286  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
and  Grass  creeks.  The  dip  of  the  rocks  is  toward  the  northwest  and  the  outcroppii  2 
edges  of  these  sandstones  make  precipitous  southeastward-facing  cliffs.  The  lowest  san  - 
stone,  No.  1  of  the  section,  is  less  prominent  in  its  topographic  effects  than  the  others,  y  t 
is  a  distinct  marker  for  the  position  of  the  most  valuable  coal  bed  in  the  field,  which  li  3 
immediately  beneath  it. 
STRATIGRAPHY. 
The  rock  formations  consist  of  shale,  sandstone,  and  conglomerate,  with  occasion  1 
strata  of  limestone  and  three  or  more  beds  of  coal.  The  numerous  faults  that  intersect  tl  J 
rocks  and  the  spaces  of  concealed  strata  in  the  valleys  prevent  the  measurement  of  a  i 
accurate  section  in  the  vicinity  of  Coalville  except  by  a  detailed  survey  and  a  careful  stud  • 
of  the  fossils.  Little  note  was  taken  of  the  rocks  below  the  lowest  known  workable  co  1 
now  being  developed  at  the  Wasatch  mine, 2  miles  northeast  of  Coalville.  Stanton,  wh  i 
has  studied  the  seel  ion  at  Coalville,  reports  a  that  below  this  coal  are  500  to  600  feet  *  :jj 
interstratified  shale  and  sandstone.  The  following  general  estimated  section,  based  in  pai  , 
on  Stanton's  measurements,  in  ascending  order,  will  give  some  idea  of  the  lithologic  sucoeMf 
sion  and  positions  of  the  coal  beds: 
General  sect  ion  of  coal-hearing  rocks  in  Weber  River  field. 
Feet. 
1.  Wasatch  coal,  being  mined  .-it  Wasatch  and  Grass  Valley  mines 9-  ] 
2.  Sandstone,  thick-bedded,  light  gray 
This  sandstone  is  t  tie  roof  of  coal  in  Wasatch  and  Grass  Valley  mines. 
S.  Blue-clay  marl  (Grass  Valley) 400-' 
Crops  in  valleys  chiefly  and  is  usually  only  partially  exposed.  Coal  occurs  in  the  upper 
part  or  probably  at  t he  top  of  this  shale,  it  is  reported  by  Mr.  Samuel  Clark,  superin- 
tendent of  t  he  Wasatch  mine,  to  be  a  double  seam,  each  bench  being  .'i  to  1  feet  and  sepa- 
rated by  2  to  3  feet  of  9hale.    The  upper  coal  is  succeeded  by  sandstone. 
■l.  Sandstone  and  conglomerate 100-3C 
I  D  I  rraSS  Valley  it  appears  thicker  t  ban  at  Coalville   and  is  separated  into  two  mem- 
bers by  shaly  strata. 
5.  Shale  and  thin  sandstone 400-5C  ■ 
A  bed  of  shell  limestone  OCCUrs  iD  upper  part  and  a  thin  bed  of  coal  is  reported  to  occur 
near  the  same  position  in  the  seel  ion.  A  coal  in  the  upper  part  of  this  group  of  strata, 
once  mined  2  miles  soul  bwesl  of  Coalville,  is  reported  by  Mr.  T.  J.  Lewis,  manager  of  the 
Wasatch  mine,  to  consist  of  t  wo  beds,  each  2  to  3  feet  thick,  separated  by  shale  varying  in 
thickness  from  IJ  to  2  feet  ■ 
6.  Massive  light-yellow  sandstone  and  conglomerate ion-30 
Above  these  sandstones  and  conglomerates  there  is  shale,  probably  1,500  feet  thick, 
which  is  in  turn  followed  by  blown  and  gray  sandstone,  with  minor  shale  beds,  1,.'KK)  to 
1,500  feet  thick,  to  the  base  of  the  great  Wasatch  conglomerate  of  presumably  Tertiary 
age. 
STRUCTURE. 
The  coal-hearing  rocks  in  t  he  vicinity  of  Coalville  on  the  north  and  west  are  tilted  towam 
the  northwest  at  angles  varying  generally  between  16°  and  20°.  The  rocks  also  have  beei 
broken  and  disturbed  by  two  systems  of  faults.  One  is  a  system  of  strike  faults  beariffl 
northeast  and  southwest,  almost  with  the  strike  of  the  rocks.  The  other  is  a  system  o 
dip  faults  at  right  angles  to  the  first.  A  fault  belonging  to  the  first-mentioned  systen 
may  be  seen  northeast  of  Coalville.  It  extends  from  the  northern  boundary  of  the  cit} 
northeastward  across  the  SE.  \  sec.  4  and  the  NW.  \  sec.  3,  T.  2  N.,  R.  5  E.  The  a  ban 
doned  coal  mine  in  the  SE.  \  sec.  4  is  located  near  this  fault.  The  rocks  on  the  southeasl 
side  of  the  fault  have  been  dropped  with  respect  to  those  on  the  opposite  side.  The  massive 
sandstone  in  the  ridge  lying  across  sec.  3  above  and  northwest  of  the  Wasatch  mine  has 
been  thrown  down  until  it  appears  to  extend  800  feet  beneath  its  counterpart  in  the  promi- 
nent ridge  one-half  mile  to  the  northwest,  extending  across  sec.  4.  A  dip  fault  cuts  tfl 
rocks  crossing  near  the  southwest  corner  of  sec.  3.     Another  fault  of  this  system  occurs 
a  Op.  cit. 
