220  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
Low,46  in  1886,  reports  on  the  Mistassini  expedition.  The  Laurentian 
gneisses  and  associated  rocks  occupy  the  whole  country  from  the  gulf 
of  St.  Lawrence  to  James  bay,  along  the  route  traversed,  with  the  excep- 
tion of  some  areas  of  Huronian  and  Cambrian  in  the  vicinity  of  lake 
Mistassini.  The  Laurentian  rocks  include  gneiss,  hornblende- schists, 
mica-schists,  crystalline  limestones,  and  areas  of  triclinic  feldspar  rocks. 
The  rocks  described  by  Richardson,  north  of  lake  Abatagomaw,  are  sim- 
ilar to  the  epidotic  and  chloritic  slates  of  the  Shickshock  mountains  and 
the  eastern  townships  and  are  referred  to  the  Huronian. 
SUMMARY   OF   RESULTS. 
In  the  very  brief  and  general  studies  of  the  area  north  of  the  lower 
St.  Lawrence  no  attempt  is  made  to  map  the  region  in  detail  nor  to 
work  out  the  structure  of  the  rocks.  The  Labradorite  rocks  are  sepa- 
rated by  Eichardson  from  the  gneissoid  rocks,  to  which  he  applies  the 
term  Laurentian.  The  reason  for  doing  this  is  not  given,  so  that  we 
have  no  indication  as  to  whether  this  is  an  eruptive  or  a  sedimentary 
series,  and  if  sedimentary,  whether  it  underlies  or  overlies  the  gneisses, 
As  iu  the  Ottawa  region,  the  great  mass  of  gneiss  is  free  from  lime- 
stones. The  limestones  are  local  and  are  associated  with  other  rocks 
which  are  presumably  of  clastic  origin,  such  as  quartzites. 
The  remarks  which  are  made  with  reference  to  two  series  in  the 
Ottawa  area  would  apply  equally  well  to  this  region.  We  have  no  in- 
dication as  to  the  relations  of  the  clastic  series,  described  by  Eichard- 
son, to  the  Laurentian  gneiss  which  is  referred  by  Low  to  the  Huronian. 
Eichardson,  who  did  the  work  upon  this  series,  was  not  able  to  give  an 
opinion  as  to  its  position,  and  its  reference  to  the  Huronian  by  Low  is 
made  wholly  upon  lithological  grounds.  It  is,  however,  probable  that 
the  great  conglomerates  in  the  neighborhood  of  Lake  Abatagomaw,  com- 
posed almost  entirely  of  rounded  fragments  of  Laurentian  gneiss  and 
which  in  some  places  closely  resemble  the  gneiss,  mark  the  structural 
boundary  between  the  two  series  of  rocks.  The  description  of  this  con- 
glomerate is  that  of  a  recomposed  rock,  the  material  being  derived  from 
the  immediately  underlying  formation. 
NOTES. 
1  Report  on  an  Exploration  in  1875  between  James  bay  and  lakes  Superior  and 
Huron,  Robert  Bell.  Rept.  of  Prog.  Geol.  Survey  of  Canada  for  1875-'76,  pp.  294-342. 
*  2  Report  on  an  Exploration  of  the  East  Coast  of  Hudson  Bay,  Robert  Bell.  Rept. 
of  Prog,  of  Geol.  Survey  of  Canada  for  1877-78,  pp.  1-37  C.     With  a  map. 
3  Report  on  the  country  between  Lake  Winnipeg  and  Hudson's  Bay,  Robert  Bell. 
Ibid.,  pp.  1-31  CC.     With  5  plates  and  2  maps. 
4  Report  on  Explorations  of  the  Churchill  and  Nelson  Rivers,  and  around  God's 
and  Island  Lakes,  Robert  Bell.  Rept.  of  Prog.  Geol.  Survey  of  Canada  for  1878-79, 
pp.  1-44  C.     With  a  map. 
6  Report  on  Hudson  Bay  and  some  of  the  Lakes  and  Rivers  lyiug  to  the  west  oi 
it,  Robert  Bell.     Rept.  of  Prog.  Geol.  Survey  of  Canada  for  1879-'80,  pp.  1-56  C. 
6  Report  on  the  Geology  of  the  Basin  of  Moose  River  and  adjacent  country,  Robert 
