172  PRE-CAMBRIAN    GEOLOGY   OF    NORTH   AMERICA. 
where  it  appears  at  the  Loretto  mine  and  eastward.  The  second  im- 
portant area  of  Vulcan  iron  formation  stretches  off  about  5  miles 
along  the  south  side  of  the  central  dolomite  belt  running  north  of 
Lakes  Antoine  and  Fumee,  and  ending  somewhere  about  the  east 
line  of  R.  30  W.  At  the  east  end  of  the  dolomite  area  the  iron-bearing 
formation  appears  in  the  lean  slates  at  Iron  Hill.  The  third  stretch 
of  country  in  which  the  iron-bearing  beds  are  to  be  expected  is  that 
which  borders  the  northern  dolomite  belt,  but  while  pits  have  shown 
the  existence  of  the  formation  here  its  distribution  is  unknown.  The 
other  areas  in  which  the  Vulcan  formation  may  occur  are  those 
bordering  the  Quinnesec  schists,  but  this  has  not  yet  been  determined. 
The  Traders  member  consists  of  ferruginous  conglomerate,  ferru- 
ginous quartzite,  heavily  ferruginous  quartzose  slates,  and  iron-ore 
deposits.  The  Brier  member  consists  of  heavy  black  ferruginous  and 
quartzose  slates.  The  Curry  member  consists  of  interbedded  jaspil- 
ite,  ferruginous  quartzose  slates,  and  iron-ore  deposits.  The  rela- 
tions of  the  Traders  and  Brier  Hill  members  where  there  has  been  no 
disturbance  of  the  strata  are  those  of  gradation.  Where  there  has 
been  disturbance,  as  in  the  vicinity  of  Norway,  there  has  been  a  zone 
of  differential  movement  between  the  two,  resulting  in  slickensides 
and  brecciated  zones.  Between  the  Brier  slates  and  the  Curry  mem- 
ber there  is  gradation. 
The  Vulcan  formation  is  bent  into  folds  of  several  orders  of  magni- 
tude, the  greater  ones  corresponding  approximately  to  the  folds 
in  the  underlying  Randville  dolomite.  The  total  thickness  of  the 
formation  is  probably  GOO  to  700  feet. 
The  iron-ore  deposits  of  large  size  rest  upon  relatively  impervious 
formations,  which  are  in  such  position  as  to  constitute  pitching 
troughs.  A  pitching  trough  may  be  made  (a)  by  the  dolomite  forma- 
tion underlying  the  Traders  member  of  the  Vulcan  formation,  (b) 
by  a  slate  constituting  the  lower  part  of  the  Traders  member,  and  (c) 
by  the  Brier  slate  between  the  Traders  and  Curry  members  of  the 
Vulcan  formation.  The  dolomite  formation  is  especially  likely  to 
furnish  an  impervious  basement  where  its  upper  horizon  has  been 
transformed  into  a  talc  schist,  as  a  consequence  of  folding  and  shear- 
ing between  the  formations. 
Unconformably  above  the  Vulcan  iron  formation  is  the  Hanbury 
formation,  which  forms  three  large  belts  in  the  syncline  of  the  older 
rocks,  and  occupies  a  very  large  proportion  of  the  district.  The  for- 
mation comprises  clay  slates,  calcareous  slates,  graphite  slates,  gray- 
wackes,  quartzite,  ferruginous  dolomite,  and  rare  bodies  of  ferrugi- 
nous chert  and  iron  oxide.  The  formation  is  much  thicker  than  any 
of  the  other  formations  of  the  district,  but  its  thickness  is  probably 
not  more  than  2,000  or  3,000  feet. 
