vanhise.]  LAKE    HURON   TO    LAKE    TEMISCAMANG.  45 
Winchell's  conclusion  that  the  Laurentian  is  divisible  into-two  dis- 
cordant series,  the  break  occurring  above  the  lower  limestone.  If  this 
break  shall  prove  to  be  general  at  this  horizon,  it  places  in  the  Lower 
Huronian,  using  Logan's  thicknesses  for  the  formations,  about  5,000 
feet,  and  in  the  Upper  Huronian  about  13,000  feet. 
Almost  immediately  below  the  limestone  was  found  the  lower  slate 
conglomerate,  which  in  lithological  character  is  precisely  like  the  slate 
conglomerate  in  contact  with  the  granite  below  described. 
As  bearing  upon  the  relations  of  the  Huronian  and  Laurentian,  one 
new  locality  was  found,  and  the  contact  described  by  Irving  east  of 
Thessalon  was  again  examined.  About  two  miles  northwest  of  Garden 
river  the  lower  slate  conglomerate  of  Logan  was  traced  downward  into 
a  finely  laminated  semicrystalline  quartzose  schist,  and  this  downward 
into  a  basal  conglomerate  and  recomposed  granite  which  rests  almost 
directly  upon  the  solid  granite.  The  major  part  of  the  debris  of  the 
basal  bowlder  conglomerate  is  derived  from  the  immediately  subjacent 
granite.  The  evidence  of  erosive  unconforinability  is  thus  of  the  clear- 
est character.  The  likeness  of  the  slate  conglomerate  at  this  locality 
to  that  below  the  limestone,  the  metamorphosed  character  of  the 
quartzose  schist  and  the  steepness  of  the  inclination  of  the  rocks  all 
bear  toward  the  correctness  of  Logan's  mapping,  that  this  slate  con- 
glomerate is  the  lower  one,  and,  if  so,  the  unconformable  contact  is 
between  the  lower  series  of  the  Huronian  and  the  granite. 
At  the  contact  between  the  lower  quartzite  of  Logan  and  the  Lauren- 
tian east  of  Thessalon,  described  by  Irving,  it  was  found  that  the 
relations  could  be  much  more  clearly  seen  than  at  the  time  the  locality 
was  visited  by  Irving,  because  the  water  was  very  low,  and  two  islands 
upon  which  the  contact  occurs  were  then  submerged.  The  Laurentian 
area  does  not  consist  of  simply  granite  or  gneiss,  as  might  be  inferred 
from  Logan's  mapping,  but  is  an  intricate  complex  of  granite,  gneiss,  and 
schist.  The  granite  has  intruded  the  schist  and  fine  grained  gneisses  in 
the  most  intricate  manner.  In  many  places  large  roundish  fragments 
of  schist  or  gneiss  are  contained  in  granite,  and  these  have  a  decidedly 
water-worn  appearance.  However,  in  any  given  area  the  fragments 
are  always  of  material  identical  with  that  of  the  immediate  adjacent 
gneiss  or  schist.  In  short,  the  rocks  furnish  one  of  the  most  beautiful 
illustrations  of  the  relations  described  by  Lawson  between  schists  and 
gneisses  and  a  later  intrusive  granite.  Resting  upon  this  complex 
was  found  a  great  bowlder  conglomerate  which  differs  radically  in 
its  character  from  the  pseudo-conglomerates  of  the  Laurentian.  The 
pebbles  and  bowlders  instead  of  being  widely  separated  are  packed 
closely  together.  Within  a  very  small  area,  a  square  yard  or  square 
rod,  may  be  found  all  varieties  of  the  material  to  be  found  within  the 
basement  complex:  that  is,  many  phases  of  crystalline  schist,  gneiss, 
granite,  and  granite  gneiss.  On  one  of  the  islands  in  which  the  Con1  act 
was  seen,  the  line  of  separation  is  perfectly  sharp  and  irregular,  bend- 
