3MM0NS.]         COPPER    IN    RED    BEDS    OF    COLORADO    PLATEAU.  227 
In  all  the  above  instances  no  near-by  occurrence  of  igneous  rocks  is 
loted  by  the  respective  authors,  though  their  absence  is  not  explicitly 
stated,  except  by  Turner. 
To  the  northwest  of  the  San  Juan  Mountains  in  Colorado  extends 
;he  flat,  slightly  dome-shaped  uplift  of  the  Uncompahgre  Plateau, 
formed,  as  shown  by  the  deeper  canyon  cuts,  by  Mesozoic  rocks,  at 
he  base  of  which  the  Triassic  red  sandstones  rest  directly  upon 
granite  and  schist. 
On  the  south  side  of  this  uplift  Carboniferous  beds  are  interposed 
)etween  the  Mesozoic  and  Archean,  while  just  across  the  Colorado 
)oundary  in  Utah  projecting  points  of  a  laccolith  breaking  through 
he  Cretaceous  beds  form  the  Sierra  La  Sal. 
Copper  ores  of  economic  value  having  been  reported  in  this  region, 
[  made,  in  the  summer  of  1899,  a  reconnaissance  examination  of  some 
>f  the  deposits  in  the  Unaweap  Valley,  which  is  a  deep  cut  across  the 
Jncompahgre  uplift  about  15  miles  south  of  Grand  Junction,  Colo. 
[  found  here  a  series  of  distinct  fault  fissures  crossing  red  sandstones, 
vhich  in  some  cases  could  be  traced  down  into  the  underlying  granite 
exposed  in  the  valley  bottom.  Some  of  the  lower  beds  of  the  sand- 
itones  are  quite  calcareous,  passing  into  a  deep  red,  impure  limestone, 
rhe  vein  fissures  are  a  few  feet  wide  and  carry  fragments  of  the  red 
imestone  even  well  down  into  the  granite.  The  ore  is  largely 
;halcocite  and  bornite,  with  some  carbonates,  resulting  from  the 
i Iteration  of  chalcopyrite,  in  a  gangue  of  quartz  and  calcite  with  occa- 
ional  fluorspar.  It  is  said  to  carry  values  in  gold  and  silver.  The 
Principal  accumulations  of  ore  occur  where  the  fissures  cross  the  calca- 
eous  beds  near  the  base  of  the  red  sandstones.  Here  it  spreads  out  for 
i  considerable  distance  laterally,  while  above  and  below  the  metallic 
ninerals  decrease  in  quantity.  In  one  tunnel  in  the  granite,  which 
:ollows  the  vein  for  about  300  feet,  only  occasional  small  specks  of 
opper  ore  were  seen.  From  the  observations  made  during  this  visit 
he  vein  materials  might  equally  well  have  been  assumed  to  have  been 
►rought  up  from  below  by  waters  ascending  along  the  fissures,  or  to 
»e  the  concentration  by  circulating  waters  of  materials  originally 
[isseminated  throughout  the  sedimentary  beds. 
In  the  same  summer  Messrs.  F.  L.  Ransome  and  A.  C.  Spencer 
lade  a  reconnaissance  through  the  country  farther  south  from 
^elluride  westward  to  Paradox  and  Sinbad  valleys  in  order  to  study 
le  occurence  of  uranium,  vanadium,  and  copper  ores.  All  these 
res  were  found  as  impregnations  of  the  lighter  colored  sandstones 
immediately  overlying  the  "  Red  Beds  "  or  Dolores  formation.  They 
re,  however,  not   universally  or  uniformly   distributed,   but   occur 
here  there  are  some  disturbances,  mainly  a  faulting  or  Assuring  of 
ie  beds.     The  copper  impregnations  in  the  sandstones  are  usually 
