OUTLINE  OF  THIS  P  A  P  E  R . 
This  book  is  a  review  of  the  present  state  of  knowledge  of  the  general  structure  of 
the  pre-Cambrian  rocks  of  the  United  States  and  Canada,  The  material  contained 
in  the  historical  chapters  is  of  two  kinds :  Summaries  of  all  articles  pertaining  to  the 
subject  considered,  and  summaries  of  the  conclusions  which  appear  to  be  established. 
The  first  represents  the  substance  of  the  literature ;  the  second  brings  together  the 
important  ascertained  structural  facts,  and  oftentimes  becomes  a  more  or  less  extended 
discussion.  The  final  chapter  covers  the  same  grounds  as  the  historical  chapters  for 
the  various  pre-Cambrian  general  successions  proposed  by  different  authors,  and  also 
contains  a  discussion  of  results  and  the  principles  upon  which  they  are  based.  Within 
the  chapters,  individual  districts  or  regions  are  given  separate  sections,  and  the  sum- 
mary of  literature  for  each  is  arranged  in  chronological  order.  As  used  in  this  vol- 
ume, the  term  Cambrian  is  defined  as  delimited  below  by  the  base,of  the  Olenellus 
fauna;  Algonkian  includes  the  pre-Olenellus  elastics  and  their  equivalent  cry  si  ;il- 
lines;  while  the  Archean  includes  the  completely  crystalline  rocks  below  the  Al- 
gonkian. 
The  several  chapters  have  the  following  scopes:  Chapter  I:  The  Original  Lauren- 
tian  and  Huronian  areas — treats  of  eastern  Ontario  and  western  Quebec,  and  the  area 
from  the  north  channel  of  lake  Huron  to  lake  Temiscamang.  Chapter  II:  Lake 
Superior  Region— summarizes  the  work  of  the  official  geologists  of  the  Canadian 
Survey  and  associates,  of  the  early  United  States  geologists  and  associates,  of  the 
Michigan  geologists  and  associates,  of  the  Wisconsin  geologists  and  associates,  of 
the  Minnesota  geologists  and  associates,  of  the  later  United  States  geologists  and 
associates,  and  gives  a  summary  and  discussion  of  results.  Chapter  III :  The  Great 
Northern  Area — treats  of  the  region  about  Hudson  bay,  northern  Canada,  and  the 
lower  St.  Lawrence  river  region.  Chapter  IV :  Eastern  Canada  and  Newfoundland — 
treats  of  the  Eastern  townships,  Gaspe  peninsula,  central  New  Brunswick,  southern 
New  Brunswick,  Nova  Scotia  and  cape  Breton,  and  Newfoundland.  Chapter  V: 
Isolated  Areas  of  Dakota,  Missouri  and  Texas — treats  of  the  Black  hills,  the  pre- 
Cambrian  of  Missouri,  and  the  central  Mineral  region  of  Texas.  Chapter  VI:  The 
Cordilleras — treats  of  the  many  mountain  ranges  in  the  far  west.  Chapter  VII : 
Eastern  United  States — treats  of  the  New  England,  Middle  Atlantic,  and  Southern 
Atlantic  states.  Chapter  VIII:  General  Successions  and  Discussions  of  Principles — 
summarizes  the  various  general  successions  proposed,  suggests  one,  and  discusses  the 
principles  of  pre-Cambrian  stratigraphy. 
The  more  important  conclusions  of  this  chapter  are  as  follows :  The  Archean  is  the 
basal  complex  of  America.  It  has  everywhere,  if  large  areas  are  considered,  an 
essential  likeness.  It  consists  mainly  of  granitic,  gneissic  and  schistic  rocks,  among 
which  are  never  found  beds  of  quartzite,  limestone,  or  any  other  indubitable  elastics. 
One  kind  of  rock  may  occupy  considerable  areas,  but  when  different  kinds  are  asso- 
ciated their  structural  relations  are  most  intricate.  These  relations,  as  well  as  the 
completely  crystalline  schistose  character  of  the  rocks,  the  frequent  broken  and  dis- 
torted forms  of  the  mineral  constituents,  and  their  involuted  foldings,  are  evidence 
that  these  most  ancient  rocks  have  passed  through  repeated  powerful  dynamic  move- 
ments. 
As  to  the  origin  of  the  Archean  rocks,  three  different  views  are  proposed  :  (1)  They 
may  be  considered  as  metamorphosed  detrital  rocks.  (2)  They  .may  be  considered  as 
igneous  and  later  in  origin  than  certain  of  the  pre-Cambriati  elastics.  (3)  They  may 
be  considered  as  igneous  and  representing  either  a  part  of  the  earth's  original  crust 
or  else  originally  crystallized  material  which  has  now  reached  the  surface  ;is  a  conse- 
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