778  PRE-CAMBRIAN   GEOLOGY   OF    NORTH    AMERICA. 
reached  by  Jaggar  for  the  basal  series  of  the  Bradshaw  quadrangle. 
This  correlation,  however,  was  made  on  a  misunderstanding  as  to 
the  nature  of  the  Vishnu,  which  had  been  described  by  Walcott  as 
a  metamorphosed  quartzite,  but  which  is  now  regarded  by  Ransome 
as  gneiss.  Ransome  now  correlates  the  Pinal  schist  with  the  Chuar 
and  Unkar  groups. 
In  the  Grand  Canyon  there  is  a  basal  complex,  Powell's  "  Grand 
Canyon  schists,"  described  by  Van  Hise  as  typically  Archean  or  base- 
ment complex  in  aspect,  including  granites  and  gneisses  in  consider- 
able variety,  a  hard  hornblende  gneiss  being  the  oldest  in  the  series. 
Walcott  describes  this  complex  as  consisting  of  micaceous  schists  and 
quartzite  cut  by  granite,  which  he  finds  on  the  north  side  of  the  can- 
yon south  of  Vishnu's  Temple  and  calls  the  Vishnu  "  terrane,"  doubt- 
fully referring  it  to  the  Algonkian.  This  complex  Van  Hise  did  not 
examine  in  the  locality  described  by  Walcott.  Ransome  and  Lind- 
gren  believe  that  Powell's  "  Grand  Canyon  schists,"  Walcott's  Vishnu 
"terrane,"  and  Van  Hise's  '"  Basement  complex"  are  probably  the 
same,  and  doubt  the  existence  of  quartzites.  The  complex  of  gran- 
ites, gneisses,  and  schists  was  almost  completely  leveled  before  the 
deposition  of  the  next  overlying  series.  The  unconformably  over- 
lying series  is  the  Grand  Canyon  series,  11,950  feet  thick,  consisting 
of  two  groups — the  Unkar,  6,830  feet  thick,  and  the  Chuar,  5,120 
feet  thick. 
The  Unkar  group  consists  of  sandstones  and  limestones  interstrati- 
fied  with  basalts,  and  has  at  its  base  a  conglomerate  composed  largely 
of  pebbles  derived  from  the  upturned  edges  of  the  pre-Unkar  rocks. 
Resting  upon  the  Unkar  group  with  a  slight  unconformity  is  the 
Chuar  group.  It  consists  of  shales,  sandstones,  shaly  limestones, 
and  limestones.  In  the  middle  of  the  lower  portion  of  the  shales  and 
limestones  of  the  Chuar  group  is  a  sparse  fauna,  consisting  of  a 
minute  discinoid  or  patelloid  shell,  a  small  Lingula-like  shell  (which 
may  be  a  species  of  Ilyolithes),  and  a  fragment  of  what  appears  to 
be  the  pleural  lobe  of  a  segment  of  a  trilobite  belonging  to  a  genus  or 
allied  to  the  genera  Olenellus,  Olenoides,  and  Paradoxides.  There 
is  also  a  Stromatopora-like  form  that  is  probably  organic.  Resting 
with  a  great  unconformity  upon  the  Chuar  are  the  strata  of  the  Tonto 
or  middle  Cambrian  group.  During  the  time  represented  by  this  un- 
conformity the  sediments  of  the  Grand  Canyon  series  were  elevated, 
faulted,  somewhat  flexed,  and  eroded,  so  that  the  entire  series  was  cut 
through,  and  the  area,  including  the  more  resistant  Vishnu  rocks, 
was  base-leveled.  The  length  of  time  required  by  this  unconformity 
is  believed  to  be  longer  than  the  period  of  lower  Cambrian  sedi- 
mentation, and  the  Grand  Canyon  series  is  therefore  placed  in  the 
Algonkian.  The  Grand  Canyon  series  has  lithological .  analogies 
with  the  Keweenawan  of  Lake  Superior  and  the  Llano  series  of  Texas, 
