NEW    ENGLAND.  575 
In  the  Huronian  distinctly  bedded  rocks  are  the  exception.  Although 
many  apparently  structureless  rocks  are  probably  really  stratified,  it 
is  undoubtedly  true  that  a  large  part,  perhaps  the  greater  part,  of  the 
formation  has  been  more  or  less  fluid,  and  extravasation  may  be  set 
down  as  a  characteristic  structural  feature.  Besides  cutting  various 
rocks,  the  granite  at  many  points  contains  angular  fragments  of  the 
mica  slates  at  the  contact.  The  induration  of  the  slate  and  conglom- 
erate at  points  where  they  adjoin  the  granite,  with  the  frequent  devel- 
opment of  amygdaloid  characters,  are  facts  which  tell  strongly  in 
favor  of  the  igneous  character  of  the  granite.  The  petrosilex  is  fre- 
quently cut  by  the  granite,  but  the  reverse  is  never  the  case.  There 
is  an  apparent  transition  between  the  granite  and  the  petrosilex  or 
porphyry.  The  two  are  regarded  as  conformable,  both  having  been 
metamorphosed  from  the  same  set  of  sediments,  the  more  crystalline 
character  of  the  granite  being  due  to  its  greater  depth.  With  the 
diorite  are  included  all  the  basic  rocks  which  have  been  fluid.  These 
blend  with  and  grade  into  the  stratified  hornblende  gneisses. 
The  Montalban  series  in  the  area  covered  is  the  most  important  of 
the  three  systems.  It  comprises  the  ascending  conformable  succession, 
granite,  gneiss,  mica  slate,  argillite,  and  limestone,  although  subordi- 
nate breaks  of  no  great  importance  occur.  The  granite  acts  as  an 
exotic  to  a  large  degree,  although  it  is  believed  to  belong  with  and 
come  from  the  endogenous  metamorphic  granite  at  the  base  of  the 
series.  The  exotic  granite  has  sometimes  cut  rocks  as  new  as  the  Car- 
boniferous. Granite  grades  into  gneiss,  the  gneiss  into  mica  slate,  and 
the  mica  slate  into  argillite,  in  which  are  found  the  conglomerate 
bands.  In  these  conglomerates  in  many  cases  the  pebbles  have  been 
flattened,  bent,  and  even  drawn  out  into  lenticular  layers,  developing 
a  schistose  structure.    One  of  the  best  localities  is  that  at  Bellingham. 
The  Shawmut  group  is  a  fragmental  series  resting  unconformablv 
upon  the  Huronian  terranes.  The  chief  constituents  of  the  Shawmut 
group  are  breccia  and  amygdaloids,  the  relations  of  which  are  some- 
what uncertain.  The  petrosilex  breccia  of  the  Shawmut  group  are 
oftentimes  very  like  the  petrosilex  of  the  Huronian.  This  group  is 
perhaps  equivalent  to  the  copper-bearing  rocks  of  Lake  Superior, 
which  they  resemble  lithologically.  The  Paleozoic  formations  form 
troughs  wThich  rest  unconformablv  upon  the  older  series. 
Shaler,60  in  1889,  describes  Cape  Ann  as  consisting  mainly  of 
granite,  Avhich  is  cut  by  very  numerous  dikes  of  diabase  and  quite 
abundant  ones  of  quartz  porphyry.  Squam  River  is  an  area  of 
diorite.  The  relative  age  of  the  granite  and  diorite  has  not  been 
determined. 
Pumpelly,61  in  1889,  gives  a  systematic  general  account  of  the 
Green  Mountains  in  Massachusetts.  These  include  three  princi- 
pal elements — Hoosac  Mountain,  the  Taconic  Range,  and  the  great 
