384  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
In  the  Gogebic  district  the  unconformity  at  the  base  of  the  Ani- 
mikie  was  recognized  by  the  early  geologists,  and  particularly  by 
Brooks.  The  underlying  rocks  were  referred  to  a  "  Laurentian " 
complex.  Irving,  in  his  Wisconsin  Geological  Survey  work,  referred 
to  the  underlying  cherty  limestone  as  a  peculiar  phase  of  quartzite  at 
the  base  of  the  Animikie.  The  work  of  Van  Hise  leading  to  the  pub- 
lication of  Monograph  XIX  of  the  United  States  Geological  Survey 
proved,  by  evidence  at  many  points  along  the  range,  the  existence  of 
an  unconformity  between  the  Animikie  and  this  limestone  and  under- 
lying rocks. 
UNCONFORMITY   BENEATH   THE  HURONIAN   SERIES. 
Bell  and  Selwyn  find  no  evidence  of  discordance  between  their 
"Laurentian  "  and  "  Huronian."  Bell,  in  1873,  says  the  distinction 
between  the  "  Laurentian "  and  "  Huronian  "  is  chiefly  of  a  litho- 
logical  character,  while  Selwyn,  in  1883,  states  that  he  can  give  no 
better  reason  for  supposing  that  certain  sets  of  beds  belong  to  the 
"  Laurentian  "  and  others  to  the  "  Huronian  "  than  a  considerable 
difference  in  lithological  character,  the  former  being  essentially  gran- 
itoid, gneissic,  and  feldspathic,  while  the  latter  is  quartzose,  horn- 
blendic,  schistose,  and  slaty. 
Dawson  (Sir  William),  Logan,  and  Bell  all  mention  granite  and 
gneiss  fragments  in  the  original  Huronian  east  of  Lake  Superior, 
and  Logan  clearly  believed  the  two  to  be  unconformable.  Irving 
found  additional  evidence  in  favor  of  this  unconformity.  Work  of 
Pumpelly  and  Van  Hise  has  shown  that  the  lowest  member  of  the 
original  Huronian,  as  mapped  by  Logan,  rests  with  a  great  uncon- 
formity upon  the  basement  complex,  the  "  Laurentian  "  of  Logan. 
Selwyn,  although  thinking  the  "Huronian  "  and  "  Laurentian  "  con- 
formable, states  that  "  Laurentian  "  pebbles  occur  in  the  "  Huronian." 
In  the  Lake  of  the  Woods  and  Rainy  Lake  districts  Lawson  failed 
to  recognize  the  unconformity  between  the  "  Huronian  "  and  the  un- 
derlying basal  complex,  now  recognized  in  that  district  by  the  joint 
committee ;  indeed,  he  believed  the  "  Huronian  "  (his  "  Coutchiching  ") 
to  lie  below  the  basal  greenstones  (his  Keewatin).  Pumpelly  and 
Smyth  differ  from  Lawson  in  that  they  find  a  great  structural  dis- 
cordance between  the  basal  clastic  series  east  of  Rainy  Lake  and  a 
fundamental  complex  consisting  of  granite,  gneiss,  and  schist,  while 
finding  the  superinduced  foliation  of  both  series  parallel. 
In  Minnesota  the  Winchells,  although  recognizing  the  plane  be- 
tween the  elastics  and  crystallines  as  a  boundary  between  two  series 
of  rocks,  maintain  conformity  and  gradations,  although  Alexander 
Winchell  suggests  the  possibility  that  the  apparent  conformity  is 
superinduced  by  subsequent  dynamic  action.     Van  Hise  and  Irving 
