Campbell.]  THE    DEER    CREEK    COAL    FIELD,    ARIZONA.  247 
volcanic  material  as  though  sedimentation  was  at  times  interrupted  lyy 
volcanic  outbursts  and  was  resumed  when  conditions  became  more 
favorable.  The  zone  of  transition  between  sedimentary  and  igneous 
rocks  is  marked  by  a  thick  bed  of  coarse  conglomerate  composed 
largely  of  bowlders  of  granite,  Paleozoic  limestone,  and  quartzite. 
This  is  a  very  characteristic  bed  and  can  be  traced  throughout  the 
Territory,  except  in  the  upper  part  of  the  Deer  Creek  Basin.  Above 
this  bed  of  conglomerate  the  andesite  has  a  great  thickness,  possibly 
reaching  as  much  as  1,000  feet.  In  certain  parts  of  the  field  sedimen- 
tation was  resumed  from  time  to  time,  presumably  between  lava  flows, 
and  consequently  the  lava  is  interstratified  with  sandstone  beds,  and 
in  places  even  small  coal  seams  appear  to  have  been  deposited  in  these 
intervals  of  quiescence. 
GEOLOGIC   STRUCTURE. 
The  structure  of  the  Deer  Creek  coal  field  is  comparatively  simple, 
consisting  of  an  unsymmetrical  synclinal  trough,  the  axis  of  which 
corresponds  approximately  with  the  course  of  Deer  Creek  near  the 
south  side  of  the  basin.  South  of  the  creek  the  rocks  are  sharply 
flexed  and  they  stand  nearly  vertical  along  the  front  of  the  mountain. 
This  great  uplift  terminates  about  3  miles  west  of  Manning's  ranch, 
but  the  disturbance  continues  to  the  west  as  a  small  anticlinal  fold 
crossing  Deer  Creek  near  the  point  where  the  Dudley  vi He  trail  first 
reaches  the  creek.  The  fold  is  of  sufficient  magnitude  to  bring  to  the 
surface  at  this  point  the  bed  of  conglomerate  and  also  some  under- 
lying sandstones. 
The  structure  on  the  north  side  of  the  basin  is  simple;  the  coal- 
bearing  rocks  dip  30°  to  60°  at  the  outcrop  and  then  gradually  decrease 
in  dip  until  in  the  center  of  the  basin  they  lie  approximately  horizon- 
tal. There  have  been  many  minor  disturbances  generally  caused  by 
dikes  which  cut  the  strata  in  all  directions.  The  Upper  field  in  par- 
ticular seems  to  be  disturbed  by  many  minor  structural  features,  the 
soft  rocks  being  folded  in  a  number  of  wrinkles  parallel  with  the  gen- 
eral trend  of  the  syncline;  on  these  small  folds  the  coal  beds  outcrop 
at  many  points. 
In  the  Ash  Creek  Basin  the  structure  is  less  regular,  consisting  for 
the  most  part  of  a  warped,  irregular  floor  with  no  definite  axes  to  the 
depressions.  On  the  whole  it  seems  to  constitute  a  synclinal  basin 
extending  northwest  and  southeast,  but  in  the  latter  direction  it  is 
divided  by  the  great  laccolithic  uplift  on  Ash  Creek  into  two  shallow 
basins.  The  one  lying  between  Ash  Creek  and  Deer  Creek  is  not  well 
exposed,  being  covered  by  recent  lava  flows  so  as  to  obscure  its  struc- 
tural features.  The  one  west  of  Ash  Creek  is  marked  by  Saddle 
Mountain,  which  occurs  in  the  center  of  the  depression,  but  farther 
southwest  the  synclinal  lifts  and  only  a  little  of  the  andesite  and  coal- 
bearing  rocks  now  overlies  the  Carboniferous  limestone. 
