SUMMARY   OF   GENERAL   LITERATURE. 
In  the  crystalline  schists  and  gneisses  are  found  identically  the  same 
minerals  which  characterize  the  granites.  In  the  schists  the  charac- 
teristic feature  is  the  parallel  bedded  arrangement.  Granite  possesses 
the  same  minerals;  the  sole  difference  seems  to  be  that  granite  is  often 
demonstrably  a  plastic  intrusion  and  possesses  no  parallel  arrangement 
of  minerals.  The  geognostic  position  of  the  schists  is  exactly  like  that 
of  the  other  strata  which  were  deposited  horizontally  and  afterward 
disturbed.  On  the  other  hand,  granite  in  an  immense  majority  of 
cases  is  found  exposed  in  the  hearts  of  the  mountain  ranges.  It  is  only 
when  we  can  observe  granite  in  direct  connection  with  the  strata  into 
which  it  has  intruded  or  out  of  which  it  has  been  made  that  the  true 
relations  can  be  seen;  and  it  is  safe  to  say  that  wherever  these  inti- 
mate relations  are  observable  the  granite  occupies  a  region  which  has 
been  subjected  to  horizontal  or  circumferential  pressure.  The  frequent 
phenomena  of  the  underdip  of  the  strata  flanking  a  granite  mass,  as 
in  the  great  granite  body  of  the  Sierra  Nevada,  are  prominent  in- 
stances of  the  intimate  relation  spoken  of.  If  in  such  eases  an  uncon- 
formable overlying  and  unaltered  series  were  to  cover  all  but  the 
summits  of  the  granite  hills,  the  granite  would  appear  simply  as  an 
unconformable  underlying  body  whose  genetic  relations  are  absolutely 
unknown.  In  this  category  a  vast  number  of  granite  exposures  of  the 
Cordilleras  have  to  be  placed. 
It  is  an  invariable  law,  then,  that  where  the  genetic  relations  are 
clearly  perceived  eruptive  granite  is  always  found  in  connection  with 
very  great  horizontal  pressure  and  consequent  disturbance.  Suppose, 
now,  a  deep-lying  series  of  varied  sedimentary  beds,  covered  by  a  suffi- 
cient superimposed  mass  to  exert  a  pressure  powerful  enough  to  sink 
them  to  the  necessary  thermal  horizon  for  the  induction  of  crystalliza- 
tion in  the  material  of  the  beds.  As  long  as  the  attitude  of  these  beds 
was  undisturbed  by  horizontal  compression  the  result  Would  be  a 
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  syenitie  gneisses  in  which  we  never 
find  interstratified  bands  of  calcareous,  argillaceous,  arenaceous,  and 
conglomeratic  rocks.  II.  ITuronian  :  To  include  (1)  the  typical  or 
original  Huronian  of  Lake  Superior  and  the  conformably  -or  uncon- 
formable, as  the  case  may  be — overlying  upper  copper-bearing  rocks; 
(2)  the  Hastings.  Templeton,  Buckingham,  Grenville,  and  Rawdon 
crystalline  limestone  series;  (3)  the  supposed  [Jpper  Laurentian  or 
Norian;   (4)  the  altered  Quebec  group  and  certain  areas  not  ye4  de- 
