322  PRE-CAMBRIAN   ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
number  of  observations  along  the  Animas  show  the  dips  to  be  for  the 
most  part  very  high,  i.  e.,  from  60°  to  vertically,  and  in  various  direc- 
tions. All  of  the  evidence  as  to  the  strike  and  dip  show  that  the  area 
of  quartzites  and  granites  is  one  in  which  the  folding  is  very  compli- 
cated. 
Bearing  upon  the  question  of  the  position  of  the  quartzitic  series 
with  reference  to  the  fossiliferous  rocks  is  the  occurrence  south  of 
Ouray,  along  Eed  mountain  creek  and  one  of  the  branches  of  the  TJn- 
compahgre,  of  a  great  series  of  slates,  quartzites  and  conglomerates, 
with  high  dips  and  repeated  by  folding,  which  are  in  lithological  char- 
acter identical  with  the  quartzites  south  of  Silverton.  Just  south  of 
Ouray  the  red  beds  of  the  Jura-Trias  are  found  in  almost  horizontal 
j)osition  upon  the  upturned  edges  of  the  slates  and  quartzites.  This 
unconformity,  in  the  distance  at  which  it  may  be  observed  and  in 
the  masses  of  rocks  exposed,  is  remarkably  handsome.  Conformable 
below  the  red  beds  of  the  Jura-Trias,  at  Ouray,  the  Carboniferous 
rocks  appear,  but  they  were  not  seen  in  contact  with  the  slates 
and  quartzites.  That  the  quartzite  series  was  an  old  shore  against 
which  the  Carboniferous  and  Jura- Trias  were  deposited  can  not  be 
doubted.  In  the  distance  of  about  5  miles  in  which  this  quartzite 
series  is  exposed  a  slate  band  is  found  five  times.  In  going  north  the 
dips  are  first  south  and  then  change  to  the  north,  in  which  position 
they  continue  until  the  Carboniferous  appears.  All  this  suggests  that 
we  have  here  to  deal  with  a  folded  series  and  not  one  necessarily  of 
very  great  thickness,  although  probably  several  thousand  feet  thick. 
As  Ouray  is  only  a  few  miles  from  Silverton,  the  argument  of  analogy 
makes  it  probable  that  the  similar  plainly  rragmental  slates  and  quartz- 
ites south  of  Ouray  are  the  equivalent  of  the  quartzites  of  Elk  park. 
The  facts  bear  against  the  probability  of  a  transition  from  the  Devonian 
into  the  quartzitic  series  of  the  latter  place.  The  one  occurrence  in 
which  this  transition  is  definitely  asserted  is  perhaps  a  case  of  a  recoin- 
posed  rock  resting  upon  a  crystalline  one.  Similar  occurrences  have 
often  been  described. 
As  to  the  relations  of  the  granitic  area  to  the  quartzites  along  the 
Animas,  there  is  no  clear  evidence.  The  fact  that  the  granitic  area 
is  an  intricate  complex  of  regularly  banded  gneisses,  of  granitoid 
gneiss,  and  of  granites  cut  by  hornblende- schists  in  dike-like  forms, 
combined  with  the  fact  that  no  such  dike-like  areas  are  found  near 
the  quartzites,  seems  to  indicate  that  the  quartzite  is  of  later  age  than 
this  complex.  This  probability  is  still  further  strengthened  by  the 
completely  crystalline  character  of  one  series  and  the  plainly  frag- 
mental  character  of  the  other.  This  point  would  have  little  weight  if 
the  granitic  area  was  a  simple  massive  rock  which  might  be  the  result 
of  a  single  eruption.  But  the  varieties  of  rock  of  which  it  is  composed 
and  the  intricate  way  in  which  these  lithological  phases  are  mingled 
indicate  that  the  history  of  the  granite  area  is  a  most  complex  and 
