238  PRE-CAMBRIAN    ROCKS   OF    NORTH    AMERICA.  (bull.  86. 
the  other  hand,  it  is  also  a  possibility  that  there  is  a  physical  break 
between  the  elastics  and  crystallines  of  the  Laurentian,  but  no  frag- 
ments of  the  underlying  series  are  found  in  the  elastics  nor  is  any  struc- 
tural unconformity  mentioned.  One  is  at  once  struck  with  the  parallel- 
ism between  the  two  parts  of  the  Laurentian  of  southern  New  Brunswick 
and  those  of  the  Hastings  series.  In  this  latter  case  Vennor,  in  his  later 
work,  came  to  the  conclusion  that  the  clastic  series  is  a  newer  uncon- 
formable one  resting  upon  an  older  crystalline  series. 
The  Laurentian  and  Huronian  are  in  general  said  to  be  in  conformity. 
While  this  is  true,  Matthew  in  1865  states  that  the  Portland  series  is 
nnconformably  overlain  by  the  Huronian,  and  Ells  repeats  this  state- 
ment in  1879.  In  1880,  however,  this  position  is  apparently  abandoned ; 
at  least  it  is  not  alluded  to  in  the  general  summary  of  conclusions.  As 
the  Huronian  and  Laurentian  are  regarded  as  conformable,  the  basis 
for  separating  the  clastic  series  at  the  base  of  the  Ooldbrooks  must  be 
considered  wholly  lithological.  It  is  somewhat  difficult  to  determine 
the  lithological  criteria  used  in  the  distinction,  but  it  seems  that  the 
appearance  of  abundant  volcanic  material  is  the  most  important  of 
these.  Also  connected  with  this  fact  is  a  prevailingly  darker  color. 
When  it  is  remembered  that  volcanic  outbreaks  are  often  of  a  local 
character,  and  that  it  is  wholly  possible  that  quartzites  and  slates  are; 
being  deposited  at  the  same  time  volcanic  accumulations  are  occurring, 
it  must  be  concluded  that  the  criterion  of  volcanic  activity  is  an  uncer- 
tain one.  It  would  seem  that  it  would  be  more  reasonable,  without 
reference  to  other  localities,  to  make  the  major  break  above  the  crys- 
tallines of  the  Lower  Laurentian. 
The  only  physical  break  finally  maintained  in  the  whole  pre-Cam- 
brian  series  is  between  the  two  divisions  of  the  Huronian,  the  Cold- 
brook  and  Coastal.  From  the  descriptions  it  seems  that  this  break 
is  a  very  considerable  one;  for  detritus  of  the  lower  series  is  contained 
in  the  upper,  and  more  important  than  this,  the  lower  series  has  a 
steeper  inclination.  Such  a  break  as  this  certainly  implies  not  only  an 
erosion  interval,  but  an  orographic  movement,  and  this  must  mean  a 
rather  important  time  break. 
Throwing  aside  all  correlations  with  other  regions  and  considering, 
the  pre-Cambrian  succession  in  southern  New  Brunswick  alone,  it  is  as 
follows:  (1)  Wholly  crystalline  granites,  gneisses,  etc.     (2)  Quartzites, 
slates,  slate  conglomerates,  gneisses,  and  crystalline  limestones.     (3) 
Volcanics  and  elastics  of  the  Coldbrook.     Unconformity.     (4)  Coastal 
and  Kingston  groups.    While  in  the  reports  it  is  positively  stated  that 
the  Coldbrook  is  lower  than  the  Coastal  and  Kingston,  even  this  con- 
clusion apparently  can  not  be  taken  without  question,  since  the  dis 
tinction  is  abandoned  in  the  mapping.    The  dropping  of  the  terir 
Huronian  for  the  post-Laurentian  groups  indicates  that  this  correlatioi' 
with  Huronian,  taken  for  granted  for  many  years,  is  also  considered  ai 
open  question. 
