820  PRE-CAMBRIAN    GEOLOGY   OF    NORTH    AMERICA. 
Comstock,"  in  1887,  describes  the  metamorphic  series  in  southwest- 
ern Colorado  as  probably  Silurian  or  Devonian.  This  series  is  sus- 
ceptible of  division  into  an  upper  or  granitic  division  and  an  under- 
lying quartzitic  formation.  The  quartzitic  group  is  exposed  in  the 
Animas  Canyon  below  Silverton,  forming  a  line  of  jagged  peaks  to 
the  eastward,  the  Xeedle  Mountains.  Whenever  the  quartzite  is  well 
uncovered  the  more  recent  granites  are  usually  traceable  along  the 
flanks  of  the  belt.  The  geological  map  brings  out  no  apparent  system 
in  the  metamorphic  rocks. 
Lakes,100  in  1889,  describes,  on  the  Mears  road,  south  of  Ouray,  as 
succeeding  the  Carboniferous  limestone,  a  thickness  of  13,000  feet  of 
distinctly  stratified  and  hard  vitreous  quartzites,  slates,  and  schists. 
Part  of  these  may  belong  to  the  Silurian  and  Cambrian,  but  as  these 
combined  rarely  attain  in  Colorado  a  thickness  of  1,000  feet,  so  great 
a  body  is  extraordinary  and  suggests  that  the  lower  part  of  it  may,  as 
in  Canada,  belong  to  the  Huronian  or  Laurentian,  upper  divisions  of 
the  Archean  not  elsewhere  represented  in  Colorado.  The  dip  of  the 
quartzite  is  about  75°  N.  The  uplifted  crests  have  been  deeply 
eroded  and  in  the  hollows  so  formed  rest  the  masshre  volcanic  breccias. 
Van  Hise,38  in  1889,  made  observations  along  the  Animas,  the  rail- 
road being  followed  from  below  Needleton  to  Silverton,  a  distance 
of  about  17  or  18  miles.  As  mapped  by  Endlich  on  Sheet  XV  of  the 
Atlas  of  Colorado,  this  course  is  situated,  with  the  exception  of  5  or  0 
miles,  in  the  quartzite  area.  Quartzites  occur  for  a  little  more  than 
2  miles  in  the  vicinity  of  Elk  Park,  in  the  middle  of  the  area  mapped 
as  quartzite.  The  granitic  area  was  found  to  be  a  most  intricate  com- 
plex of  massive  granite,  coarse  and  fine,  white  and  black  banded 
gneiss,  and  black  hornblende  schist  or  gneiss  in  dikelike  forms.  The 
strikes  and  dips  vary  greatly,  although  for  the  most  part  they  are 
high,  running  from  75°  to  85°.  At  one  place  the  dip  of  the  schistose 
structure  wTas  observed  to  be  as  flat  as  10°  or  15°. 
On  neither  side  of  the  quartzite  area  was  evidence  seen  of  a  transi- 
tion into  granite;  nor  were  the  quartzites  and  granites  seen  in  contact; 
they  were  found,  however,  a  few  paces  apart.  At  the  southern  bound- 
ary, 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  syn- 
clines  of  quartzites  which  are  adjacent  to  the  granite. 
Bearing  upon  the  question  of  the  position  of  the  quartzitic  series 
with  reference  to  the  fossiliferous  rocks  is  the  occurrence  south  of 
Ouray,  along  Red  Mountain  Creek  and  one  of  the  branches  of  the 
Uncompahgre,  of  a  great  series  of  slates,  quartzites,  and  conglomer- 
ates, with  high  dips  and  repeated  by  folding,  which  are  in  lithological 
character  identical  with  the  quartzites  south  of  Silverton.  Just  south 
of  Ouray  the  shales  and  limestones  of  the  Devonian  are  found  in 
