THE   CORDILLERAS.  793 
vada,  is  a  mass  of  Archean  rocks,  which  acts  as  the  axis  of  an  anti- 
clinal fold  and  upon  which  rest  unconformably  the  Devonian  and 
Carboniferous  strata.  The  southern  part  of  the  range  is  composed 
of  granite  in  two  large  areas,  which  at  White  Cloud  Peak  possesses 
the  characteristics  of  an  eruptive  granite,  there  being  no  distinct  lines 
of  bedding,  although  divisional  planes  are  noticeable.  The  northern 
granite  mass  is  unconformably  overlain  by  a  series  of  quartzites, 
hornblende  schists,  and  gneisses  which  contain  beds  of  dolomitic  lime- 
stone from  1  to  6  feet  in  thickness,  separated  by  micaceous  quartzites 
and  mica  schists.  This  series,  estimated  in  the  northern  part  of  the 
range  to  be  from  5,500  to  G,000  feet  in  thickness,  is  best  seen  on  Clover 
Canyon  and  Boulder  Creek.  There  is  every  gradation  between  the 
coarse  gneissoid  phases  and  the  fine-grained  mica  schists.  The  gran- 
ite of  the  Humboldt  is  similar  to  the  Laurentian  of  the  Appalachian, 
while  the  unconformably  overlying  series  closely  resembles  the  east- 
ern Huronian.  In  the  Southern  Shoshone  Range  an  original  Arch- 
ean island  is  wrapped  around  by  fine-grained  micaceous  slate.  The 
Archean  granite  of  Ravenswood  Peak  has  remarkably  regular  bed- 
ding planes,  apparently  conformable  to  those  of  the  overlying  slates, 
which  give  it  the  appearance  of  being  a  stratified  granite,  although 
it  at  the  same  time  traverses  the  slates  in  dikes.  The  Ravenswood 
Peak  granite  to  the  east  is  essentially  different  from  the  Archean 
granite  and  is  evidently  of  later  origin.  In  the  West.  Humboldt 
Range  the  granite  shows  structural  planes.  Along  its  northern  and 
western  edge  it  is  overlain  by  a  series  of  metamorphic  schists  and 
gneisses,  which  are  in  turn  overlain  by  fine,  white,  knotted  schists. 
The  strike  of  these  beds  is  N.  38°  E.,  and  they  stand  nearly  vertical. 
The  contact  of  the  granite  and  schist  shows  in  a  horizontal  plane 
irregular  angular  intrusions  of  the  former  into  the  latter,  masses  of 
schists  lying  in  the  granite  and  extending  as  promontories  from  the 
main  mass  for  400  or  500  feet.  The  line  of  demarcation  between  the 
two  bodies  is  easily  observed,  and  there  seems  to  be  no  tendency  i'<>r 
the  schists  to  pass  by  gradation  into  the  granite.  Dikes  penetrate 
both  the  granite  and  the  schists.  The  range  is  regarded  as  an  anti- 
clinal fold.  In  the  Montezuma  Range  are  slates  and  schists  which 
rest  unconformably  upon  the  granite.  The  Pahtson  Mountains  con- 
sist almost  entirely  of  granite  and  crystalline  schists,  which  are 
cut  by  numerous  dikes,  the  whole  being  regarded  as  Archean. 
because  the  dikes  do  not  cut  later  eruptive  granite-,  which  are  found 
in  considerable  quantity,  and  differ  markedly  from  those  which  are 
regarded  as  Archean.  In  the  Truckee  Range  are  found  quartzitic 
schists  and  hornblendic  rocks  with  both  older  and  later  types  of  gran- 
ite. The  metamorphic  schists  cut  by  intrusive  granites  referred  to 
the  Archean  occupy  but  a  small  area,  the  Later  granites  making  up 
the  greater  part  of  the  range.     In  the  Lake  Range  are  granite  and 
