van  .use. j  LAKE    SUPERIOR    REGION.  183 
tipper  Vermilion,  Upper  Kaministiqnia,  etc.  To  the  writer  there  seem 
grave  difficulties,  based  on  general  relations,  in  the  way  of  accepting 
this  conclusion.  On  the  other  hand,  the  Upper  Kaministiqnia  conglom- 
erates, not  far  distant  from  the  ordinary  phases  of  the  Anirnikie  rocks, 
have  a  decidedly  different  appearance.  This  may,  however,  he  due  to 
the  fact  that  certain  of  these  conglomerates  are  of  volcanic  origin,  the 
chert  and  jasper  of  which  appear  to  have  been  broken  from  their  beds 
by  volcanic  action  and  mingled  with  lava  and  volcanic  ash.  This  sudden 
change  in  the  character  of  the  beds  of  the  same  age  is  parallelized  in  the 
Penokee  district,  where  the  strata,  within  a  distance  of  a  few  miles,  rapidly 
change  in  character,  become  immensely  thick,  and  are  largely  in  the 
nature  of  agglomerates,  greenstone  conglomerates,  etc.  But  it  must  be 
said  that  such  detailed  mapping  has  not  been  done  adjacent  to  the 
National  boundary  of  northeastern  Minnesota  and  Ontario  and  in  the 
Thunder  bay  district  as  will  warrant  any  positive  statement  as  to 
whether  within  the  clastic  series,  between  the  base  of  the  Keweenawan 
and  the  Basement  Complex,  there  is  another  higher  physical  break, 
making  two  unconformities  which  separate  the  rocks  into  three  series. 
The  ore,  chert  and  jasper  conglomerates  used  as  evidence  of  physical 
breaks  within  the  clastic  series  are  not  to  be  confounded  with  the 
purely  volcanic  conglomerates  which  may  occur  at  any  horizon.  Also 
the  occurrence  of  these  conglomerates  will  have  no  such  meaning  as  here 
assigned  by  those  who  believe  that  the  ore,  chert  and  jasper  in  their 
present  condition  are  igneous  rocks.  To  such  they  will  be  no  more  evi- 
dence of  two  series  than  that  the  Keweenawan  conglomerates,  the  frag- 
ments of  which  are  derived  from  contemporaneous  traps,  are  evidence 
of  many  series.  But  to  those  who  think  the  evidence  is  sufficient  for 
the  belief  that  the  ore,  chert  and  jasper  are  not  only  sedimentary  rocks, 
but  sedimentary  rocks  which  have  gone  through  a  long  and  complex 
history,  the  evidence  of  a  physical  break  furnished  by  these  conglomer- 
ates will  be  satisfactory. 
correlation;  general  considerations. 
We  pass  now  to  the  general  correlation  of  the  lake  Superior  forma- 
tion lying  between  the  two  planes  already  defined,  the  base  of  the 
Keweenawan  and  the  top  of  the  Archean  schist- gneiss- granite  complex. 
Before  it  can  be  decided  whether  series  so  far  distant  from  each 
other  as  the  Dakota  quartzites  and  the  Original  Huronian  (separated 
by  800  miles)  can  be  parallelized,  it  ought  to  be  more  definitely  sett  led 
to  what  extent  correlation  can  be  made  by  unconformities  and  lithologi- 
cal  likenesses,  Irving  inclined  to  the  belief  that  such  structural  breaks 
as  that  described  in  the  Marquette  district  are  of  great  extent,  and  this 
accords  with  the  general  trend  of  modern  structural  work.  From  what 
has  gone  before  it  appears  exceedingly  probable  that  the  structural 
break  between  the  Upper  and  Lower  Marquette  is  identical  with  that 
