THE   CORDILLERAS.  869 
slates.  If  the  structural  relations  were  regarded  as  conclusive  evi- 
dence, the  whole  series  would  necessarily  be  considered  metamorphic ; 
but  there  is  little  reason  to  doubt  that  the  granite  is  eruptive.  The 
metamorphism  in  the  limestone  is  complete  and  resembles  the  coarsely 
crystalline  white  limestone  of  Sussex  County,  N.  J.  There  is  no 
indication  as  to  the  age  of  the  limestone  or  quartz  rock,  but  there  is 
some  reason  to  regard  them  as  Carboniferous,  for  these  are  the  nearest 
known  formations  of  limestone  which  are  recognizable  by  fossils. 
On  the  section  of  the  Canada  de  las  Uvas  the  rocks  are  similar  to 
those  of  the  western  slopes  of  the  Tejon.  Along  Mohave  River  the 
rocks  consist  of  metamorphic  slates,  very  compact  and  so  much 
changed  as  to  resemble  granite.  In  the  Colorado  Desert  most  of  the 
metamorphic  rocks  are  highly  laminated  and  contain  lenticular  beds 
of  limestone.  In  the  gold  region  talcose  and  clay  slates  are  the  pre- 
vailing rocks,  and  in  general  present  a  low  degree  of  metamorphism. 
Next  to  the  slate  in  importance  is  white  crystalline  limestone. 
Emory,104  in  1857?  states  that  in  southern  California  there  is  a  great 
preponderance  of  crystalline  metamorphic  granite  pertaining  to  the 
older  Paleozoic  series  of  rocks  and  an  entire  absence  of  any  member 
of  the  lower  Paleozoic  or  secondary  rocks  in  their  regular  stratified 
character.  The  central  axes  are  represented  by  somewhat  variable 
granite,  assuming  in  some  places  a  close  syenitic  texture,  while  at 
other  places  there  is  a  preponderance  of  mica.  Belonging  with  the 
granitic  series,  particularly  on  the  eastern  side  of  the  range,  are  mica 
and  talcose  slates. 
Newberry,105  in  1861,  describes  the  great  mass  of  the  Peninsular 
Mountains,  east  of  San  Diego,  as  composed  of  granitic  and  gneissoid 
rocks  which  are  similar  to  most  of  the  granites  of  the  other  systems 
of  the  Colorado:  that  is,  a  predominance  of  the  feldspathic  over  the 
hornblendic  ingredients.  Where  the  Colorado  cuts  through  the- 
Chocolate  Mountains  they  are  composed  of  gneisses  traversed  by 
veins  of  granite  and  quartz.  The  gneissoid  rocks  are  frequently 
foliated  and  much  convoluted.  Their  aspect  is  such  as  to  lead  an 
observer  more  readily  to  refer  them  to  a  metamorphic  origin  than  any 
other  rocks  seen  on  the  route.  The  great  mass  of  Monument  Moun- 
tains is  a  coarse,  massive  feldspathic  granite.  On  both  sides  of  the 
granitic  axis  are  highly  metamorphosed  conglomerate  and  sandstone. 
The  principal  mass  of  the  Mohave  Mountains  is  composed  of  white 
granite,  traversed  by  numerous  veins  of  quartz.  The  Black  Moun- 
tains as  a  whole  are  characterized  by  prominence  of  eruptive  rocks, 
such  as  massive  granite,  trap,  porphyry,  and  trachyte,  and  rarity  of 
gneiss,  mica  slate,  clay  slate,  etc.,  which  are  probably  metamorphic. 
In  the  lower  Colorado  Canyon,  unconformably  below  the  Potsdam 
sandstone,  is  granite,  which  is  cut  by  veins  of  quartz  and  red  syenite. 
This  sandstone  is  somewhat  metamorphosed,  but  its  consolidation  i- 
