290  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
Valley  and  of  the  lower  slopes  of  the  escarpments  at  its  borders  is  a  friable  blue-clay  marl. 
The  larger  streams  that  flow  from  the  plateaus  have  worn  through  the  bowlder  layer, 
forming  flat  box  valleys  in  the  soft  clay  marl.  The  smaller  drainage  channels  on  cutting 
through  the  bowlder  and  gravel  surface  sink  deeply  into  the  marl,  producing  an  extremely 
rough,  bowlder-strewn,  badlands  type  of  topography.  Before  this  erosion  occurred  the 
old  valley  floor  stood  high  above  its  present  level  and  was  covered  with  a  thick  mantle 
of  bowlders  and  gravel,  which  was  spread  over  the  plain  for  several  miles  from  the 
escarpments. 
Beds  of  sandstone  that  are  locally  variable  in  thickness  occur  in  the  shale  of  Castle  Valley 
500  to  700  feet  below  the  top  of  the  formation.  At  the  base  of  the  Book  Cliffs  they  are 
thin  and  shaly  and  have  little  effect  on  the  topography.  From  Price  River  westward 
they  increase  in  thickness  rapidly,  aggregating  more  than  100  feet  on  Gordon  (-reek. 
Toward  the  south  they  thin  to  mere  bands  on  reaching  Huntington  Valley;  but  still  farther 
south  they  become  thicker,  reaching  200  to  250  feet  on  Muddy  and  [vie  creeks  at  the  south 
end  of  the  coal  field.  These  sandstones,  occurring  as  they  do  in  the  midst  of  soft  shales, 
make  peculiar  and  striking  features  in  the  topography  and  from  them  Castle  Valley  has 
acquired  its  name.  Box  canyons,  many  of  them  impassable,  fluted  and  terraced  cliffs, 
castellated  headlands,  ami  perpendicular  towers  mark  their  occurrence.  Even  where  the 
sandstone  is  thin  it  serves  as  a  protecting  cap  to  the  buttes,  and  in  many  places  the  under- 
lying clay  marl  stands  in  perpendicular  columnar  walls  KM)  feet  or  more  in  height .  The 
soft  layers  in  the  mail  weather  out  in  parallel  bands  in  the  cliffs,  leaving  the  hard  layers 
as  projecting  ledges.     Thus  the  cliffs  simulate  rows  of  gigantic  books. 
There  is  a  gradual  rise  of  the  surface  from  Castle  Valley  toward  the  San  Rafael  Swell. 
The  rocks  beneath  the  Castle  Valley  marl  consist  of  pinkish  sandstone  several  hundred 
feet  thick.  This  sandston<  make-,  the  Red  Plateau  and  the  western  rim  of  the  Swell.  In 
turn,  it  is  underlain  by  friable  arenaceous  shale.  On  cutting  through  the  sandstone  the 
streams  have  descended  rapidly  in  the  soft  underlying  marl,  creating  a  strikingly  rugged 
and  almost  impassable  country,  which  extends  diagonally  across  Emery  County  from  the 
Red  Plateau  toward  the  southwest.  The  main  escarpment  produced  by  these  sandstones 
faces  east  and  south  toward  the  center  of  the  Swell.  Numerous  channels  draining  into 
San  Rafael  River  and  Muddy  Creek  have  cut  by  headwater  sapping  into  this  escarpment, 
reproducing  in  a  measure  the  topography  of  the  Book  Cliffs  and  the  Wasatch  Plateau 
escarpments,  with  even  more  picturesque  effect.  Perpendicular  dill's  mark  the  escarp- 
ment faces  and  deep  box  canyons  extend  back  into  the  plateau.  On  the  divides  and 
projecting  points  between  the  drainage  lines  near  the  escarpments  there  are  high  pinnacles 
and  rugged  towers  of  pinkish  sandstone. 
STRATIGRAPHY. 
The  survey  of  the  Book  Cliffs  field  during  the  past  season  had  special  reference  only  to 
the  occurrence  of  coal.  Such  work  as  could  be  devoted  to  formations  contiguous  to  the 
coal-bearing  rocks  was  in  the  nature  of  a  reconnaissance. 
The  rocks  are  naturally  arranged  in  thick  groups  of  strata.  In  each  group  either  sand- 
stone or  shale  greatly  predominates.  They  contain  scant  fossil  remains,  and  sufficient  infor- 
mat  ion  regarding  t  heir  age  has  not  been  obtained  to  correlate  them  with  similar  well-known 
beds  in  other  parts  of  the  country.  The  entire  section  is  without  doubt  Cretaceous, and  the 
principal  coal-bearing  strata  are  within  the  Laramie  formation.  Further  study  of  the  sec- 
tion and  detailed  areal  mapping  will  doubtless  show-  that  the  principal  groups  of  strata  may 
be  subdivided  into  smaller  units  of  more  uniform  lithologic  character.  For  these  reasons  the 
formations  w  ill  not  be  named,  being  described  by  reference  to  their  occurrence. 
Shale  of  the  San  Rafael  Swell. — The  lowest  formation  was  noted  in  a  reconnaissance  down 
Muddy  Creek  southeast  of  Emery.  Only  the  upper  2,50  to  300  feet  of  the  formation  was 
seen.  It  consists  of  bluish  arenaceous  shale.  From  the  cliffs  of  overlying  sandstone  it  could 
be  seen  that  deposits  of  the  same  character  make  the  desert  12  to  15  miles  out  on  the  western 
slopes  of  the  San  Rafael  Swell. 
