226  PRE-CAMBRIAN   ROCKS    OF    NORTH    AMERICA.  [bull.*6. 
are  really  only  different  portions  of  one  and  the  same  mass.  It  is  con- 
cluded that  most,  if  not  all,  of  the  areas  are  of  eruptive  origin,  since 
they  are  frequently  found  cutting  the  gneisses.  Bands  of  crystalline 
limestone  are  found  in  the  region. 
Ells,10  in  1890,  states  that  the  lowest  beds  of  the  Lower  Cambrian 
frequently  contain  a  very  considerable  thickness  of  conglomerates,  the 
pebbles  of  which  are  without  doubt  derived  from  the  underlying  crys- 
talline ridges  which  have  been  called  pre-Cambrian.  They  are  distinct 
in  character  from  the  pre-Cambrian  of  the  anticlinals,  the  latter  being 
in  all  cases  highly  crystalline,  while  there  is  a  sharply  defined  line, 
either  of  unconformable  overlap  or  of  fault,  between  the  crystalline 
series  and  the  slates  and  quartzites  of  what  has  been  styled  Lower 
Cambrian.  This  line  of  fault  is  to  be  seen  at  certain  points,  and  is 
heavy ;  at  others  the  slates  occupy  basin -like  areas  infolded  in  the 
schists,  where  the  rocks  pass  at  once  from  the  black,  gray,  and  purple 
slates  to  the  highly  altered  schists.  There  are  certain  areas  of  mica- 
schists  and  black  slates  which  are  apparently  in  the  center  of  the 
anticlinal  of  Sutton  or  the  Chaudiere.  These  probably  represent  a 
portion  of  the  pre-Cambrian,  but  they  are  quite  distinct  from  the  or- 
dinary black,  purple,  and  gray  slates  and  quartzites  of  the  Chaudiere 
gold  series. 
SUMMARY   OF   RESULTS. 
A  large  number  of  articles  have  been  written  in  reference  to  the 
Quebec  group  which  are  not  touched  in  the  above,  as  their  point  of 
view  is  paleontological,  and  if  the  crystallines  are  referred  to  at  all  they 
are  simply  placed  as  the  metamorphosed  equivalents  of  the  fossiliferous 
rocks. 
While  Ells  places  the  middle  series  found  in  this  region  as  Cambrian, 
he  is  very  cautious  to  say  that  he  has  no  paleontological  evidence  for 
this ;  so  that  it  is  yet  to  be  considered  an  open  question  whether  it  is 
Algonkian  or  not.  By  Selwyn  it  is  compared  with  the  Keweenawan, 
and  by  Ells  with  the  Nova  Scotia  gold-bearing  slates.  It  is  certain  that 
the  series  is  uncomformably  below  the  Potsdam,  and  equally  certain  that 
it  overlies  crystalline  schists.  While  the  so-called  Cambrian  and  pre- 
Cambrian  are  said  to  be  unconformable,  and  several  localities  are  cited  in 
which  these  relations  obtain,  one  wishes  that  they  had  been  described  in 
more  detail.  The  only  one  mentioned  in  which  the  facts  are  given  upon 
which  the  statement  of  uncomformity  is  based  is  the  one  on  the  Quebec 
railway,  where  it  is  said  that  the  strike  of  the  Cambrian  slates  is  almost 
at  right  angles  to  that  of  the  pre-Cambrian  schists.  When  it  is  remem- 
bered that  there  probably  are  in  this  region  great  masses  of  intrusive 
granites  which  have  metamorphosed  the  adjacent  strata,  and  that  as  a 
result  of  such  action  a  schistose  structure  oftentimes  develops  inde- 
pendent of  the  original  bedding,  the  evidence  cited  at  this  particular 
locality  is  by  no  means  sufficient  to  establish  the  conclusion.     However, 
