vanhise.]  DISCUSSIONS    OF    PRINCIPLES.  451 
series  of  crystalline  schists  and  gneisses.  But  the  moment  horizontal 
or  tangential  pressure  either  overcame  or  disturbed  the  action  of  the 
downward  pressure,  the  horizontal  arrangement  of  these  crystallizing 
materials  would  be  broken  up,  and  their  resulting  arrangement  would 
depend  upon  the  interaction  of  the  two  forces. 
Selwyn,11  in  1879,  proposes  the  following  general  stratigraphy  for 
the  older  rocks :  I.  Laurentian :  To  be  confined  to  all  those  clearly  lower 
unconformable  granitoid  or  syenitic  gneisses  in  which  we  never  find 
inter  stratified  bands  of  calcareous,  argillaceous,  arenaceous,  and  con- 
glomeratic rocks.  II.  Huronian :  To  include  (1)  the  typical  or  original 
Huronian  of  lake  Superior  and  the  conformably — or  unconformably,  as 
the  case  may  be — overlying  upper  copper-bearing  rocks;  (2)  the  Hast- 
ings, Templeton,  Buckingham,  Grenville,  and  Bawdon  crystalline  lime- 
stone series;  (3)  the  supposed  Upper  Laurentian  or  Norian;  (4)  the 
altered  Quebec  group  and  certain  areas  not  yet  defined  between  lake 
Matapedia  and  cape  Maquereau,  in  Gaspe ;  (5)  the  cape  Breton,  Nova 
Scotia,  and  New  Brunswick  pre-Primordial  subcrystalline  and  gneis- 
soid  groups.  III.  Cambrian:  In  many  of  the  areas,  especially  the 
western  ones,  the  base  of  this  is  well  defined  by  unconformity,  but  in 
the  Eastern  Townships  and  in  some  parts  of  Nova  Scotia  it  has  yet  to  be 
determined.  The  limit  between  it  and  Lower  Silurian  is  debatable 
ground.  One  point  is  particularly  insisted  on,  that  great  local  uncon- 
formities and  lithological  differences  may  exist  without  indicating  any 
important  difference  in  age,  especially  in  regions  of  mixed  volcanic  and 
sedimentary  strata,  and  that  the  fact  of  crystalline  rocks  (greenstones, 
diorites,  dolerites,  felsites,  norites,  etc.)  appearing  as  stratified  masses 
and  passing  into  schistose  rocks  is  no  proof  of  their  not  bein1  g  of  erup- 
tive or  volcanic  origin;  their  present  metamorphic  or  altered  character  is, 
as  the  name  implies,  a  secondary  phase  of  their  existence,  and  is  un- 
connected with  their  origin  or  original  formation  at  the  surface,  but  is 
due  partly  to  original  differences  of  composition  and  partly  to  the  va- 
rying physical  accidents  to  which  they  have  since  their  formations 
respectively  been  subjected, 
Selwyn,12  in  1881,  states  that  the  anorthosite  rocks  are  in  general 
conformity  with  the  crystalline  limestones,  but  are  occasionally  inter- 
fered with  and  disturbed  by  intrusions  ( ?)  of  the  more  massive  and 
granitoid  variety  of  labradorite.  This  is  proof  that  the  labradorite  or 
Norian  rocks  of  Hunt  do  not  constitute  an  unconformable  Upper  Lau- 
rentian formation,  but  occur  in  part  as  unstratified  intrusive  masses, 
and  in  part  as  interstratifications  with  the  orthoclase-gneisses,  quartz- 
ites,  and  limestones  of  the  Laurentian  system,  as  developed  in  the 
Grenville  region,  and  mapped  by  Logan. 
As  to  the  granites  which  have  been  regarded  as  intrusive  by  Logan, 
both  in  the  crystalline  and  fossiliferous  rock,  there  is  no  doubt  they 
are^of  later  origin  than  the  Silurian  rocks  which  surround  them,  and 
which  are  everywhere,  on  approaching  the  granite,  considerably  al- 
