224  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86.   j 
Selwyn,5  in  1883,  in  further  speaking  of  the  Quebec  group,  asserts 
of  the  upper  metamorphic  or  volcanic  group  that  neither  a  schistose  nor 
a  bedded  structure  can  be  accepted  as  a  proof  of  nonigneous  origin,  and  ] 
that  a  massive  lava  flow  is  as  likely,  through  pressure  and  metamor-  ] 
phism,  to  assume  a  schistose  structure  as  are  ordinary  sedimentary 
strata.    Much  of  the  material  of  the  upper  part  of  the  lower  groups  is 
of  contemporaneous  irruptive  and  eruptive  origin,  though  for  the  most 
part,  through  cleavage  and  alteration,  so  changed  in  external  and] 
physical  character  as  to  cause  these  rocks  to  be  classed  as  metamor- 
phic, notwithstanding  that  they  still  closely  correspond  in  chemical \ 
composition  with  recognized  igneous  and  volcanic  rocks,  and  differ  es-  j 
sentially  from  any  known  ordinary  unmixed  sedimentary  deposits.    It  is  j 
suggested  that  the  upper  volcanic  group  may  represent  the  Keeweenian. 
Ells,6  in  1887,  reports  on  the  geology  of  a  portion  of  the  Eastern. 
Townships.  Placed  in  the  Cambrian  are  a  set  of  slates  of  various  colors, 
sandstones  passing  into  quartzites,  quartziferous  schists  and  conglom- 
erates in  which  are  found  no  calcareous  beds  or  fossils.  The  conglom- 
erates are  of  two  kinds ;  one  is  composed  of  pebbles  of  the  ordinary  kind, 
granitoid  rocks,  quartzites,  slates,  etc. ;  the  other  is  composed  largely 
of  dioritic  pebbles  in  a  diorite  paste  with  intercalated  beds  of  sandstones 
and  grits,  and  may  be  regarded  as  an  agglomerate.  This  series  in 
places  is  certainly  unconformable  to  the  Cambro- Silurian  system  on  the' 
one  hand,  and  in  a  like  manner  is  unconformable  to  the  underlying^ 
ridges  of  crystalline  rocks  from  the  debris  of  which  they  are  largely 
formed.  These  strata  for  the  most  part  flank  the  ridges  of  crystalline 
schists  and  gneisses,  but  at  other  times  are  in  intricately  folded  basins 
in  them.  These  rocks  resemble  the  gold-bearing  series  of  Nova  Scotia. 
When  near  to  or  cut  by  masses  of  granite  the  strata  have  developed  in 
them  crystals  of  chiastolite  and  staurolite. 
The  areas  of  crystalline  schists,  gneisses,  and  limestones,  with  Serpen- 
tines and  associated  strata  are  referred  to  the  pre- Cambrian.  The  age 
of  these  rocks  is  inferred  from  their  lithological  character,  from  their 
position  of  apparent  unconformity  below  the  overlying  series  referred 
to  the  Cambrian,  and  from  the  fact  that  their  debris  is  found  in  the 
latter  series.  The  areas  of  pre-Cambrian  rocks  are  four  in  number.  In 
position,  and  in  the  fact  that  they  contain  copper,  they  closely  resemble 
the  copper-bearing  rocks  of  New  Brunswick  and  the  Huronian  of  Bruce 
mines.  There  is  a  similarity  to  the  series  in  England  and  Scotland 
described  by  Hicks  under  the  names  of  Dimetian,  Arvonian,  and  Pebid- 
ian.  Summing  up  it  is  said :  Whatever  may  be  the  exact  age  of  these 
altered  rocks,  their  present  aspect  entitles  them  to  be  classed  as  very 
ancient  sediments,  although,  in  view  of  the  great  alterations  which 
may  result  from  intense  regional  metamorphism,  there  is  no  reason  why 
many  of  the  ordinary  sedimentary  rocks  of  Cambrian,  Cambro- Silurian, 
or  even  Silurian  age,  should  not  assume  much  of  the  character  of  these 
just  described.    It  is  now  tolerably  clear  that  the  series  now  considered 
