442  PRE-CAMBRIAN   GEOLOGY   OF   NORTH   AMERICA. 
and  metamorphism  to  the  middle  and  lower  Huronian  underlying 
what  is  here  regarded  as  the  equivalent  of  the  Animikie  group  in  the 
Marquette  district  of  Michigan,  and  are  accordingly  correlated  with 
them.  On  the  same  basis  the  lower  Huronian  may  be  correlated  with 
the  cherty  limestone  and  quartzite  of  the  lower  Huronian  of  the 
Gogebic  district  and  with  the  Randville  dolomite  and  Sturgeon 
quartzite  of  the  Crystal  Falls  and  Menominee  districts.  In  the 
Minnesota  districts  there  is  nothing  in  the  lithological  character  of  the 
sedimentary  group  beneath  the  Animikie  and  above  the  Archean  to 
indicate  whether  it  should  be  correlated  with  the  lower  Huronian  or 
with  the  middle  Huronian  or  partly  with  each.  The  basis  for  their 
correlation  with  the  Huronian  is  simply  their  occurrence  in  a  similar 
general  succession  between  the  Archean  and  the  Animikie. 
The  Huronian  series  rests  unconformably  on  the  Archean  system, 
composed  of  the  Keewatin  and  Laurentian  series,  which  are  corre- 
lated with  the  Keewatin  and  Laurentian  of  the  Lake  Superior  region. 
This  unconformity  is  the  same  as  that  designated  "  inter-Huronian  " 
by  certain  of  the  Canadian  geologists  who  have  applied  the  term 
"  Lower  Huronian  "  to  the  Keewatin  rocks. 
The  succession  and  nomenclature  of  Logan  and  Murray,  later  Ca- 
nadian geologists,  and  United  States  geologists  are  summarized  in 
the  following  table : 
