NEW   ENGLAND.  573 
blende  rock,  diabase,  and  diorite,  usually  crypto-crystalline,  in  which 
no  indication  of  sedimentary  origin  can  be  traced.  The  syenites  con- 
sist of  quartz  and  feldspar,  with  little  or  no  hornblende.  The  por- 
phyry probably  belongs  with  the  crystalline  group,  and  pebbles  of  it 
are  abundant  in  the  Brighton  conglomerates.  Perhaps  some  of  the 
slates  are  so  altered  in  this  region  as  to  resemble  real  porphyry. 
In  the  second  division  arc  siliceous  slates  and  breccias.  The  sili- 
ceous slates  are  often  much  contorted.  At  Arlington  they  pass 
through  fine  grits  and  coarse  syenites  by  various  stages.  The  crystal- 
lines occupy  distinct  bands,  separated  by  more  recent  rocks  collected 
in  the  area  between  them.  These  more  recent  rocks  are  shown  to  be 
such  by  their  position  in  relation  to  the  underlying  crystallines,  as 
u ell  as  by  the  fact  that  they  are  composed  of  detritus  of  the  latter. 
In  places  they  are  fossiliferous,  and  at  Braintree  contain  the  Para- 
doxides  fauna.  These  stratified  rocks  are  in  part  slates  and  in  part 
conglomerates,  the  former  appearing  to  occupy  the  inferior  position. 
The  conglomerates  are  well  developed  in  the  vicinity  of  Newport  and 
Newberry.  Cutting  the  slates  and  conglomerates  are  rocks  which 
have  been  called  eruptives,  but  so  close  is  the  resemblance  in  chemical 
and  mineral  composition  and  in  appearance  to  the  more  fusible  por- 
tions of  the  crystallines  that  it  seems  almost  unreasonable  to  doubt 
that  the  former  were  derived  from  many  deep-lying  masses  of  the 
latter. 
Crosby,55  in  1876,  describes  and  maps  the  Eozoic  rocks  of  Massa- 
chusetts. They  are  divided  into  Norian,  Huronian,  and  Montalban 
on  lithological  and  chronological  grounds.  The  lithological  char- 
acters of  the  divisions  are  as  unlike  as  the  fauna  of  any  two  successive 
geological  formations.  The  Norian  is  found  in  two  areas  in  Massa- 
chusetts— that  including  the  city  of  Salem  and  adjacent  region  and 
that  which  includes  the  seaward  end  of  large  Nahant.  The  Norian 
rocks,  composed  chiefly  of  feldspar,  hornblende,  and  pyroxene,  are 
in  some  places  stratified  and  in  other  places  massive.  The  Huronian 
Vocks  occur  over  a  wide  area,  having  an  extreme  length  of  65  miles 
and  an  extreme  breadth  of  about  40  miles.  The  Huronian  comprises 
areas  marked  on  the  geological  map  of  Hitchcock  as  syenite,  por- 
phyry, and  hornblende  slate.  The  rocks  here  included  are  treated 
under  hornblendic  granite,  felsite,  diorite,  stratified  rocks,  and  lime- 
stones, all  of  which  are  regarded  as  metamorphosed  sedimentary 
beds.  The  Montalban  includes  granite,  which  comprises  exotic,  in- 
digenous, and  endogenous  forms,  gneiss,  mica  slate,  argillite,  and 
limestone.  Most  of  the  slates  in  the  vicinity  of  Boston  are  regarded 
as  of  Primordial  age,  although  fossils  have  been  found  only  at  Brain- 
tree.  The  argillite  of  Kents  Island  and  the  metamorphic  slate  of 
Newport  are  also  regarded  as  Paleozoic. 
