414  PRE-CAMBRIAN    GEOLOGY   OF    NORTH   AMERICA. 
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  2  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  imme- 
diately subjacent  granite.  The  evidence  of  erosive  unconformability 
is  thus  of  the  clearest  character.  The  likeness  of  the  slate  conglom- 
erate 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 
of  this  slate  conglomerate  as  the  lower  one,  and,  if  it  is,  the  uncon- 
formable contact  is  between  the  lower  series  of  the  Huronian  and  the 
granite. 
At  the  contact  between  the  lower  quartzite  of  Logan  and  the  Lau- 
rentian east  of  Thessalon,  described  by  Irving,  it  Avas  found  that  the 
relations  could  be  much  more  clearly  seen  than  at  the  time  the  locality 
was  visited  by  Irving,  because  then  the  water  was  very  high  and  two 
islands  upon  which  the  contact  occurs  were  submerged.  The  Lauren- 
tian area  does  not  consist  of  simply  granite  or  gneiss,  as  might  be  in- 
ferred 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  waterworn  appearance.  However,  in  any 
given  area  the  fragments  are  always  of  material  identical  with  that 
of  the  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  character  from  the  pseudo-conglomerates  of  the 
Laurentian.  The  pebbles  and  bowlders  instead  of  being  widely  sepa- 
rated are  packed  closely  together.  Within  a  very  small  area,  a 
square  yard  or  square  rod,  may  be  found  all  varieties  of  the  material 
occurring  within  the  Basement  Complex — that  is,  many  phases  of 
crystalline  schist,  gneiss,  granite,  and  granite  gneiss.  On  one  of  the 
islands  in  which  the  contact  was  seen  the  line  of  separation  is  per- 
fectly sharp  and  irregular,  bending  at  one  place  at  an  angle  of  50°. 
Also  the  foliation  of  the  granite  gneisses  abuts  almost  at  right  angles 
against  the  line  of  contact  at  one  place.  The  contact  here,  then,  has 
all  the  characteristics  of  one  of  erosive  unconformability.  Upon  the 
second  island,  instead  of  a  clear  line  of  contact  between  the  conglom- 
erate and  the  Basement  Complex,  there  is  an  apparent  gradation,  the 
