vanhise.]  THE    CORDILLERAS.  321 
from  75°  to  85°.  At  one  place  the  clip  of  the  schistose  structure  was 
observed  to  be  as  flat  as  10°  or  15°. 
The  quartzitic  area  is  in  places  conglomeratic.  The  rock  is  for  the 
most  part  a  rather  pure  white  or  gray  vitreous  quartzite,  although  oc- 
casionally it  shows  more  or  less  of  a  slaty  appearance.  Nowhere  in 
the  quartzite  was  found  any  hornblende- schist  in  dike-like  forms  such 
as  occur  in  the  granite,  or  any  layers  which  could  possibly  be  mistaken 
for  the  black  or  white  gneissoid  phases  of  rock  which  occur  so 
abundantly  in  the  granite  area  and  have  such  intricate  relations  with 
the  granite.  The  dips  of  the  quartzites  are  also  for  the  most  part  high, 
being  from  60°  to  70°.  In  the  quartzites,  as  in  the  granites,  there  are 
great  local  variations  in  the  strike  and  dip  of  the  rock.  Upon  both 
sides  of  the  quartzite  area  where  the  change  to  granite  occurs  no  evi- 
dence whatever  was  seen  of  a  transition  between  the  two  classes  of 
rocks.  In  neither  were  the  quartzites  and  granites  in  contact;  they 
were  found  however,  a  few  paces  apart.  At  the  southern  boundary, 
while  the  two  rocks  were  not  actually  found  in  contact,  there  is  a 
marked  discordance  in  the  strike  and  dip  of  the  schistose  structure  of 
the  granite  and  of  a  series  of  sharply  folded  anticlines  and  synclines 
of  quartzites  which  are  adjacent  to  the  granite. 
What  is  said  by  Endlich  as  to  the  sharp  contrast  between  the  sedi- 
mentaries  and  granite  may  mean  the  contrast  between  the  black  horn- 
blende-schists and  gneisses  with  the  coarse  granitoid  gneisses  and 
granites.  If  this  is  the  case,  the  statement  is  true,  for  these  materials 
are  seen  in  sharp  contact  at  very  numerous  places  along  the  Animas. 
If  these  hornblende- schists  and  gneisses  are  altered  erupt  ives,  as  they 
appear  to  be,  the  sharp  contacts  would  have  no  bearing  upon  the  meta- 
morphic  origin  of  the  granite. 
Some  of  the  quartzites  have  a  color  similar  to  the  coarse  reddish  or 
grayish  gneisses,  and  also  show  to  some  extent  a  banded  appearance. 
It  may  be  that  this  fact  has  led  to  the  statement  that  there  is  a  transi- 
tion between  them  and  the  granitic  rocks. 
A  study  of  numerous  thin  sections  of  the  material  collected  shows 
that  the  rocks  composing  the  area  here  called  granitic  are  always 
completely  crystalline,  giving  in  the  thin  section  no  evidence  whatever 
of  clastic  characters ;  on  the  other  hand,  all  the  rocks  belonging  in  the 
quartzite  area,  while  locally  considerably  altered  by  dynamic  action, 
show  very  clearly  their  clastic  character.  However,  the  evidence  of  the 
microscope  is  not  necessary  to  show  the  clastic  origin  of  these  quartz- 
ites, as  the  conglomeratic  phases  seen  in  the  field  are  sufficient  to 
demonstrate  this. 
As  to  the  conformability  described  by  Endlich  between  the  flat-lying 
Devonian  and  these  crystalline  rocks,  no  observations  were  made.  It 
is,  however,  to  be  remarked  that  Endlich  states  that  the  crystallines 
are  flat-lying,  having  a  dip  of  not  more  than  10°  to  15°.  This  was 
observed  to  be  the  case  in  one  locality,  but  as  before  said,  the  great 
Bull.  86 21 
