36  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
the  veins  pass  in  some  cases  from  granite  or  gneiss  into  and  through  a  porphyry  dike  and 
continue  uninterrupted  into  granite  or  gneiss  on  the  other  side. 
Placer  deposits. — The  first  discovery  of  pay  gold  in  Clear  Creek  County,  and  one  of  the 
first  in  Colorado,  was  made  by  George  Jackson  about  the  1st  of  April,  1859,"  on  Chicago 
Creek,  just  above  its  junction  with  Clear  Creek. 
This  is  considered  by  many  to  have  been  the  first  discovery  of  gold  in  Colorado,  but, 
according  to  Hollister,  B.  F.  Langley  had,  about  the  end  of  the  preceding  January,  found 
placer  deposits  in  a  gulch  on  South  Boulder  Creek.  These  deposits,  which  were  known  as 
"Deadwood  Diggings,"  had  by  the  end  of  March  produced  considerable  gold  and  were 
affording  employment  to  quite  a  number  of  men.  Small  amounts  of  gold  had  also  previ- 
ously been  encountered  near  Golden,  and  on  Ralston  Creek,  a  small  tributary  of  Clear  Creek. 
On  Clear  Creek  placer  mining  was  prosecuted  from  Grass  Valley  Bar,  3  miles  below 
the  mouth  of  Chicago  Creek,  to  the  forks  of  the  South  Branch,  some  9  miles  above  this  same 
point. 
By  the  end  of  May,  1859,  there  were  nearly  300  men  employed  at  "Jackson  Diggings" 
and  on  the  various  claims  for  several  miles  up  and  down  Clear  Creek  from  this  point.  These 
deposits  yielded  good  returns  to  some  of  the  workers  for  a  great  many  years;  in  fact,  the 
yield  of  the  precious  metals  in  Colorado  previous  to  1864  was  almost  entirely  derived  from 
these  placers  and  from  the  sluicing  of  the  decomposed  surface  ores  of  the  veins,  for  the  silver 
mines  were  not  operated  until  1865,  and  the  unaltered  gold-bearing  sulphides  could  not  be 
treated  with  profit.  The  placers  were  most  profitably  worked  between  the  years  1859  and 
1863. 
The  placer  gold  deposits  of  Clear  Creek  County  may  be  classed  as  (1)  river-bar  placers, 
(2)  stream  placers,  and  (3)  bench  placers.  The  river-bar  deposits  are  those  on  gravel  flats 
in  or  adjacent  to  the  beds  of  the  streams.  The  stream  deposits  consist  of  the  deposits  of 
bowlders,  gravel,  and  sand  filling  the  channels  and  forming  the  beds  of  the  streams.  The 
bench  placers  are  ancient  stream  deposits  which  are  at  present  represented  by  remnants  of 
old  stream  terraces  located  at  a  considerable  elevation  above  the  level  of  the  present  water 
courses.  There  are  three  conspicuous  lines  of  terraces.  While  not  of  glacial  origin,  the 
lowest  of  these,  which  is  about  25  feet  above  the  present  stream  beds,  consists  largely  of 
glacial  material  which  has  been  worked  over  and  transported  to  its  present  position  by 
streams  subsequent  to  the  period  of  glaciation.  The  second  gravel  terrace,  which,  according 
to  Mr.  S.  H.  Ball,  is  possibly  pre-Glacial  in  origin,  is  found  55  feet  above  the  creek  bed.  The 
third  set  of  terraces  is  180  feet  above  the  channels  of  the  present  streams  ;-,nd  consists 
often  of  indurated  river  gravels  of  late  Tertiary  or  early  Pleistocene  age. 
The  principal  deposits  along  Clear  Creek  occur  in  the  vicinity  of  Idaho  Springs  and  extend 
from  the  junction  of  Fall  River  and  Clear  Creek  to  the  forks,  several  miles  below  the  town, 
where  North  Clear  Creek,  which  flows  through  Blackhawk,  joins  the  main  stream. 
"Jackson  Diggings,"  where  the  first  discovery  of  gold  in  the  county  was  made  by  George 
Jackson  in  April,  1859,  is  located  on  Chicago  Creek  near  its  junction  with  Clear  Creek.  The 
exact  site  where  Jackson  first  found  gold  is  said  to  be  beneath  a  large  willow  tree  on  the 
road  north  of  Chicago  Creek,  about  halfway  between  the  Jackson  and  Waltham  concen- 
trating mills;  this  site  is  now  included  in  what,  is  known  as  the  "Edwards  Placer."  The 
material  at  "Jackson  Diggings"  consisted  of  coarse  gravel  and  sand,  occurring  as  bars  oi 
flats  in  or  adjacent  to  the  streams,  and  of  deposits  forming  the  stream  bed  itself.  The  low 
benches  along  the  sides  and  in  places  on  top  of  the  low  ridge  or  spur  of  land  which  separates 
Chicago  Creek  from  Clear  Creek  just  above  their  union  were  also  worked  extensively.  Much 
of  this  material  was  sluiced  at  very  large  profits  in  the  early  days.  The  deposits  of  Spanish 
Bar,  which  was  the  name  given  to  the  portion  of  Clear  Creek  extending  from  the  junctior 
of  Fall  River  and  Clear  Creek  to  a  point  below  the  Stanley  mine,  consisted  mainly  of  a  mas; 
of  bowlders  of  all  sizes,  gravel,  and  sand,  filling  the  channel  of  the  stream,  which  here  rum 
in  a  comparatively  narrow  valley. 
allollister,  The  Mines  of  Colorado,  1867,  p. 
