388  CONTKIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  [bull. 225. 
the  south,  then  turning  back  to  the  north  for  3  miles  or  more,  then 
turning  sharply  around  once  more  to  the  south  along  the  course  first 
described. 
Structure  in  the  immediate  vicinity  of  the  wells. — Such  an  anti- 
clinal fold  must  die  out  gradually  at  the  end.  If  the  axis  be  traced 
southward,  the  dip  of  the  western  limb  should  be  found  less  and  less 
steep.  At  a  certain  point  the  westward  dip  will  become  zero;  there 
will  be  a  structural  bench,  as  it  were,  interrupting  the  general  east- 
ward  dip.  This  bench  will  be  horizontal,  except  for  a  southward 
inclination.  Still  farther  south  the  whole  will  again  dip  toward  the 
cast,  but  in  line  with  the  axis  of  the  anticline  the  dip  will  be  smaller 
than  will  be  found  either  east  or  west  of  that  line. 
In  the  north  side  of  sec.  9,  T.  IN.,  northwest  of  the  Sixmile  reser- 
voir, the  only  dip  is  one  to  the  south.  This  is  on  the  axis  of  the 
larger  fold.  At  this  place  the  axes  of  the  two  folds  are  in  close 
proximity,  and  the  effect  of  the  eastern  and  stronger  fold  is  to  uplift 
the  east  side  of  the  feebler  western  fold,  thus  making  a  horizontal 
bench  out  of  what  would  otherwise  be  only  a  partial  flattening  of  the 
general  eastward  dip.  The  result  is  seen  on  a  line  passing  south 
through  sees.  8, 17,  and  20,  along  which  the  shales  have  no  eastward  dip. 
This  belt  is,  however,  narrow,  a  small  fraction  of  a  mile,  and  in  short 
distances,  both  east  and  west  of  it,  decided  eastward  dips  appear. 
It  is  immediately  east  of  this  bench,  perhaps  on  an  average  one-fourth 
of  a  mile,  that  the  producing  wells  are  found.  The  linear  distribution 
of  the  productive  territory  is  more  pronounced  than  might  be  inferred 
from  the  accompanying  sketch  map.  Speaking  generally,  the  wells 
farthest  from  the  middle  of  this  narrow  belt  have  produced  compara- 
tively little.  The  continuity  of  the  line  becomes  more  striking  if  it  be 
extended  south  to  include  the  Buffalo  gas  well  in  the  southeast  corner  | 
of  sec.  29.  This  position  of  the  oil-producing  strip  is  in  exact  accord 
with  that  of  the  Ohio  oils,  whose  conditions  of  occurrence  have  been 
made  so  well  known  by  the  very  complete  discussion  of  Orton.  a  The 
possible  finding  of  other  pools  remote  from  such  a  structure  need  not 
be  discussed  here.  It  can  only  be  said  that  the  example  of  this  field 
offers  no  warrant  for  prospecting  where  these  structural  features  are 
absent. 
It  may  be  safely  assumed  that  the  one  essential  element  in  the  struc- 
ture above  described  is  the  decided  arrest  of  the  general  eastward  dip. 
The  peculiar  relations  of  two  folds,  whose  effects  at  this  place  unite 
to  produce  the  result,  are  not  believed  to  be  necessary  features  which 
must  be  duplicated  in  the  case  of  any  new  deposits  to  be  discovered. 
Further,  ic  must  not  be  assumed  that  this  or  any  similar  flexure  will 
necessarily  be  oil  bearing  throughout  its  whole  length.  Even  very 
small  transverse  folds  affecting  the  axis  are  sufficient  to  break  up  the 
"The  Tr<  Qton  Limestone  as  a  source  of  petroleum  and  inflammable  gas:  Eighth  Ann.  Rept.  U.  S. 
iirvey,  pt.  2,  1889. 
