collier.]       TIN    DEPOSITS    OF    THE    YORK    REGION,    ALASKA.  163 
intrusive  igneous  rock,  either  of  the  greenstone  or  of  the  granite  type. 
Some  bowlders  and  pebbles  of  greenstone  occurring  in  the  gravels  of 
Buck  Creek  near  its  mouth  have  not  been  traced  to  their  source,  but 
probably  came  from  a  group  of  greenstone  hills  on  the  south  of  Grouse 
Creek. 
Small  quartz  veins  were  found  in  a  number  of  places  along  Buck 
Creek,  cutting  both  across  the  bedding  of  the  slates  and  running 
parallel  with  it.  Some  of  these  quartz  veins  are  3  or  4  feet  wide,  and 
one  or  two  of  them  can  be  traced  for  a  quarter  of  a  mile  or  farther. 
Most  of  the  veins  are  mere  stringers  1  or  2  inches  thick  and  only  a 
few  feet  long.  At  one  place  on  the  upper  part  of  the  creek  a  vein  of 
nearly  pure  pyrite  6  or  8  feet  wide  was  seen.  Pebbles  of  pyrite  2  or 
3  inches  in  diameter,  oxidized  on  the  outside  to  limonite,  are  found  in 
the  gravels  below  this  vein. 
Mr.  Edgar  Rickard,  in  the  Engineering  and  Mining  Journal  for  Jan- 
uary 3,  1903, a  reports  that  the  source  of  the  cassiterite  can  be  readily 
found  in  the  slate  of  the  Potato  Mountain  range,  where  it  undoubtedly 
occurs  in  countless  small  veins  and  vugs,  sometimes  associated  with 
quartz  scattered  through  the  mass  of  slate.  The  action  of  the  elements 
has  worn  away  the  slates,  leaving  the  cassiterite  on  the  hillsides,  and 
the  streams  have  concentrated  it  into  appreciable  deposits. 
Though  specimens  obtained  from  the  gravel  justify  this  conclusion, 
no  veins  of  this  kind  were  seen  by  Mr.  Hess  nor  by  any  of  the  con- 
siderable number  of  prospectors  who  were  actually  engaged  in  the 
search  for  veins  containing  tin. 
The  gravel  deposits  in  the  bed  of  Buck  Creek  are  ordinarily  from 
100  to  150  feet  wide,  varying  greatly  in  different  parts  of  the  creek. 
Excepting  a  few  greenstone  bowlders  found  below  the  mouth  of  Sutter 
Creek,  the}r  consist  of  slate  and  quartz,  together  with  other  minerals 
derived  from  the  country  rock,  such  as  hematite,  limonite,  magnetite, 
ilmenite,  pyrite,  cassiterite,  and  a  small  amount  of  gold.  Cassiterite 
in  the  form  of  stream  tin  is  distributed  from  the  mouth  of  the  creek 
to  within  a  mile  of  its  head,  above  which  point  little  more  than  traces 
have  been  found.  The  ore  varies  in  size  from  fine  sand  to  pebbles 
weighing  13  or  11  pounds.  Several  pieces  from  5  to  8  pounds  in 
weight  were  seen  by  Mr.  Hess,  though  the  average  size  is  much  smaller. 
A  few  of  the  pebbles  are  perfectly  rounded,  but  most  of  them  are  sub- 
angular.  The  ore  from  the  workings  near  the  mouth  of  Buck  Creek 
is  generally  well  rounded,  while  that  from  near  the  head  is  sharp  and 
angular.  In  general,  the  farther  up  the  creek  it  is  obtained  the  more 
angular  is  the  ore.  In  color  the  ore  varies  from  black  to  light  resin 
or  amber.  All  that  has  been  seen  makes  a  light-colored  resinous 
powder,  by  which  it  is  readily  distinguished  from  hematite  or  other 
« Rickard,  Edgar,  Tin  deposits  of  the  York  region,  Alaska:  Eng.  and  Min.  Jour.,  vol.  75,  p.  30. 
