488  PEB-CAMBRIAN    GEOLOGY    OF    NOETH   AMEEICA. 
the  Sutton  Mountain  range,  and  are  placed  on  the  map  as  doubtfully 
Huronian. 
Cutting  the  pre-Cambrian  rocks,  and  possibly  also  later  sediments, 
are  rocks  having  a  considerable  variety,  such  as  granites,  syenites,  dio- 
rites,  diabases,  serpentines,  traps,  etc.,  evidently  of  different  ages.  It 
is  probable  that  the  age  of  the  granites  is  not  far  from  the  close  of  the 
Silurian  period. 
Dresser,  1X  in  1902,  concludes:  (1)  That  at  least  the  greater  part  of 
the  pre-Cambrian  or  crystalline  belts  of  the  Eastern  Townships  of 
Quebec  is  of  igneous,  not  sedimentary,  origin,  as  has  been  hitherto 
supposed.  (2)  That  these  rocks  are  allied  to  the  volcanics  of  South 
Mountain,  Pennsylvania,  especially  to  the  basic  types,  and  indicate 
the  continuance  of  this  class  of  rocks  throughout  the  Appalachians, 
as  was  suggested  by  Williams.  (3)  That  the  sediments  of  the  region, 
which  possibly  all  belong  to  the  Quebec  group,  were  deposited  be- 
tween and  upon  the  preexisting  ridges  of  igneous  material,  which  are 
now  being  uncovered  by  denudation,  while  the  intervening  valleys 
still  remain  deeply  filled. 
SUMMARY  OF  PRESENT  KNOWLEDGE. 
The  following  summary  has  been  prepared  by  John  A.  Dresser : 
The  jDre-Cambrian  of  the  Eastern  Townships  of  Quebec  south  of 
St.  Lawrence  River  comprises  three  principal  areas,  which  form  nar- 
row belts  conforming  to  the  Appalachian  folds.  They  are  designated 
the  Sutton  Mountains,  the  Stoke  Mountain,  and  the  Lake  Megantic 
areas,  the  first  and  second  being  extensions  of  the  Green  Mountains 
of  Vermont,  the  third,  a  continuance  of  the  White  Mountains  of  New 
Hampshire.  These  belts  consist  principally  of  ridges  of  volcanic  rock 
of  the  quartz  porphyry  andesite  series,  which  are  the  oldest  rocks  of 
the  region.  They  are  highly  altered  and  have  long  been  mistaken  for 
sediments,  and  have  been  correlated  accordingly.  They  represent  the 
chloritic,  epidotic,  nacreous,  and  much  of  the  micaceous  schists,  as 
well  as  considerable  portions  of  the  argillites  of  the  earliest  reports. 
In  position  they  apparently  belong  to  the  more  westerly  of  the  vol- 
canic belts  pointed  out  by  the  late  G.  H.  Williams  as  running  through- 
out the  Appalachians.  On  the  ground  of  their  similarity  to  the  other 
rocks  of  this  belt  they  are  thought  to  be  of  pre-Cambrian  age. 
Associated  with  these  volcanics  are  dolomites,  quartzites,  gray- 
wacke,  and  mica  schists,  which  in  many  places  appear  to  be  older  than 
the  Paleozoic  strata  of  the  basins  intervening  between  the  ridges  of 
volcanics.  In  other  places  they  can  not  be  separated  from  those  rocks. 
On  the  whole,  it  can  at  present  only  be  said  that,  while  it  is  possible 
and  even  probable  that  there  are  pre-Cambrian  sediments  in  this  re- 
gion, it  can  not  yet  be  regarded  as  proved  that  such  is  the  case. 
