vanhtse.]  EASTERN    UNITED    STATES*  391 
the  limestones  are  changed  to  white  or  red,  coarse  grained,  crystalline 
limestone,  containing  various  crystallized  minerals,  with  scales  of 
plumbago,  and  rarely  show  any  traces  of  stratification.  The  slate  is 
changed  to  mica-slate,  micaceous  gneiss  or  hornblende-slate,  and  the 
quartz-rock  is  changed  so  as  to  be  scarcely  recognized  as  such.  In  the 
first  class,  also,  the  intrusive  rocks  bear  but  a  small  proportion  to  the 
altered  rocks  and  are  mostly  quartz  and  granite,  but  in  the  second 
class  the  undoubted  plutonic  rocks  abound  and  consist  of  granite, 
syenite,  greenstone,  augite,  serpentine,  diallage,  and  intrusive  metal- 
liferous veins. 
The  metamorphic  rocks  east  of  the  Hudson  and  Highlands  are  in  a 
continuous  range  from  Bennington  in  Vermont  to  the  w^est  part  of 
Massachusetts  and  Connecticut  and  the  eastern  part  of  New  York. 
Between  the  Taconic  rocks  and  the  metamorphic  rocks  to  the  east  no 
well  marked  line  of  distinction  can  be  drawn,  as  they  blend  into  each 
other  by  insensible  shades  of  difference.  In  considering  the  metamor- 
phic rocks  as  a  whole  the  descriptions  necessarily  include  certain  of  the 
Taconic  rocks.  The  strata  of  metamorphic  rocks  are  very  much  broken, 
so  that  no  stratum  has  been  traced  continuously  more  than  a  few  miles. 
The  only  beds  which  can  be  traced  with  any  degree  of  success  are  the 
limestones,  which  are  described  in  detail.  The  limestones  of  Westches- 
ter county  have  the  same  dip  and  line  of  bearing  as  the  contiguous 
gneiss,  and  like  that,  are  distinctly  stratified.  They  form  several  nearly 
parallel  ranges  at  intervals  of  2,  3,  or  4  miles.  They  all  dip  east-south- 
east, with  local  exceptions,  at  a  high  angle,  varying  from  45°  to  90°. 
The  metamorphic  slates  of  Dutchess,  Putnam,  Westchester,  and  New 
York  counties  have  been  traced  in  different  localities  through  different 
modifications  and  texture  from  the  gray  and  semicrystalline  limestones 
associated  with  talcose  slate  and  the  sandstone  of  the  Taconic  system, 
to  the  perfect  dolomites  and  white  and  gray  crystalline  marbles  asso- 
ciated with  mica- slate  and  granular  quartz-rock,  north  of  the  High- 
lands ;  and  to  still  more  crystalline  limestones  associated  with  mica- 
slate,  micaceous  gneiss,  hornblende- slate,  hornblendic  gneiss,  horn- 
blende-rock, syenite  and  granite,  south  of  the  Highlands.  In  these 
latter  limestones  are  frequently  found  some  mineral  substances,  such 
as  serpentine,  brown  tourmaline,  copper  and  iron  pyrites,  magnetic 
sulphuret  of  iron,  mica  and  magnesian  minerals,  particularly  where 
near  to  undoubted  plutonic  rocks.  It  is  believed  that  all  the  crystal- 
line limestones  of  Vermont,  Massachusetts  and  Connecticut  and  the 
eastern  part  of  New  York,  are  metamorphic  rocks;  *hat  they  were  origi- 
nally the  Mohawk  limestone  and  Calciferous  limestone,  and  that  the 
associated  rocks  were  originally  the  Potsdam  sandstone  and  the  slate 
rocks  of  the  Hudson  valley ;  that  they  were,  in  fact,  the  rocks  of  the 
Okamplain  division,  but  much  more  altered  and  modified  by  metamor- 
phic agency  than  the  Taconic  rocks. 
In  the  study  of  the  metamorphic  rocks  of  the  Highlands  and  Sara- 
