796  PRE-CAMBRIAN    GEOLOGY   OF    NORTH   AMERICA. 
feet  thick,  in  beds  from  half  an  inch  to  6  feet.  Intercalated  with  the 
limestones  are  gneiss  and  porphyries  ver}^  like  those  in  the  Gosiute 
Range.  The  upper  beds  pass  through  a  transition  into  the  pure 
quartzites.  The  Humboldt  Archean  schists  have  a  family  likeness 
with  those  of  the  Farmington  region  of  the  Wasatch  and  those  of  the 
Medicine  Bow. 
In  the  Cortez  Range  a  central  body  of  granite  is  invaded  by  sye- 
nites, and  is  overlain  on  the  west  by  a  quartzite,  which  is,  for  the  sake 
of  convenience,  referred  to  the  Weber. 
In  the  Shoshone  Range  the  stratified  series  dip  away  from  the  cen- 
tral mass,  which  has  rather  the  appearance  of  an  intrusive  core.  From 
their  likeness  to  other  known  Archean  rocks,  and  for  want  of  reasons 
to  the  contrary,  these  schists,  together  with  the  granite,  are  referred 
to  the  Archean.  Regular  parallel  divisional  planes  are  seen  in  the 
granite,  so  as  to  give  it  an  appearance  of  stratification,  but  as  it  pene- 
trates the  schists  in  the  form  of  a  dike,  there  is  no  doubt  of  its  eruptive 
origin. 
In  the  Havallah  Range,  associated  with  the  older  granites  are  intru- 
sive granite  bodies,  but  such  occurrences  are  exceptional  along  the 
area  of  the  fortieth  parallel. 
In  the  West  Humboldt  Range  a  variety  of  crystalline  schists  are 
found  unconformably  upon  the  granite,  no  tendency  toward  a  passage 
between  the  two  rocks  being  shown,  and  dikes  of  granitic  material 
invade  the  schists.  In  the  schists  are  roundish  areas  of  quartz, 
which  might  be  explained  on  the  supposition  that  they  are  the  pebbles 
of  conglomerates,  but  they  are  more  probably  an  aggregation  formed 
during  metamorphism. 
In. the  Montezuma  Range  the  granite  of  Trinity  Peak  is  undoubt- 
edly of  eruptive  origin,  as  may  be  determined  from  its  general 
habitus  and  from  its  penetrating  the  Archean  schists  in  well-defined 
dikes. 
In  the  Pahtson  Range  the  Archean  nucleus  consists  of  crystalline 
schists,  a  limited  amount  of  granite,  and  a  subsequent  granite  which 
has  cut  through  the  older  granites  and  schists.  These  are  all  cut  by 
dikes  of  later  age,  but  supposed  to  be  Archean. 
The  Truckee  Range  is  composed  of  schists  and  granite  representing 
two  periods  of  formation. 
The  Pea  Vine  Mountains  consist  of  a  series  of  conformable,  highly 
altered  beds,  striking  N.  50°  to  65°  E.,  made  up  for  the  most  part  of 
fine-grained  quartzite  strata,  riven  in  every  direction  with  minute  fis- 
sures, which  are  filled  with  ferruginous  material. 
It  is  remarked  that  in  the  absence  of  any  granitic  dikes  penetrating 
the  stratified  series,  or  of  peculiar  local  metamorphism,  or  general 
evidence  of  intrusion,  the  bodies  are  usually  referred  to  the  Archean. 
Only  in  cases  where  the  granite  is  actually  seen  to  penetrate  the  open- 
