HEW    ENGLAND.  571 
rock,  mica  slate.  At  North  Mountain,  separated  from  South  Moun- 
tain by  a  branch  of  Westville  River,  the  section  is  as  follows :  Horn- 
blende rock,  magnetic  iron  ore,  emery  7  feet,  hornblende  rock,  chlorite 
slate,  magnetic  iron  ore  6  feet,  talcose  slate,  magnetic  iron  ore  6  feet, 
mica  slate. 
Shaler,49  in  1871,  in  a  consideration  of  the  rocks  in  the  vicinity  of 
Boston,  states  that  there  can  be  no  doubt  that  the  syenites  of  eastern 
Massachusetts  are  the  oldest  rocks  found  in  the  region.  The  quarries 
at  Quincy  show  planes  of  separation  in  the  syenite  which  can  be  only 
referred  to  stratification,  despite  the  opinion  generally  entertained 
that  the  rocks  are  of  igneous  origin.  This  is  evidenced  by  the  fact 
that  in  the  deeper  portions  of  the  syenite  the  bedding  is  imperfect 
and  gradually  passes,  toward  the  exterior  of  the  rock,  into  a  more 
laminated  phase.  The  first  rocks  of  unquestionably  sedimentary 
origin  lie  north  of  Quincy  and  consist  of  bedded  sandstones  approach- 
ing quartzite.  This  series  is  fossiliferous.  The  alteration  of  the 
bedded  quartzite  at  Hayward  landing  is  so  great  that  the  rock  has 
assumed  something  of  the  appearance  of  a  gneiss.  In  addition  to 
these  rocks,  in  the  vicinity  of  Boston,  are  the  Roxbury  conglomerate 
and  the  Cambridge  slates.  In  the  latter  are  found  evidences  of 
organic  life  in  the  presence  of  numerous  indistinct  impressions  of 
fucoids.  It  is  believed  that  the  Cambridge  slates  and  the  Roxbury 
conglomerate  belong  to  the  same  great  series  of  beds.  As  there  is  a 
coincidence  in  the  direction  of  dip,  it  is  thought  that  they  all  may 
eventually  be  found  to  be  a  part  of  the  same  series  of  beds  as  the 
Braintree.  In  some  places  the  slates  have  a  perfect  cleavage  in  the 
plane  of  stratification.  Over  both  the  slates  and  the  conglomerates 
are  outflows  of  amygdaloid. 
Jackson,  50  in  1871,  states  that  there  is  an  insensible  passage  from 
the  syenite  into  the  greenstone  porphyry.  The  obscurely  stratified 
rocks  on  the  border  of  the  great  syenite  mass  at  Quincy  prove  the 
igneous  influence  of  the  eruptive  syenite  upon  the  upturned  strata 
which  it  had  elevated  by  its  protrusion. 
Dana,51  in  1872,  maintains  from  the  descriptions  of  full  sections 
that  at  Great  Barrington  is  a  conformable  succession  of  quartzite<. 
limestones,  mica  schists,  and  gneisses.  The  layers  of  quartzite  arc 
found  along  the  strike  to  change  to  mica  schist  and  gneiss.  This 
series,  many  of  them  later  in  age  than  the  Stockbridge  limestone,  is 
similar  to  the  Green  Mountain  series,  which  has  been  regarded  on 
lithological  evidence  as  pre-Silurian.  The  Stockbridge  limestone,  on 
fossiliferous  evidence,  is  found  to  be  either  Silurian  or  younger.  It 
appears  that  lithological  evidence  is  a  very  uncertain  tesl  as  to  geo- 
logical age,  for  crystalline  rocks  are  found  later  than  the  Stockbridge 
limestone,  quartzite  changes  into  mica  slate,  schist,  or  gneiss,  these 
into  hydromica  slates,  and  these  into  chloritic  mica  -late. 
