van  ra  EASTERN    UNITED    STATES.  373 
rocks  interstrat  ified  with  and  in  one  case  cutting  the  others,  amphibo- 
lites.  I>etailed  descriptions  are  given  of  ttie  occurrences  at  the  various 
districts. 
At  the  Hoosae  tunnel  the  main  facts  brought  out  are  that  there  is  a 
large  central  mass  of  coarse  granitoid  gneiss  (Stamford  gneiss)  forming 
the  core  of  Hoosae  mountain :  i  hat  tliis  is  flanked  on  both  sides  by  the 
white  gneiss-conglomerate  (Vermont  conglomerate),  the  eastern  band 
having  a  steady  dip  east  and  overlain  by  the  albite-schist  series;  tin- 
western  hand  broader,  with  varying  dips,  passing  by  gradual  transi- 
tions into  the  coarse  gneiss,  and  hounded  on  the  west  by  a  narrow  hand 
of  the  alhite  seliist  (Hoosae  schist),  the  contact  being  conformable  and 
transitional.  This  schist  is  succeeded  on  the  west  by  another  hand  of 
fine  grained  white  gneiss  (Vermont),  and  this  in  turn  by  the  limestone 
(Stockbridge),  no  contacts  being  observed.     The  structure  is  anticlinal. 
This  succession  and  these  relations  are  found  to  correspond  with  the 
distribution  in  the  central  district  of  Hoosae  mountain.  It  is  also  found 
that  the  anticlinal  of  Hoosae.  consisting  of  the  Stamford  gneiss,  Ver- 
mont formation  and  Hoosae  schist,  has  a  pitch  to  the  northward  of  from 
10°  to  15°,  while  the  western  side  has  been  overturned,  which  makes 
the  beds  in  inverted  order  on  tin-  west  side.  The  whole  northern  third 
of  the  region  and  a  broad  strip  along  the  east  is  occupied  with  albite- 
phyllite.  In  the  district  south  of  Cheshire  and  that  of  Hoosae  valley 
the  Stockbridge  limestone  and  Vermont  quartzite  are  found  to  be  con- 
formable, and  the  Latter  lower  in  horizon,  as  shown  by  contacts,  litho- 
logical  passages  and  the  corrugations  of  the  two  together;  the  quartzite- 
con  glomerate  of  the  Vermont  formation  is  identical  with  the  fine  grained 
white  gneisses  of  the  Dalton-  Windsor  area  and  to  those  of  Hoosae  moun- 
tain; and  the  schist  area  of  Hoosae  mountain  is  conformable  with  the 
quartzite  and  white  gneiss  series  of  Hoosae  valley.  The  Hoosae  valley 
schist  and  limestone  appear  to  be  conformable,  although  contacts  are 
wanting. 
At  Clarksburg  mountain  the  granitoid  gneiss  (Stamford  gneiss  is 
overlain  by  Clarksburg  quartzite  (Vermont  formation),  in  which  Wal- 
cott  has  found  remains  of  trilobites,  showing  it  to  be  Lower  Cambrian. 
The  two  in  a  general  way  appear  to  be  conformable,  but  in  one  place  an 
undoubted  dike  inns  in  a  straight  line  through  the  granitoid  gneiss. 
but  abuts  against  the  quartzite  without  passing  into  it :  and  thequartz- 
ite  has  a  curious  thickening  of  its  layers  where  the  dike  joins  it.  as 
though  there  had  been  a  hollow  owing  to  erosion  of  the  dike  before  the 
deposition  of  tin-  quartzite.  It  seems,  therefore,  to  show  the  most  per- 
fect unconformity  between  tin-  granitoid  gneiss  and  the  overlying  quartz- 
ite, although  the  structure  of  both  rocks  is  parallel.  Excepting  the 
granitoid  gneiss  and  the  amphibolite,  if  the  rocks  are  simply  the  Cam- 
brian and  Silurian  limestones,  sandstones  and  shales,  altered  by  meta 
morphism,  as  they  appear  to  be.  the  transition  ought  to  be  traced  to 
the  unaltered  forms  toward  the  Hudson.     An  examination  of  the  rocks 
