vax  bisk.]  EASTERN    UNITED    STATES.  371 
contact  tnetamorphism  has  a  zonal  character.  The  Banc  and  Orange 
bands  of  biotite-granite  so  combine- the  peculiarities  of  the  Cambrian 
conglomerate-gneisses  and  the  batholitic  gneisses  that  no  opinion  is 
expressed  as  to  their  origin. 
Pumpelly,65  in  1891,  describes  Cambrian  quartzite  as  resting  nn. 
conformably  upon  granitoid  gneiss  at  Clarksburg  mountain.  In  the 
granitoid  gneiss  is  found  a  dike  which  has  been  decayed  and  washed 
out  before  the  qnartzite  was  deposited,  leaving  a  fissure  which  caused 
the  beds  of  qnartzite  to  thicket)  and  sag,  and  which  contain  at  the  bot- 
tom material  derived  from  the  dike.  On  Hoosac  mountain  there  is 
a  core  of  granitoid  gneiss,  upon  which  rests  unconformably  at  the  axis 
coarse  basal  conglomerate  with  a  sharp  contact.  In  other  places  there 
is  an  apparent  gradation  between  the  metamorphosed  conglomerate 
and  the  granitoid  gneiss.  This  Cambrian  qnartzite- con  glomerate  is 
found  to  vary  laterally  in  the  legs  of  the  fold  into  comrdetely  crystal- 
line white  gneiss.  The  Cambrian  formation,  containing  Olenellus 
fauna,  mantles  around  the  pre-Cambrian  granitoid  gneiss,  and  the 
whole  mountain  is  an  overturned  fold. 
Pumpelly,66  in  1889,  gives  a  systematic  general  account-of  the  Green 
mountains  in  Massachusetts.  These  include  three  principal  elements, 
Hoosac  mountain,  the  Taconic  range,  and  the  great  valley  between 
these.  The  mountain  rocks  are  composed  of  crystalline  schists,  which 
are  found  to  be  of  Cambrian  and  Lower  Silurian  age,  resting  on  pre- 
Cambrian  rocks.  The  valley  has  a  floor  of  crystalline  limestone  or  sac- 
charoidal  marble,  on  which  are  ridges  of  schists,  both  being  of  Lower 
Silurian  age.  The  Taconic  range  is  a  synclinal  in  the  Lower  Silurian 
schists,  the  limestone  foundation  appearing  only  at  its  base.  At 
Hoosac  mountain  the  succession  is  (1)  granitoid  gneiss;  (2)  quartzite- 
con  glomerate  and  white  gneiss;  (3)  Hoosac  phyllite,  and  (4)  Rowe  schist. 
On  Greylock  the  succession  is  (1)  Stockbridge  limestone;  (2)  Berkshire 
phyllite;  (3)  Bellowspipe  limestone,  and  (4)  Greylock  phyllite.  At 
Hoosac  mountain  the  quartzite-conglomerate  and  white  gneiss  appear 
to  grade  down  into  the  granitoid  gneiss  in  perfect  conformity.  At 
Stamford  a  basic  dike  was  discovered  which  cuts  the  granitoid  gneiss, 
but  stops  abruptly  at  the  quartzite.  Indeed,  the  qnartzite  sags  down 
at  this  place,  its  layers  thickening  and  filling  the  hollow.  These  rela- 
tions are  considered  definite  proof  of  an  unconformity  between  the 
granitoid  gneiss  and  the  quartzite.  The  general  transition  between  the 
two  is  explained  by  considering  the  granitoid  gneiss  as  disintegrated 
at  the  time  of  the  transgression  which  formed  the  quartzite.  The 
quartzite-conglomerate  and  white  gneiss  are  traced  into  each  other  lat- 
erally, and  are  therefore  but  different  forms  of  a  sediment  of  the  same  age, 
and  unequally  metamorphosed.  Across  the  valley  the  Hoosac  phyllite 
was  traced  by  gradual  transitions  into  the  limestone;  and  the  Stock- 
bridge limestone,  Berkshire  phyllite,  Bellowspipe  limestone  and  Grey- 
lock phyllite  are  all  correlated  with  the  Hoosac  phyllite,     In  the  quartz- 
