578  PRE-CAMBRIAN    GEOLOGY   OF    NORTH   AMERICA. 
Emerson,64  in  1890,  describes  the  rocks  of  central  Massachusetts, 
between  the  Berkshire  limestone  and  the  Boston  basin,  as  consisting 
of  a  series  of  mica  schists,  quartz  schists,  and  hornblende  schists,  pre- 
sumably Paleozoic,  and  eight  bands  of  granite  and  granitoid  gneiss, 
in  small  part  Archean,  in  larger  part  Cambrian,  and  in  largest  part 
intrusive.  In  the  western  part  is  a  small  row  of  Archean  ovals, 
about  which  are  the  Cambrian  conglomerates  and  conglomerate 
gneisses,  the  latter  rocks  having  a  quaquaversal  arrangement.  Here 
are  included  the  Princeton  and  Athol  granites,  often  well  foliated, 
which  have  a  great  extent  north  and  south.  To  the  great  intrusive 
masses  of  granite  is  applied  Suess's  name  batholiths.  These  have 
melted  their  way  through  a  great  thickness  of  folded  strata  and 
absorbed  much  of  the  latter  in  their  own  mass.  At  times  the  central 
masses  of  granite  are  cut  by  dikes  of  coarse  muscovite  granite,  which 
seem  to  be  later  intrusions.  About  the  batholiths  are  broad  areas  in 
which  contact  metamorphism  has  altered  the  rocks,  changing  the 
argillites  to  mica  schists,  etc.  The  contact  metamorphism  has  a  zonal 
character.  The  Barre  and  Orange  bands  of  biotite  granite  so  com- 
bine the  peculiarities  of  the  Cambrian  conglomerate  gneisses  and  the 
batholithic  gneisses  that  no  opinion  is  expressed  as  to  their  origin. 
Pumpelly,65  in  1891,  describes  Cambrian  quartzite  as  resting  un- 
conformably  upon  granitoid  gneiss  at  Clarksburg  Mountain.  In  the 
granitoid  gneiss  is  found  a  dike  which  has  been  decayed  and  washed 
out  before  the  quartzite  was  deposited,  leaving  a  fissure,  which 
caused  the  beds  of  quartzite  to  thicken  and  sag  and  which  contains 
at  the  bottom  material  derived  from  the  dike.  On  Hoosac  Mountain 
there  is  a  core  of  granitoid  gneiss,  upon  which  rests  unconformably 
at  the  axis  coarse  basal  conglomerate  with  a  sharp  contact.  In  other 
places  there  is  an  apparent  gradation  between  the  metamorphosed 
conglomerate  and  the  granitoid  gneiss.  This  Cambrian  quartzite 
conglomerate  is  found  to  vary  laterally,  in  the  legs  of  the  fold,  into 
completely  crystalline  white  gneiss.  The  Cambrian  formation,  con- 
taining Olenellus  fauna,  mantles  around  the  pre-Cambrian  granitoid 
gneiss,  and  the  whole  mountain  is  an  overturned  fold. 
Sears,66  in  1894,  gives  a  description  of  each  of  the  rocks  of  Essex 
County,  Mass.  These  comprise  plutonic  rocks,  volcanic  rocks,  Archean 
rocks,  and  various  metamorphosed  sedimentary  rocks  of  Paleozoic 
age. 
Emerson,67  in  1894,  gives  an  outline  of  the  geology  of  the  Green 
Mountain  region  in  Massachusetts.  The  Algonkian  rocks  comprise 
the  Washington  gneiss,  Tyringham  gneiss,  East  Lee  gneiss,  Hinsdale 
limestone,  and  Hinsdale  gneiss.  This  series  is  the  equivalent  of  the 
Stamford  gneiss  in  Hoosac  Mountain.  The  Algonkian  rocks  consist 
of  firm,  coarse  gneisses  which  contain  minerals  and  possess  structures 
not  formed  in  the  later  rocks ;  thick  beds  of  coarse  and  highly  crystal- 
line limestones  which  contain  many  minerals  rarely  found  in  later 
