van  hish.]  DISCUSSIONS    OF    PKINCIPLKS.  449 
tion  well  defined  crystals  are  of  great  rarity;  even  microscopic  apatite, 
the  best  presented  species,  is  generally  crushed  and  dislocated ;  micas 
are  distorted,  and  all  feldspars  are  more  or  less  fragmentary.  A 
marked  contrast  is  observable  at  the  upper  extreme.  Here  many 
micas,  hornblendes,  garnets,  and  even  feldspars  are  nearly,  if  not  quite, 
completed  crystals.  The  exceptions  to  this  are  those  places  already 
described,  where  local  compression  has  broken  up  the  original  arrange- 
ment of  the  crystalline  ingredients. 
Nearly  every  considerable  mountain  body  between  the  Wasatch  and 
the  California  line  shows  in  the  lowest  horizons  exposures  of.  one  or 
more  bodies  of  granite.  These  are  classified  into  four  groups  upon 
penological  grounds.  The  first  type  consists  of  quartz,  orthoclase,  an 
unimportant  amount  of  plagioclase,  and  muscovite,  with  a  small  quan- 
tity of  microscopical  apatite.  These  are  all  west  of  Eeese  river,  longi- 
tude 117°.  These  are  all  associated  with  the  Nevada  type  of  Archean 
crystalline  schists  composed  of  quartz,  biotite,  muscovite,  and  mag- 
netite, or  quartz,  hornblende,  and  magnetite.  As  to  the  age  of  the  gran- 
ites of  this  type  there  are  practically  no  data  available.  At  one  place  it 
is  intimately  involved  with  the  crystalline  schists  and  is  overlain  uncon- 
formable7 by  the  Carboniferous.  There  is  little  doubt  that  it  is  Archean 
but  its  reference  to  that  period  is  on  general  lithological  grounds.  The 
second  type  is  of  the  same  composition  as  the  first,  except  that  biotite 
is  substituted  for  muscovite.  It  has  a  range  from  the  Ombe  mountains 
west  of  Salt  lake  desert  to  the  California  line.  The  third  type  is  like 
the  second  except  that  biotite  and  hornblende  are  found  together.  This 
distribution  is  coextensive  with  that  of  the  second  type.  The  fourth 
type  is  the  most  complex  in  its  petrological  features  of  any  of  the  fam- 
ilies of  granite,  and  consists  of  quartz,  orthoclase,  plagioclase,  often 
equal  in  quantity  to  the  orthoclase  and  sometimes  exceeding  it,  usually 
a  high  percentage  of  biotite  and  hornblende,  titanite,  and  a  high  propor- 
tion of  microscopic  apatite.  Between  this  class  and  the  diorites  that 
are  unusually  rich  in  orthoclase  there  is  but  little  difference,  although 
there  is  little  danger  of  ever  confounding  the  granitoid  diorite  with  the 
dioritic  members  of  the  fourth  type.  These  granites  are  the  most  prom- 
inent as  regards  geographical  distribution  of  the  truly  eruptive  varie- 
ties observed  in  the  Cordilleras.  When  the  different  types  of  granite 
are  seen  in  apposition  so  as  to  give  a  clew  as  to  their  relative  ages  it  is 
found  that  they  occur  in  the  order  given.  In  denominating  these  groups 
of  granite  as  eruptive  it  is  only  intended  to  indicate  that  in  their  rela- 
tions to  the  contiguous  Archean  schists  they  have  the  appearance  of 
intrusive  bodies,  and  that  in  their  interior  structure  and  general  mode 
of  occurrence  there  are  none  of  those  evidences  of  alliances  to  the  crys- 
talline schists  which  are  observed  in  the  granitoid  gneisses  of  so  many 
localities,  especially  in  the  Kocky  mountain  region.  In  so-called  erup- 
tive granites  there  is  neither  parallelism  of  general  bedding  nor  of  inte- 
rior arrangement  of  the  minerals,  and  the  most  ordinary  phenomenon 
Bull.  86 29 
