52  CONTRIBUTIONS    TO   ECONOMIC    GEOLOGY,  1904.        [bull.  260. 
the  upper  massive  portion  being  particularly  well  exposed  in  Box 
Canyon  of  Canyon  Creek  and  in  the  vicinity  of  the  Mineral  Farm 
mine. 
The  Molas  formation,  consisting  of  50  feet  of  red  shales  and  chert 
conglomerates,  rests  uncomfortably  on  the  Ouray  limestones  and  is 
followed  by  about  1,400  feet  of  the  Hermosa  formation.  The  beds 
are  of  Pennsylvanian  ("  Upper  Carboniferous")  age.  The  Hermosa 
consists  of  fossiliferous  limestones,  sandstones,  and  shales  in  the  lower 
part,  while  thick  massive  sandstones  and  grits  of  a  pink  or  reddish 
color  predominate  above.  These  are  the  rocks  that  form  the  prom- 
inent cliffs  about  the  mouth  of  Oak  Creek,  directly  west  of  town. 
The  Hermosa  is  followed  by  1,500  feet  or  more  of  Permian  red 
beds,  called  the  Cutler  formation,  consisting  of  coarse  conglomer- 
ates, sandstones,  and  shales,  all  of  a  bright-red  color.  They  were 
sharply  folded  and  their  upturned  edges  beveled  off  by  erosion 
before  the  Triassic  Dolores  formation  was  deposited,  so  that  in  the 
immediate  vicinity  of  Oura\r  they  are  poorly  represented.  They  are 
best  seen  4  or  5  miles  north  of  Ouray,  in  the  neighborhood  of  Dexter 
and  Cutler  creeks. 
The  Dolores  formation  consists  of  about  100  feet  of  bright  red 
sandstones  and  shales,  with  a  very  characteristic  conglomerate  con- 
taining limestone  pebbles  at  the  base.  The  unconformable  relations 
of  the  Dolores  to  the  underlying  beds  is  well  shown  in  the  cliffs  east 
of  Ouray,  between  Portland  and  Cascade  creeks,  where  the  Triassic 
beds  have  transgressed  the  Cutler  formation  and  rest  upon  the  Her- 
mosa. 
The  four  other  Mesozoic  formations  that  occur  in  this  area — the  La 
Plata,  McElmo,  Dakota,  and  Mancos — are  of  particular  interest  be- 
cause it  is  with  them  that  the  more  important  ore  deposits  are  asso- 
ciated. In  areas  where  they  have  not  been  metamorphosed  by  intru- 
sions of  igneous  rocks  they  are  easily  recognized  by  their  lithologic 
characteristics,  but  in  the  neighborhood  of  the  American  Nettie  and 
Bachelor  mines  they  have  been  deformed  to  some  extent  and  altered  I 
by  intrusive  porpl^ries  so  that  they  can  not  always  be  readily  dis- 
tinguished. 
The  La  Plata  formation,  immediately  above  the  Dolores,  consists 
of  two  massive  light-yellow  or  almost  Avhite  sandstones  separated  by 
a  peculiar  silicified  breccia  of  limestone  and  calcareous  shale.  The 
whole  formation  is  100  feet  thick.  This  is  followed  by  TOO  or  800 
feet  of  thin  greenish  and  reddish  shales  and  sandstones,  with  some 
more  massive  sandstones  near  the  base.  This  is  the  McElmo  forma- 
tion, which  in  the  vicinity  of  Bridal  Veil  and  "  Blowout  "  creeks  has. 
together  with  the  red  Dolores,  been  bleached,  and  many  of  the  sand- 
stone members  have  been  converted  into  quartzites.  The  La  Plata  | 
and  McElmo  are  of  Jurassic  age. 
