318  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
nominee,  the  cherty  limestone  formation  of  the  Penokee  district,  and 
also  probably  the  Kaministiquia  series  of  Ontario  and  the  Black  Kiver 
Falls  series  of  Wisconsin. 
The  formations  of  the  Upper  Hnronian  are  (1)  a  basement  slate 
and  quartzite,  frequently  bearing  basal  conglomerates;  (2)  an  iron- 
bearing  formation,  consisting  originally  of  lean  cherty  carbonate  of 
iron,  calcium,  and  magnesium,  and  (3)  an  upper  slate..  Associated 
with  the  sedimentaries  in  the  Miehigamme,  Crystal  Falls,  and  other 
districts  are  great  volcanic  series,  comprising  greenstones,  agglom- 
erates, greenstone  conglomerates,  volcanic  ash,  and  amygdaloids. 
Where  these  occur  the  orderly  succession  is  destroyed.  Included  in 
the  Upper  Hnronian  are  the  Penokee,  Mesabi,  Animikie,  Upper  Mar- 
quette, Upper  Menominee,  and  Upper  Felch  Mountain  districts. 
The  Keweenawan  consists  of  interstratified  lavas,  sandstones,  and 
conglomerates.  The  lavas  are  prevalent  at  the  lower  part  of  the 
series,  interstratifications  of  the  two  occur  in  the  middle  portions, 
and  the  pure  detritals  exclude  the  volcanics  in  the  upper  portion  of 
the  series. 
The  Lower  Huronian  is  largely  crystalline,  the  Upper  Hnronian 
semicrystalline,  and  the  KeAveenawan  simply  cemented.  Locally, 
along  axes  of  intense  plication,  both  the  Lower  Huronian  and  the 
Upper  Huronian  have  been  transformed  into  completely  crystalline 
schists.  The  Cambrian  of  Lake  Superior  is  a  horizontal  sandstone, 
and  rests  unconformable  upon  all  the  preceding. 
Winchell  (N.  H.)  ,330  in  1895,  reviews  the  stratigraphy  of  the  Lake 
Superior  region.  In  reference  to  the  Keweenawan  series  he  reaches 
the  following  conclusions:  (1)  The  eruptive  rocks  which  in  Michigan, 
Wisconsin,  and  Minnesota  have  been  included  in  the  Keweenawan 
consist  of  two  widely  differing  series  of  widely  separated  ages.  In- 
cluded in  these  pre-Keweenawan  eruptives  are  the  great  gabbro  of 
Minnesota  and  the  red  rocks  such  as  those  at  the  Palisades  and  at 
Pigeon  Point.  This  eruptive  period  is.  called  the  Animikie  revolu- 
tion. (2)  This  period  was  followed  by  a  long  erosion  interval,  dur- 
ing which  were  deposited  the  Sioux  quartzites  of  Dakota,  the  New 
Ulm  quartzites  of  Minnesota,  the  Baraboo  and  Barron  quartzites  of 
Wisconsin,  and  the  quartzites  and  conglomerates  below  the  Keweena- 
wan diabases  in  the  Penokee  district.  In  the  New  Ulm  quartzites  are 
found  "  taconite  "  jasper  pebbles,  and  these  are  taken  as  evidence 
that  this  material  was  derived  from  the  Animikie.  (3)  Following 
this  conglomerate  and  quartzite  is  the  Keweenawan  eruptive  age, 
which  separates  the  Paradoxides  horizon  from  the  Dicellocephalus 
horizon.  (4)  The  Olenellus  horizon  is  separated  from  the  Paradox- 
ides horizon  by  the  disturbance  that  closed  the  Animikie. 
