fenneman.]  BOULDER    OIL    FIELD,   COLORADO.  387 
mentioned  above  as  belonging  to  the  same  flexure  as  the  monocline 
of  the  oil  field.  Thence  the  outcrop  goes  north  by  east  through  the 
west  side  of  sec.  32,  T.  2  N.  For  nearly  a  mile  north  of  this  the 
ridge  is  lost,  but  it  reappears  in  the  west  side  of  sec.  20,  running 
almost  north.  On  the  north  side  of  this  section  the  outcrop  disappears 
under  the  mesa. 
Crossing  Table  Mountain  in  a  northeasterly  direction  the  observer 
comes  to  the  northern  side  of  the  mesa,  at  the  middle  of  sec.  9.  At 
this  point,  emerging  from  the  steep  side  of  the  plateau,  the  sharp 
crags  of  this  same  sandstone  are  seen,  forming  a  bold,  bare  ridge 
running  far  away  to  the  northeast  (N.  27°  E.). 
If  now  the  mantle  rock  were  removed  from  the  mesa  top  the  out- 
cropping sandstone  ledge  would  be  seen  to  describe  a  great  loop, 
instead  of  cutting  straight  across  from  the  point  where  it  disappears 
under  the  southwest  side  to  where  it  reappears  on  the  northeast.  The 
evidence  of  this  will  appear  from  the  following:  As  noted  above,  the 
strike  of  the  lasi  mile  or  two  on  the  south  side  is  nearly  north.  Simi- 
larly on  the  northeast  side  the  ledge,  which  approaches  the  plateau 
with  a  strike  of  S.  27°  W.,  turns  just  before  its  disappearance  to  a 
direction  differing  only  8°  from  due  south.  Either  line  of  outcrop  if 
continued  across  the  mesa  would  miss  the  position  of  the  other  by 
from  1  to  2  miles. 
Southeast  of  Table  Mountain,  one-half  mile  west  of  Haystack  Butte, 
the  stratum  appears  again,  striking  N.  35°  W.,  and  dipping  10°  NE. 
It  forms  a  low  ridge,  ending,  as  in  the  other  cases,  against  the  steep 
mesa  scarp.  This  ledge  is  doubtless  directly  continuous  with  that 
which  abuts  against  the  north  edge  at  the  middle  of  sec.  9. 
The  two  outcrops  which  end  against  the  south  side  of  Table  Moun- 
tain are  more  than  a  mile  apart.  They  represent  the  same  stratum 
which,  if  the  soil  cover  could  be  removed,  would  be  found  outcrop- 
ping again  in  an  intermediate  position,  with  a  dip  toward  the  west. 
This  supposed  middle  outcrop  and  the  eastern  one,  which  is  plainly 
seen,  represent  an  anticline  whose  crest  has  been  eroded  away. 
Wherever  exposures  permit  the  reading  of  dips,  the  latter  are  seen 
to  accord  with  the  structure  above  described.  Although  the  sandstone 
does  not  outcrop  on  the  western  limb  of  the  anticline,  westward  dips 
are  plainly  seen  within  the  shales  at  the  place  where  such  dips  should 
be  expected.  At  the  north  end  of  the  canoe-shaped  synclinal  trough 
southward  dips  are  found,  just  as  expected.  The  more  detailed 
evidence  of  this  echelon  fold  is  reserved  for  the  bulletin  covering 
the  general  geology  of  the  area.  If,  then,  the  continuous  outcrop  of 
the  sandstone  were  laid  bare,  it  would  be  seen  to  cross  Table  Mountain 
with  a  southerly  trend  from  the  middle  of  sec.  9,  pass  in  a  south- 
easterly course  past  Haystack  Butte,  looping  perhaps  a  mile  farther  to 
