v\n  msR.i  LAKE    SUPERIOR    REGION.  185 
tbe  strongest  evidence  is  brought  forward  is  on  the  outskirts  of  the 
Original  Huronian,  and  a  part  of  the  formation  which  Logan  and  Mur- 
ray have  mapped  as  Lower  Slate  conglomerate  is  placed  by  Winchell  as 
Upper  Slate  conglomerate.  The  observations  of  Pumpelly  and  myseli 
at  a  contact  between  the  limestone  formation  and  the  Upper  Slate  con- 
glomerate tend  to  confirm  WinchelPs  conclusion,  but  since  limestone 
fragments  are  plentiful  in  the  Upper  Slate  conglomerate,  we  place  the 
physical  break  just  above  this  lower  limestone,  i.  e.,  300  feet  higher 
than  indicated  by  Winchell. 
The  term  Original  Huronian  as  here  used  is  strictly  confined  to  the 
areas  first  described  by  Logan  and  Murray  on  the  north  shore  of  lake 
Huron,  and  in  1863  mapped  in  detail.  The  Original  Huronian  only  is 
here  compared  with  the  series  about  lake  Superior  because  it  is  the 
area  to  which  the  term  was  first  applied,  and  also  because  it  has  been 
more  thoroughly  described  and  mapped  than  any  other  area  in  Canada 
designated  by  the  term  Huronian.  A  careful  field  and  laboratory  study 
of  the  rocks  of  the  Original  Huronian  has  shown  its  upper  series  to  con- 
sist in  great  part  (1)  of  fragmental  quartzites,  the  induration  of  which 
has  been  caused  by  deposition  of  interstitial  silica;  (2)  of  graywackes 
and  graywacke  slates  (often  conglomeratic — Logan's  Upper  Slate  con- 
glomerate), the  induration  of  which  is  due  to  the  deposition  of  intersti- 
tial silica  and  metasomatic  changes  in  the  feldspar;  (3)  of  cherty  lime- 
stones, and  (I)  of  eruptives.  The  Lower  Huronian  series  is  more  meta- 
morphosed than  the  Upper. 
In  its  readily  recognized  fragmental  character  and  in  its  gentle  fold- 
ing the  upper  Original  Huronian  series,  i.  e.,  the  upper  13,000  feet,  is 
closely  analogous  to  thePenokee,  Upper  Marquette,  and  Animikie,  while 
the  Lower  Huronian  may  be  compared  with  the  Lower  Marquette  and 
Lower  Vermilion  iron  bearing  series.  In  the  order  of  succession  of 
formations  it  can  not  be  said  that  either  series  corresponds  very 
closely  with  the  series  about  lake  Superior,  to  which  they  are  com- 
pared. 
It  seems  to  us  that  in  correlation  the  unmetamorphosed  character  of 
the  Upper  Huronian  is  a  guide  of  some  importance.  As  pointed  out  by 
McKellar,  the  intense  folding  to  which  the  Vermilion  lake  and  Kami- 
nistiquia  series  have  been  subjected  must  have  preceded  the  much 
more  gentle  synclinal  movement  which  formed  the  basin  of  lake  Snpe 
rior.  That  no  violent  dynamic  movement  has  occurred  since  the  begin- 
ning of  Animikie  time  is  known  to  be  true  of  the  lake  Superior  basin, 
and  it  seems  exceedingly  probable  that  the  gently  folded  upper  mem- 
bers of  lake  Huron  belong  with  those  of  like  character  about  lake 
Superior.  If  this  is  not  the  case,  the  intense  dynamic  movements 
which  produced  the  closely  folded  rocks  of  northeastern  Minnesota  and 
Ontario  lost  their  force  before  reaching  the  area  about  lake  Huron,  and 
this\  "egion  must  have  escaped  any  serious  folding  for  a  longer  time  than 
auyl  »ther  closely  studied  part  of  the  earth's  crust. 
