356  I'KK-CAMBRIAN    ROCKS    OF    NORTH    AMERICA*.  [bull. 86. 
recent;  as  the  Ohainplain  rocks.  In  the  Green  mountains  are  quartz- 
rock,  gneiss,  talciferous  limestone,  quartz-gneiss  and  limestone  which 
are  supp3sed  to  be  Taconic.  Dikes  of  greenstone  cut  through  all  the 
divisions  of  the  stratified  rocks  and  are  therefore  more  recent  than  any 
of  them. 
Adams,19  in  1847,  gives  additional  details  as  to  the  rock  occurrences 
in  particular  localities. 
Thompson,20  in  1856,  states  that  the  Green  mountains  form  the  center 
of  an  anticlinal  axis,  the  dips  increasing  both  east  and  west  from  the 
principal  summits.  Slates,  schists  and  quartzites  are  found  which 
contain  a  few  obscure  fossils,  and  are  referred  to  the  Taconic  system. 
Hitchcock  (Edward),21  in  1861,  divides  the  rocks  in  general  into 
Stratified  or  Aqueous  and  TJnstratified  or  Igneous.  With  the  latter 
are  placed  granitic,  trappean  and  volcanic  rocks.  The  former  are  sub- 
divided into  Fossiliferous  and  Unfossiliferous,  or  Azoic.  In  this  latter 
division  are  placed  clay-slate,  quartz-rock,  mica-schist,  talcose. schist, 
and  chlorite- schist,  steatite  or  soapstone,  serpentine,  hornblende-schist, 
gneiss,  and  crystalline  limestone.  The  important  practical  question 
with  respect  to  the  metamorphic  rocks  is,  what  was  the  original  rock 
from  which  the  metamorphosed  deposit  was  derived?  In  not  a  few 
instances  so  complete  has  been  the  metamorphism  that  it  can  not  be 
told  whether  the  rock  belongs  to  the  oldest  of  the  crystalline  rocks  or 
is  earlier  than  the  Silurian  or  Cambrian.  While  the  degree  of  meta- 
morphism gives  no  clue  as  to  the  age  of  the  rocks,  from  other  evidence  it 
is  probable  that  most  of  the  highly  metamorphosed  rocks  of  Vermont 
are  altered  Devonian  and  Silurian.  In  the  western  part  of  the  state, 
aud  especially  that  part  of  New  York  that  lies  southwesterly,  are  found 
these  fossiliferous  rocks  but  little  altered,  and  these  form  a  starting 
point  for  the  Green  mountain  rocks  and  those  farther  east. 
Metamorphism  is  made  to  apply  to  any  transformation  of  any  kind 
of  rock  into  another.  At  Newport,  Ehode  Island,  East  Wallingford 
and  Plymouth,  Vermont,  are  found  schist-conglomerates  in  which  the 
pebbles  are  elongated  very  much  in  the  direction  of  their  strike.  They 
are  flattened,  but  not  so  strikingly  as  elongated  ;  they  are  indented  deeply 
into  each  other;  they  are  sometimes  a  good  deal  bent;  they  are  cut 
across  by  parallel  joints  and  fissures.  At  times  the  process  has  gone 
so  far  as  to  merge  the  pebbles  together,  and  as  to  scarcely  present  the 
appearance  of  ordinary  pebbles.  If  the  talcose  conglomerate  schist  is 
looked  at  on  the  edge  corresponding  to  the  dip,  nothing  is  seen  but 
alternate  folia  of  quartz  and  talc  and  mica,  and  the  rock  would  be  pro* 
nounced  a  good  example  of  a  talcose-schist.  But  a  fracture  at  right 
angles  reveals  the  flattened  pebbles,  and  shows  that  their  edges  are 
what  have  been  regarded  as  folia.  If  the  process  of  flattening  was 
carried  a  little  farther  no  evidence  would  remain  that  they  were  ever 
pebbles.  How  extensively  the  process  has  been  carried  through,  thus 
producing  schists  and  gneisses  from  conglomerates  in  the  Green  nioun- 
