768  PEE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
ites,  and  various  other  rocks,  some  of  Tertiary  age.  These  rocks  are 
felsites,  quartz  porphyries,  rhyolites,  and  andesitic  rocks.  The  lime- 
stone, probably  Cretaceous,  is  found  resting  in  thick  beds  upon  crys- 
talline slate  in  the  sierra  which  passes  through  the  center  of  the 
isthmus,  in  the  same  manner  as  in  the  other  regions  which  we  have 
summarily  sketched. 
According  to  Sapper  and  Bose,a  the  Archean  is  found  represented 
upon  the  extreme  west  of  the  Sierra  Madre  de  Chiapas  by  gneiss  and 
some  phyllites.  Between  Dolores  and  Frontera  the  sierra  is  com- 
posed of  biotite  gneiss,  while  in  the  valley  of  Cintalapa  there  is  horn- 
blendic  gneiss.  Between  the  narrow  bands  or  belts  of  ciystalline 
schist  which  Sapper  examined  in  the  sierra  there  are  mica  slates  in 
addition  to  gneiss  and  schists.  Bose  thinks  it  probable  that  the 
Archean  crystalline  slates  of  Chiapas  occupy  in  reality  an  area  greater 
than  that  which  has  hitherto  been  supposed. 
SECTIONS.     NEW   MEXICO,  INCLUDING   PART    OF    THE 
FRONT  RANGE  OF  SOUTHERN  COLORADO. 
SUMMARY    OF   LITERATURE. 
Wislizenus,4  in  1848,  states  that  granitic  rocks  prevail  in  the 
mountains  about  Santa  Fe  and  for  some  distance  to  the  south.  These 
are  associated  with  porphyry  and  trap. 
Blake,5  in  1856,  describes  ridges  of  met  amorphic  slate  in  the  Santa 
Fe  Mountains,  upon  the  edges  of  which  rest  horizontal  Carboniferous 
strata. 
Loew,6  in  1875,  states  that  the  mountains  between  Santa  Fe  and 
Las  Vegas  contain  Azoic  rocks  which  are  chiefly  granite  and  syenite. 
At  Santa  Fe  Creek  gneiss  is  accompanied  by  Primitive  clay  slate  and 
syenite.  Veins  of  fine-grained  gneisses  occur  in  a  coarse  aplite  or 
granulite  also  intersected  by  syenite  seams. 
Gilbert,7  in  1875,  describes  the  range  region  of  western  New 
Mexico  and  eastern  Arizona.  Nortlrwest  of  the  Burro  Mountains  for 
50  miles  are  islands  of  Archean  and  Paleozoic  rocks.  The  most  con- 
spicuous of  the  former  is  a  deep-red  granite.  In  the  Santa  Rita 
Mountains  the  axial  rocks  are  Archean  schists.  On  the  eastern  border 
of  the  Plateau  region  is  a  chain  of  ranges  which  coalesces  with  the 
Rocky  Mountains  of  Colorado  and  consists  mainly  of  Archean  and 
Carboniferous  rocks.  The  whole  front  of  the  Sandia  Mountains  ex- 
cept the  crest  is  Archean. 
St.  John,8  in  1876,  describes  the  Black  Mountains  as  a  lofty  granite 
barrier.  The  upper  canyon  of  the  Cimarron  is  composed  of  granitic 
rocks,  with  which  are  associated  micaceous  schists  and  hard  quartz- 
ose  rocks.    In  the  Raton  Hills  are  granitic  igneous  rocks,  the  relations 
a  Loc.  cit. 
