van  hise.1  EASTERN    UNITED    STATES.  385 
are  completely  metamorphosed  material.  He,  however,  includes  among 
the  metamorphic  rocks  diorite,  quartz-diorite,  and  amphibolite,  since 
they  have  marked  distinctions  from  the  fresh  basic  rocks  recognized  as 
eruptives.  From  the  assumption  that  cleavage  foliation  and  stratifica- 
tion generally  correspond  have  probably  resulted  more  mistakes  than 
from  any  other  cause. 
The  cautious  work  of  Adams,  the  elder  Hitchcock  and  Percival  in 
correlation  is  noticeable.  Adams  preferred  to  call  the  rocks  of  Ver- 
mont Azoic,  referring  to  their  present  state,  aud  specifically  saying  that 
many  of  them  might  prove  quite  late  in  the  fossiliferous  series.  The 
same  course  is  followed  by  the  elder  Hitchcock,  who  says  that  probably 
most  of  the  Yermout  rocks  will  prove  to  be  later  than  the  Laurentian 
of  Logan.  Percival,  in  Connecticut,  carefully  described  the  rocks  as 
they  occurred  without  attempting  to  give  any  succession  or  to  correlate 
them  with  other  rocks.  The  building  up  of  successions  upon  insufficient 
data  and  crude  correlations  is  mainly  the  work  of  later  men. 
The  work  of  Dana,  Pumpelly,  Emerson,  Dale,  Wolff,  and  Walcott  in 
the  past  decade  marks  a  new  epoch  in  the  study  of  the  crystalline  rocks 
of  New  England.  The  complexity  of  the  problem  has  been  for  the  first 
time  appreciated.  It  has  been  seen  that  the  old  method  of  making  a 
few  sections  wide  apart  across  a  district,  and  bringing  the  discrepan- 
cies into  harmony  by  assumptions,  wherever  necessary,  of  inversions 
and  faults,  and  making  correlations  of  formations  with  those  of  distant 
regions  because  of  lithological  likenesses,  can  lead  only  to  conclusions 
worse  than  valueless. 
In  applying  the  new  method  of  work,  as  exemplified  in  western 
Massachusetts,  it  has  not  been  assumed  that  a  rock  stratum  is  the 
equivalent  of  another  stratum  in  a  different  locality.  In  order  to  es- 
tablish equivalence  it  is  necessary  that  the  two  be  actually  traced  to- 
gether, or  else  that  unquestionable  fossil  evidence  be  found.  Instead 
of  assuming  that  stratification  and  cleavage  foliation  correspond,  the 
assumption  has  been  rather  that  they  usually  do  not  correspond  and 
that  nothing  can  be  taken  as  bedding  which  can  not  be  demonstrated 
to  be  this,  as,  for  instance,  the  contact  planes  of  two  formations,  such 
as  quartzite  and  limestone  or  one  of  these  with  schist.  Instead  of  build- 
ing up  a  structure  from  a  few  sections  wide  apart,  all  sources  of  informa- 
tion have  been  sought;  every  outcrop  was  visited;  the  information 
furnished  by  artificial  excavations  was  utilized;  full  suites  of  specimens 
were  collected,  and  all  the  light  which  can  be  furnished  by  the  modern 
petrographical  methods  has  been  brought  to  bear  upon  the  problems. 
Finally,  a  more  careful  search  for  fossils  has  revealed  their  presence  in 
rocks  so  crystalline  that  former  search  has  resulted  in  failure.  In  this 
study  Pumpelly,  besides  using  these  and  other  well  known  principles, 
has  formulated  new  ones.     These  are : 
(1)  The  degree  and  direction  of  the  pitch  of  a  fold  are  indicated  hy  those  of  the 
axes  of  the  minor  plications  on  its  sides.  (2)  When  the  strike  of  the  stratification 
foliation  and  cleavage  foliation  differ  in  the  same  rock,  this  is  regarded  as  indi- 
Bull.  86 25 
