234  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bui.t,  86.   \ 
nian  system.  The  passage  from  division  2  to  division  3,  that  is,  from  the  1 
Laurentian  to  the  Huronian,  is  a  gradual  one,  as  the  two  groups  are  I 
intimately  associated. 
Placing  the  Upper  Coldbrook  group  as  pre- Silurian,  the  unconform- 1 
ability  of  this  group  with  the  Silurian  is  marked  in  general.  The  Pri- 1 
mordial  beds  sometimes  rest  upon  division  3  and  sometimes  upon  division  1 
4,  they  contain  in  places  coarse  basal  conglomerates,  and  appear  to  have  1 
been  originally  deposited  among  the  hollows  of  the  Huronian  series.! 
South  of  Bloomsbury  mountain,  and  on  the  main  stream  of  Black  river  j 
and  the  adjacent  region,  the  Huronian  rocks  are  associated  with  the  I 
Devonian,  and  the  two  formations  accord  almost  exactly  both  in  strike! 
and  dip,  the  Devonian  being  included  among  the  Huronian  rocks.  But  I 
in  addition  to  the  fact  that  the  conglomerates  of  the  former  are  largely! 
made  up  of  the  debris  of  the  latter,  there  are  points  in  which  this  ac-l 
cordance  is  clearly  wanting.  The  discordance  is  pretty  well  seen  at  the  J 
east  branch  of  Black  river. 
Matthew,38  in  1879,  finds  the  Kingston  series  to  exhibit  a  strong 
resemblance  to  the  Huronian  formation  of  St.  John  county,  but  it  is  re- 
garded as  Silurian  on  paieontological  grounds. 
Bailey,  Matthew,  and  Ells,39  in  1880,  give  a  general  review  of 
their  work  done  upon  southern  New  Brunswick,  which  covers  an  area 
of  about  6,000  square  miles.     The  rocks  comprised  under  the  pre-Cam- 
brian  include  the  Laurentian  of  1871  and  the  three  former  divisions  of 
the  Huronian-Coastal,  Coldbrook,  and  Kingston.     Of  the  relations  of 
the  upper  members  of  the  Laurentian  mica-schist,  limestone,  and  fine 
gneiss,  to  the  main  body  of  coarse  syenite  and  syenitic  gneiss  constitut- 
ing the  Lower  Laurentian,  nothing  further  is  known  than  contained  in 
the  report  of  1870-'71.     The  greatly  broken  and  disturbed  character  of 
the  supposed  upper  series,  the  obscure  stratification  of  much  of  the 
underlying  group,  and  the  frequent  occurrence  of  intrusive  masses, 
combine  to  make  the  determination  difficult.    There  can,  however,  be. 
no  question  that  the  bulk  of  the  calcareous  and  siliceous  strata  are  more 
recent  than  the  coarse  granitoid  rocks  with  which  they  are  associated.? 
With  one  possible  exception,  no  instances  of  direct  superposition  of  the 
Coldbrook  rocks  on  the  Laurentian   have  been  observed  j   but  the| 
Coastal  rocks  are  found  upon  the  Coldbrook  rocks  as  well  as  upon  the  I 
Upper  Laurentian,  so  there  is  no  reasonable  doubt  as  to  the  true  sue- 1 
cession.     Contacts  of  the  Coastal  group  with  the  Coldbrook  group  are 
found  in  the  county  of  St.  John,  and  especially  along  the  line  of  the  St.! 
Martins  and  IJpham  railway,  between  Upliani  and  Quaco,  and  on  the  v 
lower  Quaco  road  on  either  side  of  Bloomsbury  mountain.     In  passing! 
from  one  to  the  other  there  is  often  an  abrupt  change  of  dip,  the  beds  I 
of  the  higher  series  dipping  at  a  lower  angle  than  those  upon  which 
they  rest,  while  along  the  same  line  of  contact  it  is  not  uncommon  to* 
find  masses  of  coarse  breccia  conglomerate,  in  which  the  fragments  are 
hugely  the  petrosilex  derived  from  the  inferior  group.     It  is,  however,  I 
