3(J0  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  Kix.80. 
cleavage  and  foliation  occur,  while  joints  are  found  both  in  the  stratified 
and  nnstratitied  rocks. 
Thompson,24  in  1801,  describes  the  greenstone  or  trap  dikes  of  parts 
of  Vermont.  These  are  found  to  cut  all  the  other  rocks  at  many  locali- 
ties. Besides  these  there  occur  calcareous  dikes,  veins  and  dikes  01 
quartz,  and  metallic  veins. 
Hitchcock,  (Charles  H.),25  in  1861,  gives  detailed  descriptions  of 
Sections  in  Vermont*  The  relations  of  the  Ascntney  syenite  to  the 
stratified  rocks  is  again  described.  Upon  examining  the  ledges  im- 
mediately contiguous  to  the  granite,  most  powerful  marks  of  altera- 
tion by  heat  are  found.  Everywhere  in  approaching  the  syenite  it  is 
surrounded  from  a  quarter  to  half  a  mile  with  indurated  schists  that 
ring  like  pot  metal  when  touched  with  a  hammer,  and  the  lime-rock 
that  is  usually  arranged  in  separate  strata,  seems  to  have  become  a 
constituent  part  of  each  stratum,  the  whole  rock  resembling  the  com- 
pact vitrified  quartz  west  of  the  Green  mountains.  Often  crystals  of 
staurotide,  and  perhaps  scapolite,  are  formed  in  the  schist  by  the  heat. 
In  the  west  part  of  the  larger  mountain  there  are  enormous  veins 
crawling  round  in  all  conceivable  directions  in  former  crevices  among 
the  schists.  This  syenite  is  full  of  nodules  of  hornblendic  masses, 
which  look  in  some  cases  much  like  pebbles.  They  are  probably  con- 
cretionary, and  are  all  allied  to  the  concretions  of  black  mica  in  granite 
at  Craftsbnry  and  elsewhere. 
Hall  (S.  R.),26  in  1861,  gives  many  details  as  to  the  geology  of  northern 
Vermont.  The  granites  are  here  particularly  abundant.  The  occur- 
rences are  such  as  to  lead  to  the  conclusion  that  they  are  eruptive  and 
that  in  their  eruptions  the  fragments  which  are  there  contained  have 
been  caught  from  the  strata  cut.  As  evidence  that  the  granite  has 
been  thrown  up  since  the  mica-schists  were  formed  are  cited  the  facts 
that  the  slates  on  the  borders  of  the  granite  furnish  unmistakable  signs 
of  contortion,  and  in  some  instances  of  change  both  in  the  direction  of 
the  strata  and  dip.  In  more  than  one  instance,  granite  is  found  over- 
lying the  calcareous  mica-slates,  and  in  one  instance,  at  Derby,  en- 
crinite  limestone  occurs  below  granite.  In  many  places  jointed  granite 
is  found  between  the  strata  of  slates,  conformable  to  them,  and  in  other 
instances,  in  dike  form,  crossing  the  strata  at  a  large  angle.  Frag- 
ments of  the  older  slates  are,  in  many  places,  found  imbedded  in  masses 
of  granite,  and  retain  the  characteristics  of  the  slates,  without  any 
essential  change.  Nodular  granite,  containing  masses  imbedded  like 
plums  in  a  pudding,  run  from  Memphremagog  lake  through  Derby, 
Brownington,  Irasburg,  Oraftsbury,  and  Calais. 
Hitchcock  (Charles  H.),27  in  1868,  gives  the  following  succession 
for  the  rocks  of  Vermont:  Ilnstratified  rocks,  including  granites,  sye- 
nite, protogine,  with  the  traps  and  porphyries;  Eozoic  system,  includ- 
ing Laurentian  gneiss  of  West  Haven  and  the  Green  mountain  gneiss; 
Paleozoic  system,  in  which  are  placed  the  Georgia  slates,  the  talcose 
conglomerate  and  schists,  the  mica-schists  and  other  formations. 
