604  pre-cambria:n  geology  of  north  America. 
The  dikes  are  found  to  be  bostonites,  diabases,  camptonites,  fourchite, 
and  monchiquite. 
Cushing,20  in  1894,  mentions  pre-Cambrian  rocks  in  Saranac 
Township  and  Beekmantown,  N.  Y.  These  comprise  gneisses  and 
gabbro,  upon  which  the  Cambrian  rests  unconformably. 
Smyth  (C.  H.),27  in  1894,  describes  a  group  of  diabase  dikes  as 
breaking  through  the  granite,  gneiss,  and  quartzite  in  the  vicinity  of 
the  village  of  Gannanoque,  Ontario,  the  whole  being  overlain  by 
Potsdam  sandstone. 
White,28  in  1894,  describes  and  maps  the  geology  of  Essex  and 
Willsboro  Townships,  Essex  County,  N.  Y.  The  Archean  rocks  of 
the  townships  comprise  the  following:  (1)  Labradorite  rocks,  gab- 
bros,  norites,  and  anorthosites,  occupying  the  western  half  of  the  area, 
west  of  Boquet  River;  (2)  the  metamorphic  crystalline  limestones 
and  ophicalcites  in  the  northeastern  part  of  the  area  on  Willsboro 
Bay,  and  in  the  southeastern  part  of  the  area  on  the  ridge  of  Split 
Rock  Point;  (3)  gneisses  and  granites,  chiefly  on  Split  Rock  Point. 
Following  Adams,a  White  classes  all  these  rocks  as  Norian  or  Upper 
Laurentian. 
Kemp,29  in  1894,  describes  the  gabbros  of  the  western  shore  of  Lake 
Champlain.  The  rocks  occurring  in  this  area  comprise  (1)  gneisses, 
(2)  crystalline  limestones,  including  black  hornblendic  and  pyroxenic 
schists  and  gneisses,  and  (3)  anorthosites,  including  gabbro  proper, 
olivine  gabbros,  and  norites.  The  anorthosites  over  large  areas  have 
been  profoundly  affected  by  dynamic  action,  and  in  many  places 
now  have  a  gneissic  structure.  In  the  anorthosites  at  various  places, 
and  particularly  at  Split  Rock  Mountains,  forming  the  more  basic 
crystallization  from  the  original  magma,  are  lean,  titaniferous  mag- 
netites which  have  been  mined  as  iron  ores.  At  the  contacts  of  the 
gabbro  and  limestone  the  latter  rock  has  been  bent  by  dynamic  move- 
ments; various  silicates  have  developed  within  it,  among  which  are 
scapolite,  hornblende,  pyroxene,  and  titanite.  The  limestone  is  also 
coarsely  crystalline.  Since  the  intrusion  of  the  gabbro  the  limestone 
has  been  subjected  to  dynamic  movements,  and  exhibits  strongly 
the  characteristic  plasticity  of  this  rock  under  stress. 
Smyth  (C.  H.),30  in  1894,  gives  a  petrographical  description  of  the 
gabbros  of  the  southwestern  Adirondack  region,  and  of  black  horn- 
blende gneiss  which  occurs  in  the  same  area.  The  most  altered  form 
of  the  gabbro  is  very  similar  to  the  hornblende  gneiss,  and  it  is  sug- 
gested that  the  latter  is  but  an  extremely  metamorphosed  phase  of 
the  former. 
Kemp,31  in  1894,  describes  the  geology  of  Essex  County,  N.  Y.  The 
pre-Cambrian  succession  in  this  county  is  as  follows:   (1)  A  gneissic 
a  Adams,  F.  D.,  Ueber  das  Norian  oder  Ober-Laurentian  von  Canada  :  Neues  .Tahrb.,  Beil. 
Band  8,  p.  423. 
