 
ing, except  in  the  Silvertip  anticline,  on  the  east  side  of  which  some 
of  them  are  so  closely  spaced  as  to  prevent  the  development  of  side 
workings  more  than  2,000  feet  from  the  main  entries.  Along  a  large 
isolated  fault  4  miles  north  of  Bridger,  Mont.,  the  outcrop  of  the 
Bridger  coal  bed  is  offset  nearly  2  miles.  A  smaller  isolated  fault 
encountered  in  the  Rogers  &  Gapin  mine,  near  Manderson,  Wyo., 
probably  offsets  the  outcrop  of  the  coal  bed  to  the  Converse  prospect, 
on  the  bank  of  No  Wood  Creek.  Depressed  fault  blocks,  with  their 
longer  axis  across  the  strike  and  widening  in  the  direction  of  the  dip, 
are  characteristic  features  of  the  structure.  The  Hopkins  and  Sar- 
ver  coal  mines  are  located  near  the  southern  and  northern  limits, 
respectively,  of  one  of  these  depressed  fault  blocks.  The  north  bound- 
ary fault  of  this  block  offsets  the  outcrop  of  the  coal  bed  over  three- 
fourths  of  a  mile;  the  south  boundary  offsets  the  outcrop  over 
one-fourth  of  a  mile.  There  is  a  similar  depressed  fault  block  6 
miles  south  of  Bridger,  Mont.,  in  which  the  Bridger  coal  bed  is  offset 
three-fourths  of  a  mile  to  the  east.     (See  map,  PI.  X.) 
DISTRIBUTION   OF  COAL. 
Coal  occurs  in  the  Cloverly,  Eagle,  Claggett,  Laramie,  and  Fort 
Union  formations.  The  coal  of  the  Cloverly  is  not  workable  within 
the  borders  of  the  area  mapped,  but  Fisher  reports  that  a  coal  bed 
from  which  coal  has  been  mined  for  domestic  use  on  neighboring 
farms  occurs  near  the  base  of  this  formation  in  the  vicinity  of  Bonanza, 
about  25  miles  southeast  of  Basin,  Wyo. 
The  Claggett  formation  contains  several  thin  beds,  none  of  which 
is  of  economic  importance.  On  Dry  Creek,  west  of  Grey  Bull,  Wyo. 
(see  p.  172),  an  opening  has  been  made  on  a  Claggett  coal  bed,  which 
is  not  workable.  The  best  exposure  of  Claggett  coal  is  on  the  south 
bank  "of  Shoshone  River,  near  Byron  (see  p.  181),  where  there  is  21 
inches  of  coal. 
