NEW    BKUNSWICK,    NOVA.  SCOTIA,    NEWFOUNDLAND,    ETC.      491 
consists  principally  of  granite,  gneiss,  mica  schist,  and  thick  beds  of 
crystalline  limestone.  This  is  the  Laurentian  or  Portland  group. 
Resting  upon  the  Portland  group  is  the  Colclbrook  group,  belonging 
to  the  Huronian  division  of  the  Azoic  system,  also  thick  deposits  of 
altered  slate  of  a  volcanic  character,  surmounted  by  conglomerates. 
The  Coldbrook  group  is  succeeded  by  the  St.  John  group,  which  con- 
tains no  coarse  material  and  is  regarded  as  equivalent  to  the  Potsdam 
or  Primordial  of  New  York.  Above  the  St.  John  group  is  the 
Bloomsbury  group,  of  volcanic  character,  such  as  basalt,  amygdaloid, 
and  trap  rock,  which  are  associated  with  conglomerates  and  slates 
destitute  of  fossils.  Geographically  separated  from  the  above  groups 
are  the  rocks  of  Kingston,  which  are  regarded  as  Upper  Silurian, 
and  the  mica  schists  of  Queens  County,  which  may  be  Cambrian. 
Scattered  through  all  the  above  are  igneous  rocks,  such  as  granite, 
syenite,  porphyry  and  trap,  which  may  occur  associated  with  rocks 
of  any  age.  The  Portland  group  is  in  almost  entire  conformity  with 
the  Coldbrook  group.  The  lithological  resemblance  of  the  Cold- 
brook  group  (7,000  feet  thick)  with  the  Huronian  is  very  close.  The 
presence  of  graphite  in  the  Portland  and  St.  John  groups  is  regarded 
as  evidence  of  life. 
The  extreme  metamorphism  of  the  Portland  group  is  evidence  of  its 
great  antiquity.  This  age  would  never  have  been  doubted  were  it  not 
for  the  intimate  association  and  conformity  with  the  beds  of  the  over- 
lying groups,  which  are  unquestionably  Upper  Devonian,  and  the 
Portland  was  supposed  to  represent  either  a  portion  of  the  Lower 
Devonian  or  possibly  the  upper  part  of  the  Silurian.  During  the 
deposition  of  the  Azoic  and  Silurian  ages  a  long  period  of  repose  pre- 
vailed, broken  only  by  the  volcanic  activity  of  the  Coldbrook  group. 
The  Bloomsbury  rocks,  associated  with  rocks  unquestionably  of  Upper 
Devonian  age,  are  referred  to  the  same  horizon.  At  one  place  the 
Coldbrook  group  overlies  the  St.  John,  its  position  being  due  to  a  re- 
verse folding  caused  by  a  ridge  of  eruptive  syenite.  The  Kingston 
group  is  provisionally  referred,  on  its  general  lithological  character 
and  stratigraphical  relations,  to  the  Upper  Silurian,  although  Lower 
Silurian  and  Lower  Devonian  beds  may  occur. 
Matthew,8  in  1865,  correlates  the  Portland  series,  which  includes 
limestone,  syenite,  gneiss,  conglomerate,  slate,  and  graphitic  shale, 
with  the  Laurentian,  first,  because  of  its  lithological  characteristics, 
and  second,  because  it  is  unconformably  overlain  by  great  thicknesses 
of  deposits  similar  to  the  Huronian  scries  of  Canada.  The  Coldbrook 
Huronian  group  is  conformable  with  the  Lower  Silurian  St.  John 
beds,  although  there  is  a  marked  contrast  between  the  formations,  the 
former  containing  conglomerates  and  volcanic  products,  but  the  Latter 
none. 
