van  hise.]  THE    CORDILLERAS.  329 
sandstone  at  the  mouth  of  Grand  canyon,  at  Music  mountain,  and  in 
the  canyon  of  New  river.  At  Truxton  and  on  the  road  to  the  south- 
westward  granite  occurs  in  the  hills,  often  lava-capped ;  is  found  at  Cross 
mountain,  near  fort  Rock;  at  Aztec  pass;  at  Juniper  mountains;  be- 
tween Prescott  and  Agua  Fria  valley,  and  in  the  Black  hills.  In  the 
Juniper  mountains  there  are  also  found  highly  lnetamorphic  rocks,  as 
schists,  slates,  etc.,  often  covering  considerable  areas  and  with  which 
many  of  the  silver  and  gold  bearing  lodes  of  the  country  are  associated. 
At  camp  Verde  on  the  river  Verde  sedimentary  rocks  rest  upon  syen- 
ites. The  Ton  to  sandstone  rests  upon  the  granite  in  the  Sierra  Ancha, 
in  the  San  Carlos  valley,  and  in  the  Apache  mountains.  The  main 
mass  of  the  Pinal  mountains  is  granite,  but  upon  their  northeast  flanks 
is  a  long  area  of  highly  metamorphic  rocks,  consisting  mostly  of  crys- 
talline schists,  micaceous,  chloritic  and  talcose,  their  erosion  forming 
an  intricate  maze  of  small  valleys,  separated  by  sharp  ridges,  which 
present  a  strong  contrast  with  the  more  massive  features  of  the  moun- 
tains. The  granites  and  schists  of  Pinal  mountains  extend  along  Pinal 
creek  to  camp  Pinal. 
Powell,29  in  1876,  further  describes  as  unconformably  below  the 
Tonto  sandstone  the  Grand  canyon  sandstones,  shales  and  limestones, 
10,000  feet  in  thickness ;  and  below  this  the  Grand  canyon  schists,  of  un- 
determined thickness,  composed  of  hornblendic  and  micaceous  schists 
and  slates,  associated  with  beds  and  dikes  of  granite.  The  Grand 
canyon  group  rests  unconformably  upon  the  crystalline  schists.  The 
evidence  of  this  is  complete,  for  the  lower  sandstones  and  conglomer- 
ates first  filled  the  valleys  and  then  buried  the  hills  of  schistic  rocks, 
and  these  conglomerates  at  the  base  of  the  group  are  composed  of 
materials  derived  from  the  metamorphic  hills  about ;  and  hence  meta- 
morphism  was  antecedent  to  the  deposition  of  the  conglomerates.  The 
plane  of  demarkation  separating  this  group  from  the  Tonto  group  is 
very  great.  At  least  10,000  feet  of  beds  were  flexed  and  eroded  in  such 
a  manner  as  to  leave  but  fragments  in  the  synclinals.  Then  followed 
a  period  of  erosion,  during  which  beds  of  extravasated  material  were 
poured  over  the  fragments,  and  these  igneous  beds  also  were  eroded 
into  valleys  prior  to  the  deposition  of  the  Tonto  group.  Fossils  have 
been  found  at  the  base  of  the  Grand  canyon  series,  but  they  are  not 
well  preserved  and  little  can  be  made  of  them.  Still,  on  geological 
evidence,  these  beds  are  considered  Silurian. 
Walcott,71  in  1883,  describes  below  the  Tonto  a  great  series  of 
unconformable  sediments  which  are  divided  into  two  groups,  the  Chuar 
and  Grand  canyon,  between  which  there  is  an  unconformity  by  erosion. 
The  lower  or  Grand  canyon  group  is  made  up  of  an  immense  mass  of 
sandstones  and  interbedded  greenstones,  and  the  Chuar  group  is  a 
series  of  sandy  and  clay  shales.  The  Archean  at  the  base  of  the  Grand 
canyon  group  consists  of  thin-bedded  quartzites  broken  by  intrusive 
veins  of  a  flesh-colored  granite,  the  layers  of  quartzite  standing  nearly 
