Campbell]  THE    DEER    CREEK    COAL    FIELD,    ARIZONA.  243 
GENERAL    GEOLOGY. 
Pre- Cambrian  schist. — The  oldest  rocks  found  within  the  territory 
examined  are  schists,  which  occur  on  Ash  Creek  above  the  limestone 
box  canyon  and  on  Gila  River  below  the  mouth  of  Ash  Creek.  No 
fossils  have  been  found  in  these  schists,  consequently  their  age  has 
not  been  determined  definitely,  but  undoubted  middle  Cambrian 
quartzites  and  conglomerates  rest  uncomformably  on  them,  and  for 
that  reason  they  are  regarded  as  being  of  pre-Cambrian  age.  Pro- 
visionally, these  schists  are  correlated  with  those  described  by  Ransome 
from  the  Globe  district  to  the  north,  and  also  from  the  Bisbee  region 
to  the  south,  and  by  Lindgren  from  the  Clifton-Morenci  region  to 
the  northeast.  In  the  Deer  Creek  Basin  the  schists  were  seen  at  one 
point  only,  but  it  seems  probable  that  they  show  in  most  of  the 
anticlines  where  the  movement  has  been  sufficient  to  bring  them  to  the 
surface.  Along  the  north  side  of  the  basin  they  were  not  seen  at  the 
head  of  Hawk  Canyon,  but  to  the  west  they  undoubtedly  come  in 
within  this  territory,  since  they  form  the  main  mass  of  the  Pinal 
Range  west  of  the  river. 
Cambrian  sandstone  and  shale. — Resting  unconformably  upon  the 
schists  just  described,  and  underlying  the  great  upper  Paleozoic  lime- 
stone, is  a  series  of  shale,  sandstone,  and  conglomerate  from  which 
fossils  were  found  in  the  Ash  Creek  Canyon  that  Walcott  pronounces 
to  be  of  middle  Cambrian  age.  The  sandstone  and  conglomerate  are 
known  locally  as  "  the  quartzite,"  and  they  have  a  total  thickness  of 
about  850  feet.  The  closing  episode  of  the  Cambrian  period  seems 
to  have  been  the  deposition  of  60  to  80  feet  of  very  fine,  green  shale, 
which  on  Ash  Creek  appears  directly  beneath  the  great  limestone 
mass.  Provisionally  this  is  correlated  with  the  green  shale  of  the 
Grand  Canyon  region  which  lies  above  the  Ton  to  sandstone. 
Carboniferous  limestone. — Above  the  green  shale  just  described 
occurs  a  great  mass  of  limestone  which,  in  the  Ash  Creek  section, 
has  a  thickness  of  about  1,300  feet.  The  lower  part  of  this  mass  is 
sparingly  fossiliferous  and  no  collections  were  made  by  which  to 
determine  its  age.  The  upper  part  is  richly  fossiliferous,  and  a  col- 
lection from  the  uppermost  beds  outcropping  in  Ash  Creek  Canyon 
indicates  that  this  part  at  least  is  of  Pennsylvanian  age.  It  is  pos- 
sible that  the  lower  part  of  the  great  limestone  mass  may  belong  to 
the  Devonian  or  even  the  Silurian  system,  but  the  evidence  at  present 
available  would  refer  most,  if  not  all,  to  the  Carboniferous. 
This  great  limestone  mass  is  the  most  conspicuous  geologic  feature 
of  the  Deer  Creek  coal  field,  since  in  almost  all  cases  it  forms  the 
boundary  wall  of  the  basin.  Mescal  Mountain  on  the  north  is  com- 
posed almost  exclusively  of  beds  of  this  limestone,  which,  in  the  cen- 
