364  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [buu.sg.; 
Hitchcock,  (C.  H.),40  in  1859,  describes  the  rocks  from  Greenfield  to 
Claremont,  Massachusetts,  as  having  the  following  order:  Micaceous 
slates  and  schists  interstratified  with  siliceous  limestone,  mica-slate 
hornblende-slate,  mica  slate  interstratified  with  limestone,  and,  lastly, 
calcareo-mica  slate,  The  dips  as  far  as  the  West  Sbelburne  falls  gneiss 
are  to  the  east;  at  this  latter  point  it  is  to  the  west.  The  whole  is  re 
garded  as  an  anticline. 
Gregory,41  in  1862,  describes  Marblehead  as  consisting  mainly  o 
the  Primitive  formation.  The  northern  part  of  the  peninsula  is  green 
stone,  intersected  by  dikes  of  the  same  rock.  In  the  southern  section 
syenite  contends  with  the  greenstone  for  supremacy,  for  here  the  twq 
rocks  are  thoroughly  in  term  i  n  gled.  The  deposits  of  greenstone,  sye  1 1  i  te, 
and  porphyry  are  for  the  most  part  distinct,  although  occasionally  the 
greenstone  grades  into  the  syenite, 
Jackson,42  in  1806,  gives  the  following  section  at  the  base  of  Sootlr 
mountain,  at  Chester,  Massachusetts,  from  the  base  upward:  Horn! 
blende  rock,  magnetic  iron  ore, emery  bed,  granular  quartzite,  chlorite-" 
slate  and  talc-slate,  crystallized  talc,  talcose  slate  rock,  soapstone  or 
talcose  rock,  mica-slate.  At  North  mountain,  separated  from  South 
mountain  by  a  branch  of  the  Westville  river,  the  section  is  as  follows: 
hornblende  rock,  magnetic  iron  ore,  emery  7  feet,  hornblende  rocM 
chlorite-slate,  magnetic  iron  ore  6  feet,  talcose  slate,  magnetic  iron  ore 
6  feet,  mica- slate, 
Shaler,43  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  quarriea 
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 I 
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  approaching  quartzite.     This  series 
is  fossiliferous.    The  alteration  of  the  bedded  quartzite  at  HaywarH 
landing  is  so  great  that  the  rock  has  assumed  something  of  the  appear- 
ance of  a  gneiss.     In  addition  to  these  rocks,  in  the  vicinity  of  Boston 
are  the  Koxbury  conglomerate  and  the  Cambridge  slates.     In  the  lat 
ter  are  found  evidences  of  organic  life   in  the  presence  of  numerous  in-  ^ 
distinct   impressions  of  fueoids.     It  is  believed   that  the   Cambridge 
slates  and  the  Koxbury  conglomerate  belong  to  the  same  gTeat  series 
of  beds.     As  there  is  a  coincidence  in  the  direction  of  dip  it  is  thought 
they  all  may  eventually  be  found  to  be  a  part  of  the  same  series  of  beds 
as  the  Braintree.     The  slates  have  a  perfect  cleavage  in  the  plane  of 
stratification  in  some  places.     Over  both  the  slates  and  conglomerates 
are  outflows  of  amygdaloid. 
Jackson,44  in  1871,  states  that  there  is  an  insensible  passage  from 
