an  hisb.]  EASTERN    UNITED    STATES.  365 
;hesyen  te  into  the  greenstone  porpbyry.  The  obscurely  stratified  rocks 
>u  the  border  of  the  great  syenite  mass  at  Quincy  prove  the  igneous 
nfluence  of  the  eruptive  syenite  upon  the  upturned  strata  which  it  had 
elevated  by  its  protrusion. 
Dana,45  in  1872,  maintains  from  the  descriptions  of  full  sections  that 
it  Great  Barrington  is  a  conformable  succession  of  quartzites,  lime- 
stones, mica- schists  and  gneisses.  The  layers  of  quartzite  are  found 
ilong  the  strike  to  change  to  mica-schist  and  gneiss.  This  series,  many 
if  them  later  in  age  than  the  Stockbridge  limestone,  is  similar  to  the 
Irreen  mountain  series,  which  has  been  regarded  on  lithological  evidence 
:o  be  pre- Silurian.  The  Stockbridge  limestone,  on  fossiliferous  evidence, 
s  found  to  be  either  Silurian  or  younger.  It  appears  that  lithological 
evidence  is  a  very  uncertain  test  as  to  geological  age,  as  crystalline 
•ocks  are  found  later  than  the  Stockbridge  limestone;  as  quartzite 
•hanges  into  mica-slate,  schist  or  gneiss,  these  into  hydromica-slates, 
tnd  these  into  chloritic  mica-slate. 
Hunt/6  in  1872,  states  that  the  rocks  seen  in  the  vicinity  of  Boston 
consist  of  three  classes,  crystalline  stratified  rocks,  eruptive  granites, 
tnd  unaltered  slates,  sandstones,  and  conglomerates.  The  crystalline 
Gratified  rocks  include  the  felsite-porphyries,  nonporphyritic  and  jas- 
ler-like  varieties,  and  porphyri tic  syenite ;  while  the  second  division  in- 
■  hides  dioritic  and  chloritic  rocks,  sometimes  schistose,  and  frequently 
imygdaloidal.  These  rocks  are  penetrated  by  intrusive  granites,  gen- 
erally more  or  less  hornblendic,  the  syenites  of  Hitchcock,  and  others. 
\f  several  places  the  phenomena  of  disruption  and  inclosure  of  broken 
ragments  of  rock  in  the  granite  are  well  seen,  the  lines  of  contact  be- 
ng  always  sharp  and  well  defined.  The  third  class,  consisting  of  the 
in  altered  argil  lites  of  Brain  tree,  containing  the  Primordial  fauna,  were 
bnnd  to  rest  directly  upon  the  hard  porphyritic  felsite  of  the  ancient 
ieries,  the  line  of  demarcation  being  very  distinct.  At  other  places 
eddish  granulites  directly  underlie  the  black  argillites,  and  in  several 
)laces  quartzites  with  conglomerates  are  observed  in  contact  with  the 
>ld  dioritic  and  epidotic  rocks.  The  Koxbury  conglomerate  contains 
)d)b]es  of  the  felsite-porphyries,  diorites,  and  intrusive  granites  of  the 
pier  series,  besides  fragments  of  argillaceous  slate. 
Burbank,47  in  1872,  states  that  the  bands  of  crystalline  limestone 
hat  occur  in  the  granitic  gneiss  which  extends  in  a  southwesterly  di- 
•eetion  from  near  the  mouth  of  the  Merrimac  river,  supposed  to  contain 
Sozoon,  are  not  true  stratified  rocks,  but  are  subsequent  deposits  of  a 
fein-like  character.  As  evidence  of  this  are  cited  the  facts  that  the 
principal  deposits  occur  along  the  line  of  an  anticline,  filling  cavities 
produced  by  the  folding  and  falling  down  of  portions  of  the  included 
strata  of  the  gneiss.  The  deposits  are  all  of  very  limited  extent,  the 
largest  appearing  at  the  surface  not  more  than  220  feet  in  length,  the 
ridest  pari  being  about  00  feet.  The  aggregate  length  of  all  the  lime- 
stone deposits  occurring  in  a  line  some  25  miles  in  length  is  probably 
