van  hise.]  EASTERN    UNITED    STATES.  375 
most  reliable  structural  data  on  Greylock  have  been  obtained  from 
outcrops  where  two  different  beds  were  in  visible  contact,  or  from  a 
series  of  related  outcrops  in  all  of  which  both  cleavage  filiation  and 
stratification  foliation  were  equally  manifest  and  discordant,  or  else 
from  large  surfaces  of  rock  at  right  angles  to  the  strike  where  the 
general  trend  of  the  minor  folds  could  be  distinctly  seen.  As  a  re- 
sult of  a  large  number  of  observations  the  difference  in  angle  of  dip 
between  the  cleavage  foliation  and  stratification  foliation  was  found  to 
be  from  10°  to  120°.  When  the  difference  is  over  90°  the  direction  of 
the  two  dips  is  opposite.  The  absolute  dip  of  cleavage  in  a  large 
number  of  cases  is  almost  universally  to  the  east.  Also,  there  is  lack 
of  conformity  in  the  strikes  of  the  cleavage  foliation  and  stratification 
foliation. 
Early  in  the  work  attention  was  directed  by  Pumpelly  to  methods  of 
detecting  the  pitch  in  the  axes  of  folds.  It  is  usually  determined  by 
observing  the  pitch  of  the  axis  of  any  part  of  the  fold.  The  correct- 
ness of  the  method  seems  to  be  verified  by  the  general  parallelism 
which  exists  between  the  minute  and  general  structure  of  the  rock 
masses,  and  also  by  the  opposite  direction  of  the  pitch  as  determined 
at  the  extreme  ends  of  the  mountains.  An  application  of  these  prin- 
ciples to  Greylock  shows  that  the  range  consists  of  a  series  of  more 
or  less  open  or  compressed  synclines  and  anticlines  which,  beginning 
near  North  Adams,  increase  southerly  in  number  and  altitude  with  the 
increasing  width  and  altitude  of  the  schist  area,  and  then,  from  a  point 
about  a  mile  and  a  half  south  of  the  summit,  begin  to  widen  out,  and 
to  diminish  in  number  and  height  until  they  finally  pass  into  a  few 
broad  and  low  undulations  west  of  Cheshire.  Between  that  point  and 
the  villages  of  Berkshire  and  Lanesboro  the  folds  become  sharper  ami 
more  compressed  and  the  schist  area  rapidly  narrows,  terminating 
within  a  short  distance  of  Pittsfield. 
Mount  Greylock,  with  its  subordinate  ridges,  is  then  a  synclinorium, 
consisting  at  the  surface  of  eleven  synclines  alternating  with  as  many 
anticlines,  but  in  carrying  the  sections  downward  they  are  resolved 
into  two  great  synclines  with  several  lateral  and  minor  ones.  There 
are  five  more  or  less  distinct  lithological  horizons  in  the  Greylock  mass. 
Beginning  above,  the  succession  and  correlations,  with  the  classifica 
tions  of  E.  Emmons,  James  Hall,  Dana  and  Walcott,  are  as  follows: 
