weki»]  NOTES    ON    THE    COPPER   MINES    OF    VERMONT.  191 
blende,  presumably  meaning  amphibolite.  Their  course  and  that  of 
the  granite  intrusions  suggests  a  deep-seated  batholitic  mass.  In  this 
report  the  schist  is  separated  into  two  formations — the  Washington 
marble  and  the  Bradford  schist.  The  copper  deposits  occur  only  in 
the  micaceous  rocks  grouped  under  the  latter  name.  These  rocks  are 
concealed  over  large  areas  by  the  bowlders  and  gravels  of  the  glacial 
moraines,  so  that  while  good  exposures  occur  near  the  mines  the  rocks 
can  not  be  continuously  traced  from  one  locality  to  another.  The 
published  structure  sections  indicate  folding,  but  the  distribution  of 
the  rocks  appears  to  suggest  extensive  faulting  as  well. 
The  schistose  rocks  of  the  region,  which  underlie  the  glacial  drift 
and  frequently  project  through  it,  are  prevailingly  slate  colored  or 
gray,  varying  from  coarse  to  fine  in  texture  and  foliation,  the  differ- 
ences in  color  being  due  to  varying  proportions  of  biotite  and  silica. 
At  the  Elizabeth  mine  the  foliation  is  very  regular  and  the  bands  can 
be  traced  for  long  distances,  although  the  exposures  are  not  always 
satisfactory.  At  Copperfield  the  general  foliation  is  north  and  south, 
with  a  dip  of  25°  to  30°  E.,  but  the  structure  is  in  general  that  of  a 
broad  anticlinal  fold,  the  detailed  structure  showing  close  folding  and 
puckering  of  the  softer,  more  schistose  beds,  so  that  no  single  band 
can  be  followed  for  a  long  distance.  The  rocks  when  so  folded  con- 
tain many  intercalated  masses  of  quartz,  occupying  the  crests  of  the 
little  anticlines  and  filling  irregular  lenticular  spaces  along  the  flanks 
of  the  folds.  The  origin  of  this  quartz  is  believed  to  be  associated 
with  the  alteration  of  the  original  rocks  to  their  present  sericitic  con- 
dition. As  shown  elsewhere,  the  change  of  ordinary  silicates  to  the 
fine  talc-like  form  of  muscovite-mica,  known  as  sericite,  is  accompanied 
by  the  liberation  of  free  silica,  which  is  carried  to  the  nearest  cavity 
and  accumulates  as  quartz.  Examinations  of  thin  sections  of  these 
rocks  under  the  microscope  shows  them  to  consist  of  quartz,  biotite, 
calcite,  and  magnetite.  They  thus  appear  to  represent  metamorphosed 
sedimentary  rocks,  probabty  impure  sandstones,  and  siliceous  shales. 
A  detailed  study  of  all  the  granite  intrusions  of  this  part  of  the 
State  has  never  been  made,  but  a  recent  examination  and  study  of  the 
Barre  granite  mass,  which  is  extensively  quarried,  has  been  made  by 
Mr.  G.  I.  Finlay,  under  the  direction  of  Professor  Kemp,  of  Columbia 
University. a 
This  Barre  mass  lies  due  north  of  the  copper  belt,  but  many  out- 
lying bosses  of  it  extend  southward  in  a  line  west  of  the  copper  belt. 
The  rock  at  Barre  is  of  fairly  uniform  composition  as  a  whole,  but 
shows  various  border  fades,  a  feature  also  found  in  a  minor  degree  in 
the  smaller  masses  to  the  south.  The  rock  is  a  normal  quartz-bio tite- 
granite,  containing  accessory  muscovite  and  apatite.  The  intrusion 
occurs  associated  with  dikes  of  pegmatitic  granite,  which,  according 
o  Finlay,  G.  I.,  The  granite  area  of  Barre,  Vermont:  Rept.  State  Geologist  Vermont  for  1901-2,  p.  46. 
