THE   CORDILLERAS.  77*7 
pre-Cambrian  granitic  intrusives  are  absent.  Here  also  they  are  re- 
ferred to  the  pre-Cambrian. 
Jaggar  and  Palache,30  in  1905,  map  and  describe  the  geology  of 
the  Bradshaw  Mountains  quadrangle,  in  Arizona.  The  Yavapai 
schists,  assigned  to  the  Algonkian,  are  made  up  of  7,000  feet  of  schis- 
tose sedimentary  rocks  and  schists  of  igneous  and  doubtful  origin, 
compressed  into  isoclinal  folds  and  rendered  schistose  by  a  horizontal 
force  acting  from  northwest  to  southeast.  The  conglomerate  con- 
tains pebbles  of  granite,  quartz,  schist,  and  quartzite,  indicating  a 
basement  made  up  of  these  rocks,  but  such  a  basement  has  not  been 
definitely  located  within  this  district.  The  Yavapai  formation  is 
intruded  by  acidic  and  basic  igneous  rocks,  plutonics  and  surface, 
some  of  them  probably  Algonkian  and  some  of  them  doubtfully  Ter- 
tiary. 
The  evidence  of  the  pre-Cambrian  age  of  the  Yapavai  schists  con- 
sists in  their  similarity  to  certain  schists  intruded  by  diorite  at 
Jerome  to  the  northeast,  which  are  overlain  by  Paleozoic  rocks  un- 
conformably,  and  in  their  similarity  with  Walcott's  lower  or  Vishnu 
series  of  the  Grand  Canyon  district. 
Lindgren,31  in  1903  and  1905,  maps  and  describes  the  geology  of 
the  Clifton  quadrangle,  in  Arizona.  The  lowest  rocks  are  the  Pinal 
schists,  consisting  of  quartz  sericite  schists,  probably  of  sedimentary 
origin,  and  smaller  bands  and  masses  of  amphibolitic  rock.  The 
schist  is  intruded  by  granite  of  pre-Cambrian  age.  Resting  uncon- 
formably  on  these  rocks  is  the  Coronado  (Cambrian)  quartzite. 
Ransome,32  in  1908,  regards  the  Vishnu  series  of  the  Grand  Canyon 
as  consisting  of  fine-grained  gneiss  cut  by  red  granite,  probably  of 
Archean  age.  This  had  been  described  by  Walcott  as  sedimentary 
and  probably  Algonkian.  The  Pinal  schists  of  the  range  districts  to 
the  south,  previously  correlated  with  the  Vishnu  series  because  of  its 
supposedly  sedimentary  character,  are  now  correlated  with  the  Chuar 
and  Unkar  series. 
SUMMARY  OF  PRESENT  KNOWLEDGE. 
The  geological  map  of  Arizona  still  contains  many  blanks.  The 
cores  of  many  of  the  mountain  ranges  in  a  general  zone  trending 
north  west -southeast  through  the  central  part  of  the  State  consist 
largely  of  granites,  gneisses,  and  schists,  probably  of  pre-Cambrian 
age.  It  is  likely  that  with  the  granite  mapped  as  pre-Cambrian  there 
are  included  granites  of  later  age.  The  granites  and  some  of  the 
gneisses  are  of  igneous  origin;  the  schists  and  most  of  the  gneisses 
are  of  unknown  origin.  Ransome  and  Lindgren  concluded  thai  the 
Pinal  schist  of  the  Globe,  Bisbee,  and  Clifton  districts  represented 
metamorphosed  arkose  or  grits,  and  was  to  be  correlated  with  the 
Vishnu  "terrane"  of  the  Grand  Canyon.     A  similar  conclusion  was 
