228  CONTRIBUTIONS    TO   ECONOMIC    GEOLOGY,  1904.        [bull.  260. 
spherical  concretions  or  nodules,  blue  or  green  in  color,  averaging 
about  the  size  of  a  pea,  while  the  uranium  mineral,  carnotite,  is  yellow 
and  forms  streaks  running  generally  parallel  to  the  bedding.  Vein 
deposits  of  copper  ore  were  also  found,  Avhere  the  veins  are  fault 
fissures,  generally  of  slight  displacement,  carrying  crushed  sand- 
stone and  calcite,  with  argentiferous  chalcocite  and  some  copper  car- 
bonates. The  latter  impregnate  the  sandstone  country  rock  in  specks, 
and  sometimes  color  the  entire  bed  green  to  a  distance  of  100  feet  or 
more  from  the  vein.  The  distance  over  which  the  uranium  minerals 
were  observed  by  Ransome  and  Spencer  is  in  round  numbers  about 
100  miles,  and  similar  occurrences  have  been  reported,  since  the 
recent  excitement  over  radium-bearing  minerals,  another  hundred 
miles  farther  west,  in  the  region  known  as  the  San  Raphael  Swell,  in 
Utah,  which  probably  occur  at  the  same  horizon  and  in  similar 
conditions  with  those  noted  in  Colorado.  In  all  these  cases  there  are 
no  igneous  rocks  in  the  immediate  vicinity  of  the  deposit. 
It  may  be  well  to  mention  here  the  Silver  Reef  deposits,  not  far 
from  the  town  of  St.  George,  in  southern  Utah,  which  lies  on  the 
western  border  of  the  Plateau  region.  Their  origin  was  the  subject  of; 
very  lively  discussion  some  twenty -odd  years  ago.  They  occur  pre- 
sumably at  about  the  same  horizon  as  those  already  mentioned — 
namely,  in  the  light-colored  sandstones  immediately  overlying  the 
"  Red  Beds."  The  ores  consist  of  impregnations  of  these  sandstones 
by  chloride  of  silver,  which  is  associated  with  and  often  replaces 
plant  remains.  Copper  ores,  mostly  carbonates,  also  occur  in  the 
same  beds,  though  in  subordinate  quantities. 
Newberry  maintained  that  these  ores  were  deposited  contemporane- 
ously with  the  sandstones,  but  the  majority  of  other  observers  held  to 
the  view  that  the  metals  were  subsequently  introduced,  basing  their 
opinion  upon  their  apparent  connection  with  the  disturbed  and  frac- 
tured condition  of  the  rocks  and  upon  the  occurrence  of  igneous 
rocks  in  the  vicinity.  Not  having  visited  the  locality,  I  hesitate  to 
form  an  opinion  as  to  the  probability  of  either  theory. 
Mr.  H.  F.  Lunt  has  recently  published  a  a  short  notice  of  copper' 
ores  occurring  at  the  same  horizon.  These  occur  on  the  east  side  oil 
the  Colorado  River,  about  125  miles  north  of  Flagstaff,  in  the  white 
Mesa  sandstone  which  immediately  overlies  the  Triassic  "  Red  Beds.'! 
They  consist,  according  to  Mr.  Lunt,  of  the  replacement  of  the  cement 
of  a  particular  stratum  of  cross-bedded  sandstone  by  chrysocollai 
with  some  tenorite,  some  specimens  of  which  contain  up  to  32  per  cenl 
of  copper.  The  ore  is  apparently  associated  with  small  vertica 
crevices,  and  sometimes  shows  vein  structure,  though  it  generall} 
grades  off  rather  indefinitely  into  the  white  sandstone. 
•  Trans.  Am.  Inst.  Min,  Eng.,  vol,  34,  p.  989. 
