800  PRE-CAMBRIAN    GEOLOGY    OF    NORTH   AMERICA. 
the  exception  of  those  in  the  Snake  Range  and  Colorado  River  areas. 
In  the  Snake  Range  intrusive  phenomena  are  to  be  observed,  but 
Spurr  believes  these  to  be  associated  with  later  rocks,  similar  in 
composition  to  an  earlier  granitic  mass,  which  is  probably  pre- 
Cambrian. 
Sedimentary  rocks,  apparently  lacking  fossils  and  underlying 
Cambrian  rocks,  are  mapped  by  the  geologists  of  the  Fortieth  Parallel 
Survey  in  the  Schell  Creek,  Egan,  Pogonip,  Snake  River,  and  Pinon 
ranges.  These  geologists  call  them  Cambrian,  and  call  attention  to 
their  similarity  to  the  quartzites  of  the  Wasatch  Mountains.  No 
systematic  search  for  fossils  has  been  made  in  these  beds.  Although 
the  Olenellus  fauna  has  been  found  in  many  places  in  the  overlying 
Cambrian  beds,  Walcott  is  not  sure  that  he  has  found  the  bottom  of 
this  fauna.  Hence  the  underlying  beds  may  be  Algonkian  or  Cam- 
brian. They  are  here  provisionally  assigned  to  the  Algonkian  be- 
cause of  their  apparent  lack  of  fossils  and  their  occurrence  beneath 
the  known  Cambrian.  In  Idaho  and  Montana  a  sedimentary  series 
in  a  similar  position  has  been  found  to  be  pre-Cambrian. 
In  the  Schell  Creek  Range  the  probable  Algonkian  is  represented 
by  heavy  bodies  of  quartzite.  In  the  Egan  Range  the  probable  Al- 
gonkian is  represented  by  a  series  of  thoroughly  vitrified  quartzites, 
several  thousand  feet  thick,  containing  quartzitic  and  micaceous 
schists.  In  the  Pogonip  Range  it  is  represented  by  micaceous,  arena- 
ceous, and  argillaceous  slates  and  shales  and  by  vitreous  quartzite, 
the  series  being  of  undetermined  thickness.  In  the  Pinon  Range  it 
is  represented  by  quartzites' underlain  by  mica  schists  and  quartzitic 
schists,  having  a  total  thickness  of  5,000  feet. 
In  the  Snake  Range  of  eastern  Nevada  are  quartzites  and  ar- 
gillaceous and  siliceous  schists  underlying  shales  in  which  is  found 
the  Olenellus  fauna.  At  the  base  of  the  quartzite  is  a  conglomerate 
100  to  200  feet  thick,  carrying  fragments  of  granite  and  quartz 
porphyry  from  underlying  granitic  rocks.  Weeks  cites  the  Snake 
Range  as  the  only  one  known  in  the  Great  Basin  in  which  the 
granitic  rocks  have  been  found  to  be  separated  from  pre- Olenellus 
sediments  by  a  marked  unconformity. 
The  Colorado  River  Algonkian  is  described  under  Arizona,  section 
3  (pp.  777-779). 
SECTION  6.     COLORADO. 
SUMMARY    OF   LITERATURE. 
FRONT  RANGE   NORTH  AND  EAST  OF  THE  ARKANSAS.® 
Long,60  in  1823,  describes  granite  as  succeeding  pudding  stone  or 
conglomerate  on  Defile  Creek.  The  granite  is  coarse  grained  and 
rapidly  disintegrates. 
«  For  southward  continuation  of  Front  Range,  see  section  2,  this  chapter,  pp.  768-770. 
