vanuise.]  LAKE    HURON    TO    LAKE    TEMISCAMANG.  47 
nian  was  Irving,  who  in  1887  clearly  showed  that  such  an  unconformity 
occurs.    The  observations  of  Pumpelly  and  myself  reenforce  this  con 
elusion  and  show  that  between  the  lowest  member  of  the  Huronian  and 
Laurentian  complex  is  a  very  great  discordance. 
The  facts  given  by  Barlow,  taken  in  connection  with  the  foregoing, 
show  that  he  Las  neglected  to  differentiate  the  clastic  rocks  of  the 
Huronian,  from  the  more  ancient  underlying  crystalline  gneisses.  Also, 
he  has  failed  to  separate  an  earlier  granite-gneiss  from  a  later  intrusive. 
That  a  part  of  the  granite  is  eruptive,  of  later  age  than  the  Huronian, 
was  as  well  known  to  Logan  and  Murray  as  to  Barlow.  These  early 
geologists  recognized  both  a  later  granite  and  a  granite-gneiss  basement 
complex  upon  which  the  Huronian  was  deposited,  while  the  latter 
failed  to  make  this  fundamental  discrimination.  He  saw  the  former 
and  assumed  that  this  covered  the  entire  ground. 
As  to  the  position  taken  by  Alexander  Winchell,  that  the  Original 
Huronian  is  divisible  into  two  unconformable  series,  it  may  be 
remarked  that  the  locality  in  which  the  strongest  evidence  for  this  is 
given,  Echo  lake,  is  on  the  outskirts  of  the  area  mapped  in  detail  by 
Logan  and  Murray.  Before  accepting  the  conclusion  that  these  geolo- 
gists, in  their  careful  work  extending  over  several  years  in  the  area  of 
the  Original  Huronian,  have  overlooked  a  great  unconformity  and  have 
misunderstood  what  part  of  the  area  is  covered  by  lower  slate  con- 
glomerate and  what  by  upper  slate  conglomerate,  we  ought  to  have  the 
most  decisive  evidence.  However,  the  observations  of  Pumpelly  and 
myself  tend  toward  the  correctness  of  Winchell's  first  conclusion.  At 
least  between  the  limestone  and  the  upper  slate  conglomerate,  in  places, 
there  has  been  a  considerable  erosion  interval.  That  with  the  Huronian 
in  the  more  general  work  of  later  years  Logan  and  Murray  placed  two 
discordant  series  is  certain.  The  same  was  done  by  the  geologists  on 
the  south  shore  of  lake  Superior,  and  in  view  of  this  very  common  ref- 
erence it  is  stated  in  another  place  that  for  these  two  series  the  terms 
Upper  Huronian  and  Lower  Huronian  are  used.  If  it  is  really  the  case 
that  in  the  Original  Huronian  of  the  north  channel  of  lake  Huron,  in 
the  area  covered  by  the  detailed  map  of  1863,  two  discordant  series  do 
exist3  this  suggestion  is  eminently  appropriate. 
Great  indisputable  results  were  reached  by  the  early  Canadian 
geologists,  Logan  and  Murray.  This  district  north  of  lake  Huron  was 
the  first  in  which  it  was  shown  that  an  unmistakable  detrital  and 
little  metamorphosed  series  of  rocks  rests  unconformably  under  the 
upper  Cambrian.  Also  it  was  shown  that  this  series  is  of  such  a  char- 
acter that  the  ordinary  stratigraphical  methods  apply,  and  Logan  and 
Murray  were  able  to  subdivide  it  into  formations  upon  a  lithological 
basis  in  the  same  fashion  as  is  done  in  fossiliferous  series.  This  is  so 
evident  that  it  would  not  be  emphasized  if  it  had  not  been  denied. 
Far  more  to  the  credit  of  Logan  and  Murray  is  the  recognition  of  the 
character  of  the  amygdaloids  and  the  interbedded  greenstones,  ^o 
extreme  metamorphic  theory  was  applied  to  them,  and  they  were  dis- 
