van  hise.]  EASTERN    UNITED    STATES.  369 
Diller,54  in  1881,  describes  the  felsites  and  their  associated  rodks 
north  of  Boston.  The  granite  is  found  to  contain  fragments  of  dis- 
tinctly stratified  rocks,  and  is  regarded  as  an  eruptive  rock.  The  Id- 
sites  are  found  to  have  all  the  microscopical  characteristics  of  eruptive 
rocks;  to  cut  both  the  stratified  rocks  and  the  granites;  to  show  no 
transitions  into  tin1  clastic  rocks,  and  are  regarded  as  eruptives.  The 
diorites  contain  distinct  fragments  of  the  granites  and  felsites,  cut 
across  the  bedding  of  the  stratified  quartzites  and  schists,  and  are  erup- 
tives of  later  age  than  the  granite  and  felsite.  The  framgental  rocks 
are  in  part  older  and  in  part  younger  than  the  felsites,  as  a  portion  of 
them  is  cut  by  the  felsites  while  certain  conglomerates  contain  frag- 
ments derived  from  the  felsites. 
Wadsworth,55  in  1882,  states  that  the  Quincy  granite  is  eruptive, 
as  is  shown  by  the  fact  that  its  junction  with  the  slate  is  irregular. 
Along  the  contact  the  latter  rock  is  greatly  indurated  and  changed  in 
color,  and  the  granite  has  lost  its  distinctive  characters,  being  trans- 
formed into  a  spherulitie  quartz-porphyry. 
Wadsworth,56  in  1882,  describes  as  a  trachyte  at  Marblehead  neck 
and  having  all  the  characteristics  of  this  eruptive  rock,  a  rock  which 
Crosby  has  described  as  a  sandstone  or  arenaceous  slate. 
Wadsworth,57  in  1884,  describes  the  relations  of  the  argillite  and 
conglomerate  of  the  Boston  basin.  At  the  junction  of  the  two  the 
argillite  is  found  to  be  irregularly  eroded  and  the  conglomerate  laid 
down  unconformably  over  it;  in  places  the  argillite  is  cut  off  and  the 
conglomerate  abuts  unconformably  against  it,  and  pebbles  of  the  argil- 
lite are  found  in  the  conglomerate  at  the  junction.  There  are  at  least 
two  distinct  argillites.  One,  underlying  the  conglomerate  at  Beacon 
street,  resembles  that  of  the  Paradoxides  argillite  at  Braintree;  the 
other,  of  a  coarser  grain,  oftentimes  a  true  sandstone  as  far  as  its  rela- 
tions have  been  ascertained,  is  a  component  part  of  the  Roxbury  con- 
glomerate. So  far  as  any  evidence  is  at  hand,  the  oldest  surface  rocks 
in  the  basin  are  the  argillites  and  schists.  Of  these  the  age  of  only  a 
small  area  at  Braintree  carrying  Paradoxides  is  known.  Through  the 
schists  and  argillites  have  been  protruded  immense  quantities  of  erup- 
tive rocks  in  the  forms  of  lava  Hoavs,  ashes,  dikes,  and  bosses. 
Perry,58  in  1885,  states  that  the  mica-schist  at  Worcester  contains  a 
jpal  seam,  and  bears  fossils  of  Carboniferous  age.  The  mica-schist  is 
;ut  by  granite. 
Jtjlien,51*  in  18S7,  describes  the  succession  of  rocks  in  the  Great  Bar- 
ington,  from  the  base  upward,  as  consisting  of  Stockbridge  limestone, 
schist  or  gneiss,  quartzite,  and  dolomite.  The  proof  that  tin1  dolomite 
>ccupies  a  distinct  bed  at  a  higher  horizon  from  the  main  sheet  is  clear. 
Emerson,60  in  1887,  describes  the  succession  of  crystalline  rocks  in 
[lampsh ire  county,  in  order  of  their  age  from  the  base  up,  as  gneiss, 
eldspathic  mica-schist,  hornblende-schist,  hydromica  schist,  and  calcil- 
Bull.  80 24 
