A  REVIEW  OF  THE  PRESENT  STATE  OF  KNOWLEDGE 
OF  THE  PRE-CAMBRIAN  ROCKS  OF  NORTH  AMERICA. 
By  0.  R.  Van  Hise. 
INTRODUCTION. 
The  purpose  of  this  book  is  to  give  an  account  of  the  present  state  of 
knowledge  of  the  general  structure  of  the  pre-Cambrian  of  the  United 
States  and  Canada.  It  is  not  a  bibliography  of  pre-Cambrian  litera- 
ture, nor  a  petrography  of  the  pre-Cambrian  rocks,  nor  a  treatment  of 
metamorphism,  nor  an  account  of  economic  facts.  Mere  occurrences  of 
pre-Cambrian  or  crystalline  rocks  are  not  referred  to  unless  the  districts 
are  new.  Petrography,  metamorphism,  and  economic  geology  are  con- 
sidered only  so  far  as  they  have  a  direct  bearing  upon  structural  re- 
sults, and  then  the  substance  of  the  established  conclusions  is  given 
rather  than  the  facts  upon  which  they  are  based  and  the  manner  of 
reaching  them. 
The  material  contained  in  the  historical  chapters  of  this  volume  is  of 
two  kinds:  First,  a  summary  of  all  articles  or  parts  of  articles  which 
have  contributed  knowledge  upon  the  subject  considered;  and  second, 
summaries  of  the  conclusions  which  appear  to  be  established  in  the 
various  regions,  while  the  final  chapter  covers  the  same  ground  for 
general  successions  proposed  and  also  a  discussion  of  these  results  and 
the  principles  upon  which  they  are  based.  IsTo  summaries  are  made  of 
writings  based  wholly  upon  the  field  work  and  reports  of  others.  This 
report  is  not  a  review  of  reviews  j  neither  is  purely  controversial  liter- 
ature noticed.  When  a  paper  is  made  up  in  part  of  an  original  investi- 
gation and  of  a  discussion  of  the  works  of  others,  only  the  first  part  is 
summarized.  When  the  same  writer  repeats  the  same  facts  and  con- 
clusions several  times,  summary  is  made  of  the  most  comprehensive 
article  and  references  are  made  to  the  others  in  the  footnotes.1  Often- 
times a  final  report  includes  all  found  in  several  annual  reports.  In 
this  case  the  final  report  only  is  summarized.  In  making  summaries 
the  conclusions  reached  by  the  various  authors  are  always  given,  and 
as  full  an  account  of  the  facts  upon  which  they  are  based  as  is  possible 
without  extending  this  book  beyond  bounds. 
1  At  the  end  of  each  chapter. 
