344  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         '[  rill.  LM50. 
dioxide  left  no  ground  for  calling  the  material  a  "  ferrous  carbon- 
ate," and  the  presence  of  so  large  an  amount  of  iron  as  claimed  was 
entirely  inconsistent  with  its  light  weight. 
Mr.  Roberts  very  kindly  arranged  to  conduct  Mr.  W.  J.  Sutton,  of 
Victoria,  British  Columbia,  and  myself  to  the  locality  that  we  might 
study  this  material  in  place.  We  took  the  Oregon  Railway  and 
Navigation  Company's  railroad  to  Bridal  Veil  Falls  on  the  Columbia 
River,  28  miles  east  of  Portland,  then  walked  back  on  the  railroad 
about  2J  miles  to  near  Rooster  Rock,  where  the  "  ore  "  occurs  in  great 
abundance,  forming  prominent  cliffs  500  feet  in  height  overlooking 
the  railroad  and  river. 
The  whole  mass  of  the  cliffs  when  seen  from  the  railroad  is  more  or 
less  distinctly  stratified,  but  the  layers  are  large  and  massive,  so  that 
the  stratification  is  not  conspicuous.  When  examined  in  detail  the 
strata  are  found  to  be  made  up  entirely  of  fragmental  volcanic  ma- 
terial, forming  what  is  technically  called  tuff,  or,  in  this  case,  basalt 
tuff,  on  account  of  the  basaltic  character  of  the  fragments.  Such 
material  is  sometimes  called  palagonite  tuff,  from  its  occurrence  in 
Palagonia,  Sicily. 
The  layers  are  composed  chiefly  and  often  wholly  of  a  substance 
ranging  in  color  from  light  to  dark  brown  and  black,  and  in  luster 
from  dull  glassy  to  pitch  like  and  resinous.  For  the  most  part  the 
rock  is  decidedly  fragmental.  It  contains  fragments  of  dark  basalt 
from  the  size  of  a  pea  to  blocks  several  feet  in  diameter.  When 
broken,  these  pieces  are  often  seen  to  have  a  black  pitchy  border,  as 
if  once  enveloped  by  a  molten  mass. 
Weathering  brings  out  the  fragmental  structure  on  the  surface  of 
the  glassy  portions,  but  this  is  still  more  evident  in  a  thin  section  of 
the  rock  where  the  dark  brown  completely  isothropic  glass  frag- 
ments full  of  small  lath-shaped  crystals  of  plagioclase  feldspar,  with 
fewer  crystals  of  augite  and  grains  of  olivine,  like  those  of  the  basalt, 
are  encompassed  and  bound  together  by  a  lighter  brown  matrix  like 
gelatin,  which  has  fibrous  polarization. 
Locally  among  the  distinctly  fragmental  layers  are  sheets  of  the 
yellowish-brown  waxv-lustered  material  which  in  thin  section  is 
found  to  be  an  altered  jellylike  substance  containing  crystal  frag- 
ments of  plagioclase,  augite,  and  olivine  like  those  in  the  basalt  of 
the  large  fragments  and  flows  in  the  cliffs,  and  it  is  evident  that  the 
whole  mass  is  from  a  volcano  erupting  basalt.  Some  of  it  flowed  out, 
but  most  of  it  was  blown  out  by  violent  explosive  eruption,  giving  it 
a  wide  distribution  about  the  volcano. 
In  order  to  determine  the  amount  of  iron  contained  in  the  basalt 
tuff,  I  collected  a  number  of  samples  in  the  field.  Recognizing  the 
character  of  the  material,  I  selected  for  the  principal  sample  to  be 
