vanhise.]  THE    CORDILLERAS.  325 
the  intrusives  are  regarded  simply  as  parts  of  the  main  mass  which 
have  become  perfectly  fluid  and  therefore  locally  take  on  eruptive 
forms.  Lawson  declines  to  carry  the  term  metamorphic  over  to  the 
plastic  material  and  speaks  of  it  as  a  subcrustal  magma.  As  the  real 
character  of  such  granite-gneiss-schist  complexes  is  a  question  which 
concerns  not  only  the  Colorado  ranges,  but  almost  every  other  pre- 
Cambrian  region  of  North  America,  the  discussion  of  this  question  is 
deferred  for  the  general  chapter.  It  is,  however,  x>lain  that  in  the  moun- 
tain ranges  of  Colorado  is  a  thoroughly  crystalline,  intricate,  funda- 
mental complex  like  that  found  in  most  of  the  pre-Cambrian  areas 
already  considered. 
Besides  these  crystallines  there  are  at  least  two  areas  in  which  unmis- 
takable pre-Cambrian  elastics  are  present.  These  are  the  districts  of 
Big  and  Little  Thompson,  South  Boulder,  Coal  and  Ealston  creeks  in 
the  Front  range,  and  the  district  of  the  Quartzite  mountains  in  the  San 
Juan  region.  It  is  also  probable  that  the  quartzites  and  mica- schists 
of  northern  New  Mexico,  described  by  Stevenson,  is  a  third  series, 
although  the  relations  of  these  beds  to  the  other  rocks  are  not  indicated. 
The  great  beds  of  white  quartzite  and  the  granite- conglomerate  in  the 
neighborhood  of  Santa  Fe  strongly  suggests  that  here  is  a  clastic  series, 
the  granite- con  glomerate  probably  being  a  recomposed  rock.  A  fourth 
great  series  which  possibly  falls  among  the  rue-Cambrian  elastics  is 
that  seen  by  Cross  in  the  neighborhood  of  Salida. 
In  the  Front  range  the  descriptions  of  Marvine  and  Lakes  agree  that 
there  is  an  apparent  gradation  from  the  clastic  quartzite  and  mica- schist 
series  to  the  gneisses  and  gneissoid  granites,  although  Lakes  states 
that  the  transition  is  somewhat  abrupt.  Two  explanations  may  be  ap- 
plied here :  First,  there  may  be  a  real  physical  break  which  has  not 
been  detected  between  the  elastics  and  the  crystallines.  In  favor  of  this 
hypothesis  is  the  fact  that  quartzites  are  found  nowhere  else  in  the  vast 
area  of  the  Front  range,  and  that  nowhere  else  are  there  any  rocks  which 
are  even  described  as  having  any  evidence  of  fragmental  character,  un- 
less foliation  be  taken  as  such  evidence.  If  this  clastic  series  and  the 
great  complex  of  granite,  gneiss  and  schist  are  of  the  same  origin  and 
age,  it  is  certainly  strange  that  nowhere  except  in  this  very  restricted 
area  do  beds  of  quartzite  or  quartz -schist  occur.  Also  the  presence  of 
genuine  granitic  pebbles  in  the  conglomerates  at  least  shows  that  there 
existed  an  earlier  granite  from  which  debris  was  derived.  Second,  those 
who  believe  that  the  fine-grained  gneisses,  completely  crystalline  schists 
and  granites  are  all  really  of  eruptive  origin,  the  foliation  being  but 
evidence  of  powerful  dynamic  action,  will  probably  maintain  that  this 
clastic  series  is  the  more  ancient  one  and  has  been  cut  and  metamorphosed 
by  the  intrusion  of  the  igneous  rocks. 
In  the  Quartzite  mountains  the  evidence  that  the  fragmental  slate 
and  quartzite  series  is  more  recent  than  the  granite-gneiss-schist  com- 
plex is  far  more  weighty.     Here  an  intricate  complex  of  irregularly 
