GRAY   IRON    ORES    OF    TALLADEGA    <  OUNTY,  ALA.  175 
In  places,  however,  the  relative  percentage  of  magnetite  so  increases 
that  the  ore  becomes  somewhat  magnetic. 
When  exposed  to  weathering  the  ore  takes  on  a  rather  ashy  gray 
color,  and  the  name  gray  ore  therefore  not  only  describes  it,  bul 
serves  to  distinguish  it  from  the  red  or  the  brown  ores  of  northern 
Alabama.  As  the  ore  is  a  variable  mixture  of  magnetite  and  hema- 
tite the  simple  term  gray  ore  is  sufficiently  distinctive  and  yet  implies 
no  definite  limitation  of  the  iron  mineral. 
Thin  sections  of  the  ore  contain,  in  addition  to  the  iron  minerals,  a 
great  deal  of  quartz,  which  is  the  main  source  of  the  silica  content. 
There  is  some  feldspar,  mainly  soda-lime  feldspar,  although  there 
is  also  some  microcline.  Mica  as  a  secondary  product  is  represented 
by  scattered  blades  of  muscovite.  Biotite  is  practically  absent. 
Some  chlorite,  secondary  after  mica,  is  found,  but  it  is  not  abundant. 
The  main  constituents  of  the  ore  are  quartz  and  iron.  The  hematite 
is  in  scaly  and  apparently  sheared  aggregates,  while  the  magnetite 
is  generally  in  well-formed,  sharp  crystals,  which  have  apparently 
been  formed  later  than  the  hematite.  In  a  very  few  thin  sections 
iron  sulphide  has  been  recognized.  The  quartz  occurs  in  two  dis- 
tinct forms — as  an  original  mineral,  very  much  strained  and  shat- 
tered, and  as  a  secondary  mineral,  showing  no  optical  stress.  This 
secondary  quartz  includes  many  crystals  of  magnetite,  the  relations 
of  these  minerals  showing  the  relative  age  of  crystallization  of  the 
magnetite  and  the  later  quartz.  Mica  was  apparently  contempo- 
raneous with  the  later  quartz.  The  magnetite,  the  later  quartz, 
and  the  mica  were  probably  formed  at  the  close  of  the  period  of 
dynamic  metamorphism  during  which  the  mountains  were  built. 
The  accompanying  chemical  analyses  bring  out  more  clearly  the  char- 
acter of  the  ores  of  this  district.  Table  I  comprises  analyses  that  have 
already  been  published.  Table  II  comprises  unpublished  analyses, 
most  of  which  have  been  collected  from  mining  or  prospecting  com- 
panies, and  are  less  complete  than  those  in  Table  I.  Table  III  also 
consists  of  analyses  hitherto  unpublished,  but  these  were  made 
from  material  collected  by  the  United  States  Geological  Survey. 
The  analyses  in  Table  III  should  therefore  receive  greater  weight 
than  those  in  either  of  the  other  two  tables,  for  the  samples  were  taken 
carefully  and  the  personal  equation  was  eliminated  as  far  as  possible. 
Samples  procured  by  interested  parties  are  generally  misleading, 
for  they  are  not  usually  taken  across  the  entire  width  of  the  vein 
which  is  to  be  mined.  It  is  practically  impossible  to  select  one 
fragment  of  rock  which  shall  represent  the  true  value  of  a  vein; 
therefore  some  method  of  sampling  which  shall  be  entirely  impartial 
must  be  adopted.  The  samples  from  which  all  the  analyses  shown 
in  Table  III  were  made  were  taken  by  cutting  a  continuous  groove 
the  entire  width  of  the  vein  and  preserving  all  the  chips  from  the 
