THE   CORDILLERAS.  787 
of  shales,  quartzites,  sandstones,  and  slates.  The  upper  250  feet  of 
shale  bears  the  Olenellus  fauna,  while  other  layers,  although  in  a  most 
excellent  condition  for  the  finding  of  fossils,  did  not  reveal  any. 
The  Olenellus  horizon  is  placed  at  the  base  of  the  Middle  Cambrian 
and  the  great  remaining  part  as  Lower  Cambrian. 
Emmons  (S.  F.),50  in  188G,  discusses  the  possibility  of  the  post- 
Cambrian  eruptive  character  of  the  Cottonwood  granite.  This  body 
occupies  an  area  of  about  7  by  15  miles,  and  a  thickness  of  some  5 
miles  of  sedimentary  rocks  abuts  against  its  northern  side,  the  prin- 
cipal members  sweeping  around  and  in  part  covering  its  eastern  por- 
tion and  continuing  southward  in  an  almost  horizontal  position. 
There  is  no  especial  disturbance  of  these  beds  in  contact  with  the 
granite  so  far  as  observed.  Neither  are  any  masses  or  fragments  of 
sedimentary  rock  included  in  the  granite.  Regional  metamorphism 
has  changed  the  sandstone  to  quartzite  and  the  limestone  to  marble, 
and  porphyry  dikes  cross  the  sedimentary  strata,  but  these  have  no 
necessary  connection  with  the  granite.  If  the  granite  is  an  intrusive 
mass  cutting  the  Carboniferous  strata,  it  is  necessary  to  believe  that 
it  has  assimilated  or  eaten  up  more  than  500  cubic  miles  of  sedimen- 
tary rocks.  If  it  has  done  this,  it  has  left  no  trace  of  fusion  in  the 
adjoining  rock,  and  it  shows  in  its  own  structure  and  position  no 
marked  variation  from  that  of  a  normal  rock.  It  is  further  difficult 
to  understand  where  the  great  supply  of  heat  to  do  this  work  is 
to  be  obtained. 
Walcott,21  in  1889,  places  the  Olenellus  horizon  at  the  base  of  the 
Cambrian,  and  regards  the  great  series  of  conformable  siliceous  rocks, 
11,000  feet  thick,  below  this  zone  as  pre-Cambrian  or  Algonkian. 
Van  Hise,38  in  1889,  made  an  examination  of  several  canyons  of 
the  Wasatch.  While  the  Cottonwood  granite  mass  has  a  regular 
structure  which  is  seen  in  the  great  cliffs,  it  is  apparently  completely 
massive,  even  in  huge  blocks.  The  apparent  lamination  is  due  to  the 
parallel  arrangement  of  the  minerals,  which  have  crystallized  with 
their  longer  axis  in  the  same  direction.  The  lamination  of  (he  granite 
is  not  more  marked  than  is  the  case  with  some  of  the  unmistakable 
gabbros  of  the  Keweenaw  series.  An  examination  of  the  granite  in 
thin  section  shows  that  the  feldspars  have  universally  a  well-marked 
and  beautiful  zonal  structure,  such  as  is  known  only  in  eruptive  rocks. 
Sections  of  some  of  the  black  bowlder-like  areas  so  common  in  the 
granite  differ  from  the  mass  of  granite  only  in  that  hornblende  is 
more  plentiful.  In  places  the  sedimentary  rocks,  and  especially  the 
limestones,  are  exceedingly  metamorphosed.  In  one  place,  near  the 
head  of  Little  Cottonwood  Canyon,  at.  a  contact  with  the  granite,  it 
was  exceedingly  difficult  in  the  field  to  tell  where  the  white  granite 
ended  and  the  crystalline  marble  began.  In  thin  section  there  i^  no 
difficulty  in  separating  the  marble  and  the  granite,  so  that  there  LS  n<» 
